ANNUAL REPORTSON THEPROGRESS OF CHEMISTRYGENERAL AND PHYSICAL CHEMISTRY.RADIO-FREQUENCY SPECTROSCOPY.ABOUT five hundred papers of chemical interest have appeared on this topicsince the last Report 1 on it in 1955. Nuclear magnetic resonance (NMR,NSR) is the most active field, closely followed by electron (paramagnetic)resonance (EPR, EMR, or ESR). Both methods are being applied to almostany system which will give spectra. They can deal with a wide variety ofmaterials, and are often powerful in revealing special phenomena related tostructure. Microwave spectroscopy of gases remains unrivalled for its powerto yield structural detail about simple polar molecules, and continues to beso applied to diverse suitable substances. Nuclear quadrupole resonance(NQR) has developed more slowly, but is being used to study the interactionsof an increasing variety of quadrupole nuclei with their environments.Microwave Spectroscopy.-Development of technique has continued onestablished lines.Gordy and his collaborators have extended the high-frequency limit of the radio-frequency range to over 500,000 Mc./sec., awavelength of under 0.6 min., and have measured spectra there. They alsodescribe a high-temperature molecular beam spectrometer in which ro-tational transitions are measured for K+Cl- and Na+Cl- at 3 mm. wave-lengths. A spectrometer of exceptional sensitivity (minimum absorptioncoefficient 5 x cm.-l) has been described4 for wavelengths near 3 cm.Very accurate measurements of dipole moments have been made in aninstrument in which a Stark-effect field of great precision is applied. Designshave been given for non-metallic absorption cells suitable for work withfree radicals.The rotation spectrum of HI has been measured,2 the first such work ona diatomic hydride containing the ordinary hydrogen isotope.of the rotation spectrum of ND, is notable, since the immense amount ofThe studyJ .13. Callomon, D. M. Simpson, and N. Sheppard, Awn. Reports, 1955, 52, 81.M. Cowan and W. Gordy, Phys. Rev., 1956,104, 551.A. K. Garrison and W. Gordy, ibid., 1957, 108, 899.H. G. Fitzky, R. Honerjager, and W. Wilke, 2. Physik, 1957, 149, 471.S. A. Marshall and J. Weber, Phys. Rev., 1957, 105, 1502; Rev. Sci. Instr., 1957,E. B. Brackett, P. H. Kasai, and R.J . Myers, ibid., p. 699; C. C. Costain, Canad.G. Erlandsson and W. Gordy, Phys., Rev., 1957, 106, 513.28, 134.J . Phys., 1957, 35, 2418 GENERAL AND PHYSICAL CHEMISTRY.microwave work on NH, has been confined to its inversion spectrum. Thespectrum of ND, shows interesting inversion-doubling.Several asymmetric-top structures have been fully determined.Hydrogen selenide * has d(Se-H) = 1.460 j= 0.013 k and L HSeH =91.0" -J= 0.6"; the dipole moment is 0.24 & 0.02 D. Nitrogen dioxide hasd ( N - 0 ) = 1-197 A and LON0 = 134" 15'. Bromine trifluoridelo has theplanar distorted-T configuration, with d(F-Br) = 1.810 A twice sym-metrically, the unique d(F'Br) = 1.721 A and LFBrF' = 86' 13'. Sul-phuryl fluoride l1 has d(S-0) = 1.405 & 0.003 k, d(S-F) = 1.530 -+ 0.003 k,LOSO = 123" 58' & 12', and LFSF = 96" 7' & 10'; the dipole moment is1.110 & 0-015 n.In SiH,F, the Si-F length l2 of 1.577 0.001 k is inter-mediate between the lengths found in SiH,F and SiF,H; other parametersare d(Si-H) = 1.47 5 0.01 A, LFSiF = 107" 56' &- 6', and LHSiH =112" 1' & 30'; the dipole moment is 1-54 & 0.02 D. A notably thoroughstudy of formamide l3 yields a planar structure with d(C-0) = 1.243 3118" 59' & 30', LNCO = 123" 35' 5 21', and LNCH == 103" 54' & 1.2";the dipole moment of 3.714 -+ 0.06 D makes an angle of 39.6" with the C-Nbond; the quadrupole coupling constants for 14N are 1.9 Mc./sec., 1.7 Mc./sec.,and -3.6 Mc./sec. with reference to the A , B, and C axes respectively.Another outstanding case is that of thiophen l4 for which enough spectrahave now been measured for all eight structural parameters to be determined.For a variety of other molecules, including several cyclic compounds, fewerdata have been published, but significant advances have been made towardsfull structure determinations.Molecules with restricted internal rotation continue to be the subject ofvery important contributions , particularly from Wilson and his school.Barrier heights for many such cases are determinable from the splittingsdue to the tunnelling of hydrogen atoms through the barrier.In a summaryof many of the data,l5 Wilson concludes that the barrier heights are decidedto a considerable extent by the electronic structure of the bond about whichtorsion occurs.Some studies have been combined with particularly elegantstructure determinations, including the establishment of the relative equi-librium positions of the rotating groups. Thus for acetaldehyde l 6 d(C-H)-(methyl) = 1-09 A, d(C-H)(aldehyde) = 1-11 A, LHCH = 108.3", d(C-C) =1-501 A, d(C-0) = 1.216 k, LCCH = 117-5", and LCCO = 124"; a tequilibrium configuration the aldehyde oxygen eclipses one of the methylhydrogen atoms; the barrier height is 1150 & 50 cal./mole and the dipolemoment 2.69 D at an angle of 18" 52' with the A-axis. Methylsilane l7 has0.007 A, d(C-N) = 1.343 & 0.007 A, d(N-H) = 0.995 & 0.007 A, LHNH =8 A. W. Jache, P. W. Moser, and W. Gordy, J . Chem. Phys., 1956, 25, 209.G.R. Bird, ibid., p. 1040.l o D. W. Magnuson, ibid., 1957, 27, 223.l1 D. R. Lide, D. E. Mann, and R. M. Fristrom, ibid., 1957, 28, 734.l2 V. W. Laurie, ibid., p. 1359.l3 R. J. Kurland and E. B. Wilson, jun., ibid., 1957, 27, 585.l4 13. Bak, D. Christensen, J. Rastrup-Andersen, and E. Tannenbaum, ibid., 1956,1 5 E. B. Wilson, jun., Proc. Nat. Acad. Sci. U.S.A., 1957, 43. 816.l6 R. W. Kilb, C . C. Lin, and E. B. Wilson, jun., J . Chem. Plzys., 1957, 26, 1695.1 7 R. W. Kilb and L. Pierce, ibid., 1957, 27, 108.25, 892SHERIDAN : RADIO-FREQUENCY SPECTROSCOPY. 9the expected staggered configuration, with a barrier height of 1700 & 100cal./mole; among the full set of determined parameters is a particularlyprecise length for the Si-C bond length, 1.8668 & 0.0005 A.Methylamine l8has a barrier height of 1980 cal./mole; the dipole moment of 1.326 & 0.015 Dmakes an angle of 76" 40' with the A-axis; the quadrupole couplingconstants for 14N are 2.35 Mc./sec., 2.12 Mc./sec., and -4.47 Mc./sec. withreference to the A , B, and C axes respectively.The theory of the internal rotation problem has been developed con-siderably,l6> l99 2O and in particular tables of Mathieu integrals and othernumerical quantities involved in the computations have been madeavailable.21Several studies concern primarily the effects of quadrupole coupling.Thus the coupling constant for the deuteron 22 along the O-D bond in D,Ois 353 & 4 kc./sec., and the coupling of l70 in HD170 has been used 23 toevaluate the quadrupole moment of that oxygen isotope. From thisknowledge of the nuclear moment and the quadrupole coupling constant of1 7 0 in C170, it is found that the electronic structure of carbon monoxidemust differ in an important way from the conventional concept of thebonding.Electron Resonance.-Electron resonance due to simple ions in crystals,and effects essentially related to crystal structure and nuclear properties,have recently been reviewed.25 McConnell 26 has reviewed the more chemicalaspects of electron-spin resonance (and nuclear magnetic resonance) up toDecember, 1956.A commercial electron-spin resonance spectrometer is now offered 27which uses 3 cm.radiation and has high sensitivity, sufficient to detectabout Details havebeen given 28 of an instrument employing 1.25 cm. radiation which is aboutas sensitive at room temperature with wide-band detection, but which shoulddetect much less than 10-l1 mole of electron spins at low temperatures withnarrowed band-width.A further instrument has also been fully described.29Some of the simplest stable paramagnetic substances to be studied arechlorine dioxide and the alkali super oxide^.^^ In each case the unpairedelectron is shown to be associated with the bonding orbitals, as previouslybelieved.mole of electron spins with a narrow resonance.l 8 D. R. Lide, J . Chem. Pliys., 1957, 26, 343; D. Kivelson and D. R. Lide, ibid.,2o J. D. Swalen, ibid., 1956, 24, 1072.21 D. R. Herschbach, ibid., 1957, 27, 975.22 D.W. Posener, Austral. J . Phys., 1957, 10, 276.23 M. J. Stevenson and C. H. Townes, Phys. Rev., 1957, lG7, 635.24 B. Rosenblum and A. H. Nethercot, J . Chem. Phys.. 1957, 27, 828.25 K. D. Bowers and J. Owen, Re$. Progr. Plays., 1955, 18, 304; D. M. S. Bagguley26 H. M. McConnell, Ann. Rev. Phys. Chem., 1957, 8, 105.27 Varian Associates, Palo Alto, California.2 8 A. A. Buckmaster and H. E. D. Scovil, Canad. J . Phys., 1966, 34, 711.29 M. W. P. Strandberg, M. Tinkham, I. H. Solt, jun., and C. F. David, jun., Rev.50 J . E. Bennett, D. J . E. Ingram, and D. Schonland, Proc. Phys. Scc., 1956, 69,p. 353; T. Nishikawa, J . Phys. SOC. Japan, 1957, 12, 668.K. T. Hecht and D. M. Dennison, J . Chem. Phys., 1957, 26, 31, 48.and J. Owen, ibid., 1957, 20, 304.Sci.Instv., 1956, 27, 596.A , 55610 GENERAL AND PHYSICAL CHEMISTRY.Many electron-spin resonance studies concern bonding in transition-metalcomplexes. The anisotropic g-factor in copper acetylacetone 31 does notagree with the simple Pauling treatment of the bonds, but is more compatiblewith a molecular-orbital approach. For Cu(NH,),SO4,H2O two independentstudies 32 have been differently interpreted regarding the covalent characterof the Cu-N bonds. Some of the most interesting work deals with extensiveapproximately planar arrangements about a paramagnetic atom. In acidmethzemoglobin 33 the g-factor is strikingly anisotropic, being 2-00 & 0.01 inthe haem plane and 6.00 & 0.05 in an axis perpendicular to it. Informationon the bonding of the iron atom and on the crystal structure are bothobtainable.Different results with haemoglobin azide and hydroxide 34 arein accord with the greater degree of covalency ascribed to the iron in suchmaterials. In the azide the g-factor perpendicular to the hzm plane is 2.80,and that in the plane varies from 1.72 to 2.22; a theoretical treatment ofthe bonding has been given.35 Resonance in copper porphin derivatives hasalso been studied,36 and the splitting which appears when chlorine is attachedto the edge of the planar sheet is taken to indicate that the unpaired electronorbital extends across some 9 A similar long-rangeeffect is found in the dibenzenechromium cation,37 where fine structure dueto the coupling of the electron spin with all twelve protons is observed.Relatively stable free radicals of known structure are much studied ;electron-spin resonance of radicals has been reviewed.38 Several papersconcern radicals containing nitrogen, such as derivatives of (C,H,),N anddiphenylpicrylhydrazyl.Line-widths for a series of such radicals have beencorrelated 39 with Hammett’s sigma functions of substituents and discussedin terms of delocalization of electrons. Proton fine structures have beenmeasured in diradicals such as those in which two triphenylmethyl structuresare joined, through their benzene rings, by a saturated chain; 40 spin-exchange in such cases has been studied 41 by the introduction of carbon-13.Semiquinone structures, for example the 1 : 4-naphthasemiquinonecontinue to receive at tention, and molecular-orbital theory has been ap-plied43 to account for the proton fine structures observed.The seventeenelectron-spin resonance peaks of the naphthalene negative ion have alsobeen interpretedu in terms of the spin-densities at the protons; the extrato the chlorine nuclei.31 B. R. McGarvey, J . Phys. Chem., 1956, 60, 71.32 E. H. Carlson and R. D. Spence, J . Chem. Phys., 1956, 24, 471; H. Abe ands3 J. E. Bennett, J. F. Gibson, and D. J. E. Ingram, Proc. Roy. Soc., 1957, A , 240,34 J . F. Gibson and D. J. E. Ingram, Nature, 1957, 180, 29.35 J. S. Griffith, ibid., p. 30.36 D. J. E. Ingram, J . E. Bennett, P. George, and J . M. Goldstein, J . Amer. Chem.37 R. D. Feltham, P. Sogo, and M. Calvin, J .Chem. Phys., 1957, 26, 1354.S. I. Weissman, T. R. Tuttle, jun., and E. de Boer, J . Phys. Chem., 1957, 61, 28.39 R. I. Walter, R. S. Codrington, A. F. d’-4damo, jun., and H. C. Torrey, J . Chem.40 H. S. Jarrett, G. J. Sloan, and W. R. Vaughan, ibid., p. 697.41 D. C. Reitz and S. I. Weissman, ibid., 1957, 27, 968.4 2 J . E. Wertz and J. L. Vivo, ibid., 1956, 24, 479.4s R. Bersohn, ibid., p. 1066; H. M. McConnell, ibid., p. 632.44 T. R. Tuttle, R. L. Ward, and S. I. Weissman, ibid., 1956, 25, 189.K. Ono, J . Phys. SOC. Japan, 1956, 11, 947.67; J. S. Griffith, ibid., 1956, A , 235, 23.SOC., 1956, 78, 3545.Phys., 1956, 25, 319SEERIDAN : RADIO-FREQUENCY SPECTROSCOPY. 11splitting when carbon-13 is at the a-position is discussed45 in terms of theoccurrence of the unpaired electron in both o and x orbitals.Less completetreatments of the negative ions of anthracene and diphenyl 46 accord withthese ideas. A highly symmetrical radical, formed on removal of a hydrogenatom from perinaphthene,*’ is identified from proton splitting in its electronresonance spectrum. The theory of hyperfine interactions in aromatic radicalshas been developed,48 particularly in terms of spin-densities, and it has beenemphasised49 that these densities can be negative, the polarisation at apoint sometimes being opposite to the total spin polarisation of the molecule.The resonance of the naphthalene negative ion is broadened 50 by theaddition of naphthalene, owing to electron exchange between C1,H8- andCl0H8.From this effect rate constants have been evaluated for the exchangeprocess in the presence of various cations and solvents.Liquid sulphur is a complex dynamic system of free radicals, with para-magnetism increasing reversibly as the temperature is raised.51 A thoroughstudy by electron-spin resonance confirms the existing statistical theory ofthe radicals present. Other one-element systems rich in free radicals arethe carbons, on which work has continued 52 in efforts to understand morefully these complex structures.Much research concerns unstable or unidentified radicals, since electron-spin resonance is powerful in detecting traces of paramagnetic species. Insome, but by no means all, such cases, evidence of identity of the species isobtainable.Wide use is made of proton fine-structure for identification.Thus X-irradiation 53 of solid dimethylmercury yields probably C2H,+, andof diethylmercury, C2H, ; dimethylzinc appears to give CH,. and ZnCH,+.Methanol and acetamide, so irradiated,5* probably produce CH2+ and,analogously, C2H,+ is reported from ethanol and from propionamide.Radicals formed by oxidation of diarylamines 55 show nuclear fine structuresin their electron-spin resonance spectra, and are probably important inconnexion with their antioxidant and polymerization-inhibiting properties.Several aromatic substances yield free radicals when dissolved in con-centrated sulphuric acid, When aryl sulphides are so dissolved, the radicalshave been assigned structures 56 from proton splittings.The radicals soformed from fused-ring hydrocarbons have electron-spin resonance spectra 57resembling those of the corresponding negative ions, and it is thought thatthe solutions contain analogous positive ions.Attempts have been made to study simple free radicals, normally formed45 T. R. Tuttle and S. I. Weissman, J . Chem. Plzys., 1956, 25, 189.46 E. de Boer, ibid., p. 190.4 7 P. B. Sogo, M. Nakazaki, and M. Calvin, ibid.. 1957, 26, 1343.4 8 H. M. RlcConnell, ibid., 1956, 24, 764; S. I. Weissman, ibid., 1956, 25, 890.4 9 H. M. McConnell and D. B. Chesnut, ibid., 1957, 27, 984.50 R. L. Ward and S. I. Weissman, J . Amer. Chem SOC., 1957, 79, 2086.D. M. Gardner and G. K. Fraenkel, ibid., 1956, 78, 3279.52 D. E. G. Austen and D.J. E. Ingram, Chem. afzd Ind., 1956, 981; N. S.53 W. Gordy and C. G. McCormick, J . Amer. Chem. SOC., 1956, 78, 3243.54 C. F. Luck and W. Gordy, ibid., p. 3240.5 5 R. Hoskins, J . Chem. Phys., 1956, 25, 788.56 A. Fava, P. B. Sogo, and M. Calvin, J . Amer. Chem. SOC., 1957, 79, 1078.57 S. I. Weissman, E. de Boer, and J. J. Conradi, J . Chem. Phys., 1957, 26, 963.Garif’yanov and B. M. Kozyrev, Zhur. eksp. teor. F i z . (U.S. translation), 1956, 3, 25512 GENERAL AND PHYSICAL CHEMISTRY.transiently under conditions such as those in a.n electric discharge, bytrapping them at low temperatures. The afterglow of active nitrogen, whenso condensed at 4" K, was shown 58 to contain free nitrogen atoms. Trappedradicals, thought to be H02 or possibly OH, have been detected by electron-spin resonance in products from a discharge.59 Though identification maynot be easy, there will clearly be much further work of this type.Nuclear Magnetic Resonance.-Papers on technique include details of ahigh-resolution spectrometer,co and treatments of magnet design 61 andstabilization.62 Especially notable is a spectrometer of high stability,a inwhich the master oscillator is locked to the resonant frequency of a controlsample in the magnetic field, the Larmor condition thus being preserved.The immense resolution now attainable is shown by the most refined workon ethanol,64 for which 26 lines are now resolved, some only 0.5 c./sec.apartat 30 Mc.jsec. Modulation at a frequency high compared with the spectralsplittings is suggested 65 for highly sensitive detection without loss of detail.Standardization of spectra is fully discussed,66 and small spin-spin couplingconstants can be measuredG7 by use of the "ringing patterns " on thespectral trace.Methods are given for heating the sample to temperaturesup to 300" c , ~ ~ and for cooling it to low temperature^.^^ Work at lowmagnetic fields is active, and a low-field spectrometer, chiefly suited tomeasurements of relaxation times, has been described.70 The method offree precession in Earth's field, in which nuclei of slightly different precessionfrequencies are revealed by beats in the decaying signa1,'l should be a usefuladjunct to normal methods. Spin-echo technique can be quite simplyapplied in Earth's field, with no special preca~tions,~2 for work on relaxationphenomena.Reviews of chemical aspects of nuclear magnetic resonance up to the endof 1956 are available.261 73Work continues on solids to determine internuclear distances, such as theinter-proton distance in the a i d e ion,7* and to study molecular motions.A number of papers deal with molecular mobility and crystallinity inpolymers, such as rubber.75 Line-widths have given information about58 T.Cole, J. T. Harding, J. R. Pellam, and D. M. Yost, J . Chem. Phys., 1957, 27, 593.R. Livingston, J. Ghormley, and H. Zeldes, ibid., 1956, 24, 483.6 0 €3. Primas and H. H. Gunthard, Helv. Phys. Acta, 1957, 30, 315; H. Primas,61 Idem, ibid., p. 331.6f Idem, Rev. Sci. Instr., 1957, 28, 510.63 E.B. Baker and L. W. Burd, ibid., p. 313.64 J. T. Arnold, Phys. Rev., 1956, 102. 136.6 5 K. Halbach, Helv. Phys. Acta, 1956, 29, 37; R. V. Pound, Rev. Sci. Instr., 1957,6 6 J. R. Zimmerman and M. R. Foster, J . Phys. Chem., 1957, 61, 282.67 C. A. Reilly, J . Chew. Phys., 1956, 25, 604.6 8 J. N. Shoolery and J. D. Roberts, Rev. Sci. Insbr., 1957, 28, 61.69 N. Fuschillo, ibid., 1956, 2'7, 394; L. N. Mulay, ibid., 1957, 28, 279.70 P. W. Mitchell and M. Eisner, ibid., p. 624.7 1 D. F. Elliott and R. T. Schumacher. J . Chem. Phys., 1957, 26, 1360.72 J. G. Powles and D. Cutler, Natuve, 1957, 180, 1345.73 J. E. Wertz, J . Phys. Chem., 1957, 61, 51.74 R. Freeman and R. E. Richards, TTans. Faraday SOC., 1956, 52, 802.7 5 H. S. Gutowsky, A.Saika, M. Takeda, and D. E. Woessner, J . Chem PAys., 1957,ibid., p. 297.28, 966.27, 534SHERIDAN : RADIO-FREQUENCY SPECTROSCOPY. 13rotational isomerism ; for instance, fluorine magnetic resonance in solidCFCl,*CFCl, indicates the gauche f0r11-p and configurations are assigned toCHCl,*CHCl, and CHBr,*CHBr, from proton resonance. 7 7 High resolutionis applied to similar problems, since spectra of liquids are also sensitive toconfigurational effects ; cases include gem-difluoroethanes, 78 where evidenceof restricted rotation is obtained and the temperature dependence of theresidence-times in various configurations can be studied, 79 dimethyl-formamide and dimethylacetamide,80 which have planar equilibriumskeletons, alkyl nitrites,81 of which cis and trans forms are detectable,and nitrosamines Ba where there is hindered rotation about the N-Nbond.Very large and structurally important field shifts occur 83 for fluorineresonances in crystals containing paramagnetic ions, notably in manganousfluoride, MnF,.Similar paramagnetic shifts even occur when the nucleusin resonance is separated from the paramagnetic ion by another atom,s4 forexample in the phosphorus resonance in lithium manganous phosphate,LiMnPO,. Paramagnetism is presumed to be placed on normally dia-magnetic atoms by exchanges involving the paramagnetic centre. Some-what similar is the shift 85 in proton resonance in nickelocene, (C,H,)2Ni, ashift many times greater than that in the diamagnetic molecules ferroceneor C5H5Ni*N0.86 The shift in nickelocene is explained 85 if the unpairedelectrons on the nickel spend about half their time on the aromatic rings;0-n interaction 49 is invoked to account for the shift's being towards higherfields (see also ref.37).In high-resolution nuclear magnetic resonance there are many structuraldiagnoses by means of chemical shifts and spin fine-structure. Fluorineresonance is effective in identifying 8' such arrangements as F-O-SO2-F,O=SF,, and F-O-SF, (all grouped fluorine atoms are spectroscopicallyequivalent). The P-H bond is shown to occur in phosphites 88 from phos-phorus resonance, and the covalent P-0-P linkage in the polyphosphates;phosphorus resonances in numerous other compounds have been related tostructure.89 The boron-11 resonance in B,HI1 demonstrates three groupsof boron atoms, and the proton resonance spectrum (simplified by saturation7 6 H.S. Gutowsky and M. Takeda, J . Phys. Chem., 1957, 61, 95.7 7 M. Takeda and H. S. Gutowsky, J . Chem. Phys., 1957, 26, 577. '* J . J. Drysdale and W. D. Phillips, J . Amer. Chern. SOC., 1957, 79, 319.79 P. M. Nair and J. D. Roberts, ibid., p. 4565.81 L. H. Piette and R. A. Ogg, jun., ibid., 1957, 26, 1341; W. D. Phillips, C. E.Looney, and C. P. Smeath, J . Molecular Sfiectr., 1957, 1, 35.82 C. E. Looney, W. D. Phillips, and E. L. Riley, J . Amer. Chew. Soc., 1957,79, 6136.H. S. Gutowsky and C. H. Holm, J . Chem. Phys., 1956, 25, 1228.R. G. Shulman and V. Jaccarino, Phys. Rev., 1957, 108, 1219.84 J .M. Mays, ibid., p. 1090.85 H. M. McConnell and C. H. Holm, J . Chem. Phys., 1957, 27, 314.8 6 T. S. Piper and G. Wilkinson, J . Inorg. Nuclear Chem., 1957, 4, 104.87 F. B. Dudley, J. N. Shoolery, and G. H. Cady, J . Amer. Chem SOC., 1956,78,568.8 8 C. F. Callis, J. R. van Wazer, J. N. Shoolery, and W. A. Anderson, ibid., 1957,79,2719.89 J. R. van Wazer, C. F. Callis, J. N. Shoolery, and R. C. Jones, ibid., 1956, 78,5715; J. R. van Wazer, ibid., p. 5709; N. Muller, P. C . Lauterbur, and J. Goldenson,ibid., p. 3567; J. R. Parks, ibid., 1957, 79, 757.R. Schaeffer, J. N. Shoolery, and R. Jones, ibid., p. 460614 GENERAL AND PHYSICAL CHEMISTRE'.of the boron spins) shows four groups of protons. Boron trifluoride com-plexes can be effectively studied 91 by means of their MR spectra of fluorineand other atoms.Proton resonance offers powerful assistance in thestructural diagnosis of carbohydrate derivatives. 92 A field of future activityis indicated in the measurement 93 of many magnetic resonance spectra forcarbon-13 in its natural abundance.Numerous papers deal primarily with spectral fine structures and theirexplanation. There are plenty of indications of the complexity of theeffects involved, and the difficulties which may attend their chemicalinterpretation. For example, some F-F and F-H spin-spin couplings arenot simply related to the structural separations of the atoms concerned.94Methods of determining the signs of coupling constants have been in-d i ~ a t e d . ~ ~ Deuterium substitution was used 96 in evaluating H-H couplingsin acetylene and methane which, for reasons of symmetry, are not obtaineddirectly. Anderson and McConnell 97 discussed the analysis of spectra forvarious spin systems, and Wilson 98 showed that the application of grouptheory to spin-spin coupling can be taken in part from the theory ofmolecular vibrations. Pople 99 has given particularly illuminating treat -ments of certain proton-resonance shifts.In acetylene, the shift to highfield is accounted for by the paramagnetic effect due to the mixing of theground state with excited states for field components across the molecularaxis. A similar effect, absent from methane, operates increasingly alongthe series NH,, H,O, and HF and largely cancels the opposing effect of ioniccharacter.In aromatic substances, this approach elaborates the conceptof ring-currents induced by fields perpendicular to the aromatic planes ;such currents are responsible for the diamagnetic anisotropy of thesemolecules. The shift to low field in benzene, and details of shifts in numerousfused-ring compounds, are rather satisfactorily accounted for. Pople,Bernstein, and Schneider lo0 also give detailed spectra and relevant theoryfor a number of spin-systems in which chemical shifts and spin-spin inter-actions are of comparable magnitude ; cases include o-dichlorobenzene,pyridine, deuteropyridines, methylpyridines, and azulene. The ring-curren ttheory has been applied to results for other aromatic systems.lo1 Chemical9 1 P.Diehl and R. A. Ogg, jun., Nature, 1957, 180, 1114.93, R. U. Lumieux, R. K. Kullnig, H. J . Bernstein, and W. G. Schneider, J . Avrzer.93 P. C. Lauterbur, J . Chenz. Phys., 1957, 26, 217; C. H. Holm, ibid., p. 707.g4 A. Saika and H. S. Gutowsky, J . Amer. Chew. SOC., 1956, 78,4818; C. M. Shartsand T. D. Roberts, ibid., 1957, 79, 1008.95 G. A. Williams and H. S. Gutowsky, J . Chenz. Phys., 1956, 25, 1288; H. S.Gutowsky, C. H. Holm, A. Saika, and G. A. Williams, J . Amer. Chem. SOC., 1957,79, 4590.9 6 M. Karplus, D. H. Anderson, T. C. Farrar, and 13. S. Gutowsky, J . Chem. Phys.,1957, 27, 597.9 7 W. Anderson and H. M. McConnell, ibid., 1957, 26, 1496.9B E. B. Wilson, jun., ibid., 1957, 27, 60.9 9 J. A. Pople, ibid., 1956, 24, 1111; Proc.Roy. SOC., 1957, A , 239, 541, 550; H. J.Bernstein, W. G. Schneider, and J. A. Pople, ibid., 1956, A , 236, 515.100 H. J. Bernstein, J. A. Pople, and W. G. Schneider, Canad. J . Chem., 1957, 35,65; J. A. Pople, W. G. Schneider, and H. J. Bernstein, ibid., p. 1060; W. G. Schneider,H. J . Bernstein, and J. A. Pople, ibid., p. 1487.101 J. S. Waugh and R. W. Fessenden, J . Amer. Chem. Soc., 1957, 79, 846; G.Hazato, J . Chenz. P h y s , 1957, 27, 605.Chenz. SOC., 1957, 79, 1005SIIERID-IN RBDIO-FREQUENCY SPECTROSCOPY. 15shifts in the ions C,H,- and C,H,+ show some influence of the overallcharge.lo2 The shielding of fluorine nuclei attached to aromatic rings is,not unnaturally, more c0mplex.10~ A further case in which chemical shiftshave been satisfactorily related to the theory of electronic states is incobaltic c0mplexes.l0~ The shifts in cobalt resonance arc related linearly tothe wavelength of the lowest-frequency optical absorption maximum ; thisis the relationship predicted from ligand-field theory lo5 if the shifts are dueto mixing, by the magnetic field, of a low-lying paramagnetic state with theground state.Relations between chemical shifts and molecular and group propertiesare being sought.The screening at o-, m-, and P-protons in monosubstitutedbenzenes has been compared 106 with the orientating effects of substituents.The shieldings of fluorine in substituted fluorobenzenes are correlated lo’with separate inductive and resonance contributions to Hammett’s sigmafunctions of the substituents.Proton resonance shifts in methyl halidesare a linear function of the electronegativities of the halogens,lo8 and shiftsin other methyl derivatives are used to assign an electronegativity sequenceto the attached groups.Several papers concern solvent effects and complex formation. A provedinfluence of the medium on chemical shifts log indicates the need for cautionin the choice of solvent and any internal standard of reference. Complex-formation of olefinic and aromatic substances with chloroform is studiedby measurement of the resonance of the chloroform protons, and the theoryof ring-currents in the aromatic molecules is used to suggest details of theinteraction. Similar studies have been made of chloroform in the presenceof electron donors such as triethylamine.111 Important effects of hydrogen-bonding are observed in the chemical shifts of proton resonances in hydroxylderivatives, the simplest case being the comparison of the shift for water inthe gaseous 112 and the liquid state.A striking movement of the hydroxyl-proton resonance occurs in ethanol solutions as the degree of hydrogenbonding is varied.113 Ilydrogen-bonding shifts in phenol, substitutedphenols, and acetic acid 114 are correlated with known steric, intramolecularand solvent influences.The effectiveness of variousparamagnetic ions in broadening the chlorine resonance in chloride solu-tions115 has been related to the rapidity of solvent exchange around theSeveral studies relate to rates of processes.lo2 J.R. Leto, I;. A. Cotton, and J. S. Waugh, Nature, 1957, 180, 978.lo3 T. Isobe, K. Inukai, and K. Ito, J . Chem Phvs., 1957, 27, 1215.lo4 R. Freeman, G. R. Murray, and K. E. Richards, Pvoc. Roy. Soc., 1957, A , 242,455.lo5 J. S. Griffith and L. E. Orgel, Tram. Favaduy Soc., 1957, 53, 601.lo’ R. W. Taft, jun., ibid., 1957, 79, 1045.lo* A. L. Allred and E. G. Rochow, ibid., p. 5361.lo9 A. A. Bothner-By and R. E. Glick, J . Chem. Phys., 1957, 26, 1647, 1651;110 L. W. Reeves and W. G. Schneider, Canad. J . Chem., 1957, 35, 251.111 G. J. Korinek and W. G. Schneider, ibid., p. 1157.112 R. A. Ogg, jun., Helv. Phys. Acta, 1957, 30, 89.113 A. D. Cohen and C. Reid, J . Chem. Phys., 1956, 25, 790.114 C. M. Huggins, G. C. Pimentel, and J.N. Shoolery, J . Phys. Chem., 1956,115 J. E. Wertz, J . Chem. Phys., 1956, 24, 484.1’. L. Corio and B. P. Dailey, J . Amer. Chent. Soc., 1956, 78, 3043.P. L. Corio and B. P. Dailey, ibid., 1956, 25, 1291.60, 131116 GENERAL AND PHYSICAL CHEMISTRY.paramagnetic ion. Rates and mechanisms of fast protolyses have beenstudied 116 by high-resolution techniques, and chemical shifts have beenused to study equilibria 11' involving methylamines. A number of exchangeprocesses were detected, such as those involving the fluorine atoms in chlorinetrifluoride and iodine pentafluoride,Il8 and in boron trifluoride complexes. 91Proton resonance was applied to water adsorbed on titanium dioxide lI9and to methane on the same adsorbent,120 and related to structural featuresof the adsorbed layers.Further applications of this type are to be expected.Nuclear Quadrupole Resonance.-This field has some resemblance tonuclear magnetic resonance, but complexities associated with the necessityof working with crystalline substances have so far kept chemical interest innuclear quadrupole resonance at a lower level. In the selection of the worknow mentioned, results of predominantly crystallographic interest have beenexcluded. A general review of nuclear quadrupole coupling has beengiven.121Chlorine quadrupole resonances continue to be measured. In (PNC12),and (PNC12), there is evidence122 of two P-C1 distances. In tungstenhexa- and tetra-chloride the low chlorine coupling 123 has led to a suggestedrevision of the nature of the bonds.Chlorine quadrupole resonances inchlorinated heterocylic molecules and (CICN), have been discussed interms of electronic effects; the inductive effect of =NH- in the ring showsas a 10% increase in resonant frequency. Work on all the polychloro-benzenes is complete ; 125 the chlorine quadrupole resonance frequencyacquires increments proportional to the number of substituents ortho to thechlorine. A correlation is indicated between the frequency shifts relative tochlorobenzene and Hammett's sigma functions of substituents. A similarsituation occurs with the bromine quadrupole resonances in polybromo-benzenes.126 Bromine and iodine quadrupole resonances have been measuredin numerous benzene derivatives,12' and also correlated with the sigmafunctions.A series of papers on the halides of aluminium, gallium, and indium isnotable for the variety of types of quadrupole resonance employed.Thebromine resonance in Al,Br, shows 128 the presence of both bridge andterminal bromine atoms, and has been interpreted in terms of ionic characterin the bonds. Similar effects are shown by the iodine resonances in the+iodides of aluminium, gallium, and indium.129 Bromine, gallium,E. Grunwald, A. Loewenstein, and S. Meiboom, J . Chem. Plays., 1957, 27,117 A. Loewenstein and S. Meiboom, ibid., p. 641.11* E. L. Muetterties and W. D. Phillips, J . Amer. Chem. SOC., 1957, 79, 322.llQ J. M. Mays and G. W. Brady, J . Chem. Yhys., 1956, 25, 583.lZ0 N. Fuschillo and C.A. Renton, Nczture, 1957, 180, 1063.121 W. J. Orville-Thomas, Quart. Rev., 1957, 11, 162.122 K. Torizuka, J . Phys. SOC. Japan, 1956, 11, 84; H. Negita and S. Satc123 R. P. Hamlen and W. S. Koski, ibid., 1956, 25, 360.Chem. Phys., 1956, 24, 621.124 G T . <pup1 R C Ramps and P 1 Rrav ihid n 1 R R f i . H. Ncwitn 2nd S-and067.u, J .J' ---.7* " - " - - J r- - - - - 7 0--- ---- -- -. -. "-bv*, --. -. I--u - .Satou, ibid., 1957, 27, 602.125 P. J. Bray, R. G. Barnes, and R. Bersohn, ibid., 1956, 25, 813.127 G. W. Ludwig, ibid., p. 159.lZ8 R. G. Barnes and S. L. Segel, ibid., p. 180.129 S. L. Segel and R. G. Barnes, ibid., p. 578.P. A. Casabella, P. J. Bray, S. L. Segel, and R. G. Barnes, ibid., p. 1280THIRSK: ELECTROCHEMISTRY. 17indium resonances are also reported for gallium bromide and iodide andindium bromide and iodide.130The single iodine resonance in iodine trichloride is thought l3I to be dueto the ion ICl,+ in the structure 1Cl2+ICl4-, the iodine in IC1,- beingexpected to show only small nuclear coupling. The chlorine quadrupoleresonance frequencies in IC1,- and IC1,- are 132 only about half the frequencyin iodine monochloride, and an electronic explanation is suggested.Fine structure in the quadrupole resonance of elementary iodine 133 isinterpreted in terms of electron-coupled spin-spin interaction.The first case of a sharp change in quadrupole resonance frequencyaccompanying a phase transition is reported; 134 in 1 : 2 : 4 : 5-tetrabromo-benzene the bromine resonance frequency changes sharply by 0.15y0, withhysteresis, as temperature is variednear 40” C.ELECTROCHEMISTRY.J.S.SIKCE the last Report 1 a number of books of interest have appeared; twoconcern dipole moments and dielectric behaviour,2a, and there are animportant text on electrolyte solution^,^ a detailed treatment of metalelectrodeposition,* a wide survey at an elementary level,5 and a compilationof essays relevant to electrochemistry in biology and medicine.6 Theproceedings of the 1954 and 1955 meetings of C.I.T.C.E. have beenpubli~hed.~~j The 54th meeting of the Bunsen-gesellschaft was devoted tostudies of electrochemical phenomena at metal electrodes.8 Discussionswere held by the Faraday Society on membrane phenomena 9a and inter-action in ionic solution^.^^ Several reviews of current work on electrolytesolutions leu, a and electrode processes lla, have appeared, one by Delahay 11*130 R.G. Barnes, S. L. Segel, P. J. Bray, and P. A. Casabella, J . Chem. Phys. 1957,26, 1345.131 S. Hagiwara, I<. Kato, Y. Abe, and M. Minematsu, J . Phys. SOC. Japan, 1957,132 C. D. Cornwell and R. S. Yamasaki, J . Chem. Phys., 1957, 27, 1060.l33 S. Kojima, S. Ogawa, S. Hagiwara, Y. Abe, and M. Minematsu, J . Phys. SOC.ls4 F. B. Johnson, Nature, 1956, 178, 590.12, 1166.Japan, 1966,11, 964.J. N. Agar and J. A. B. Randles, Ann. Reports, 1954, 51, 103.( a ) J. W. Smith, “ Electric Dipole Moments,” Butterworths Scientific Publications,London, 1955; (b) C. P. Smyth, “ Dielectric Behaviour and Structure,” McGraw-HillBook Co.Inc., New York, 1955.3 R. A. Robinson and R. H. Stokes, I ‘ Electrolyte Solutions,” Butterworths Scien-tific Publications, London, 1955. * H. Fischer, “ Elektrolytische Abscheidung und Elektrokristallisation von Metal-len,” Springer-Verlag, Berlin, 1954.E. C. Potter, “ Electrochemistry Principles and Applications,” Cleaver-HumePress Limited, London, 1957.“ Electrochemistry in Biology and Medicine,” ed., T. Shedlovsky, Chapman andHall, Ltd., London, 1955.( a ) International Committee of Electrochemical Thermodynamics and Kinetics,6th Meeting, Butterworths Scientific Publications, London, 1955 ; (b) InternationalCommittee of Electrochemical Thermodynamics and Kinetics, 7th Meeting, Butter-worths Scientific Publications, London, 1957.( a ) Discuss.Faruda-v SOC., “ Membrane Phenomena,” 1956, 21; (b) Discuss.Faraduy Soc., “ Interaction in Ionic Solution,” in the press.lo ( a ) 0. Redlich and A. C. Jones, Ann. Rev. Phys. Chem., 1955, 6, 71; ( b ) R. A.Robinson and R. H. Stokes, ibid., 1957, 8, 37.l1 (a) D. C. Grahame, ref. 10a, p. 337; (b) P. Delahay, ref. lOc, p. 229.* 2. Elektrochem., 1955, 59, 59318 GENERAL AND PEYSIC-41, CHEMISTRY.being particularly systematic in its treatment. Frumkin has reviewed workon the effect of adsorption on electrochemical kinetics 12a and on electrodekinetics with the object of showing the close connection with the generalkinetics of chemical reactions in solution.12b Van Rysselberghe haspublished a monograph on the thermodynamics of reversible and irreversibleelectrochemical ~ystems.1~Although the volume of work in electrochemistry is now considerable werestrict this Report essentially to anodic processes, including evolutionof oxygen and phenomena allied to passivation; the latter has receivedlittle attention in previous reviews and reports.In addition some recentstudies on double layers which are particularly relevant to electrode processeshave been included.Oxygen overvoltage hasbeen examined at high current densities on nickel and electroplatedcobalt.14b, With nickel, current densities up to 10 A/cm.2 in 7*5~-potassiumhydroxide were employed, over a temperature range of 0-55" c. Atransmission coefficient, a, of 0.45 was assumed and quite close agreementwas obtained between the calculated and expected value for 2.3RTlaP (ca.61 yo) which indicated a similarity between oxygen and hydrogen dischargesat high current densities.Cobalt was heavily oxidised and, unlike nickel,readily gave a steady overvoltage. A somewhat unusual reaction schemewas suggested to account for the experimental observations on the kineticsof evolution of oxygen on cobalt, involving the formation of hydroxylradicals and atomic oxygen as intermediates. Oxygen overvoltage at anickel anode has also been studied by Mine, Seiyama, and Sakal.15 Limit-ing currents have been determined with platinum, platinised platinum,palladium, palladised palladium, iridium, and gold in B~-sulphuric acid withand without hydrogen present in the solution.16 The depolarisation ofoxygen has been examined as a function of the orientation and structure ofsingle-crystal tin electrodes,17 and on graphite and porous carbon surfaces.l*Oxygen overvoltage was determined in concentrated perchloric acid l9 andin perchloric acid of concentrations up to 9 .8 ~ and sulphuric acid to 1 5 ~ . ~ In the latter work 20a it was concluded that the rate of evolution of oxygendepended on the rate of decomposition of the oxide formed on the surfaceand that the evolution proceeded through formation of an anion. A studyof the r81e of the acid anion is planned with use of oxygen-18. The r6le ofsurface oxides has been investigated with oxygen-18 by Rosenthal andl2 ( a ) A. N. Frumkin, Us@ekhi KJzim,, 1955, 24, 933; ( b ) " Voprosy Khim. Kinetiki,Kataliza, i Reaktsionnoi Sposobnosti," Akad.Nauk S.S.S.R., 1955, p. 402.l3 P. Van Rysselberghe, " Electrochemical Affinity," Hermann and Co., Paris, 1955.l4 (a) Ya. I. Turyan and I. S. Gol'denshtein, Zhur. priklad. Khim., 1956, 29, 379;( b ) Ya. I. Turyan and I. A. Gershlrovich, ibid., p. 600; ( c ) idem, J . Appl. Chem. U.S.S.R.,1956, 29, 69.l5 T. Mine, T. Seiyama, and W. Sakal, J . Chew. SOC. Japan, I n d . Clzem. Sect., 1955,58, 725.l6 XI. Breiter, C. A. Knorr, R. Meggle, 2. Elektrochem., 1955, 59, 153.l7 V. N. Nikulum and S. M. Kochergin, Zhur. fiz. Khirn., 1956, 30, 2337.l9 T. R. Beck and R. W. Moulton J . Electrochem. SOC., 1056, 103, 347.2o ( a ) R. I. Kaganovitch, M. A. Gerowith, and E.Emkeev, Doklady Akad. NaukS.S.S.R., 1956, 108, 101; ( b ) K. I. Rosenthal and V. I. Veselovskii, ibid.. 1956, 111,637: ( c ) M. Anbar and H. Taube, J . Amer. Chein. Soc.,1956, 78, 3252.Anodic Processes.-(a) Evolution of oxygen.N. N. Voronin and 0. V. Izbzkova, Ukifain. Klzirn. Zhur., 1956, 22, 446THIRSK ELECTROCHEMISTRY. I9Veselovskii,20b who examined the reaction on what they described as aPtO-type oxide, formed a t 0.8-1-2 v, and one of PtO[O], type formed at1-3-1.5 v in N-sulphuric acid. Oxygen-18 was evolved from the latterearly in the electrolysis but the platinum oxide remaining did not participatesubsequently. The fractionation of isotopes of oxygen at anodes wasexamined by Anbar and Taube.,Oc The isotope fractionation factor foroxygen from water depended on the electrode material and was determinedon nickel, iron, palladium, cobalt, copper, manganese, silicon, tin, gold,silver, platinum, lead, and carbon.The range of discrimination was from0.35% for tin to 1-8 for iron, and over a limited range was independent ofcurrent density and almost independent of the acidity or basicity of theelectrolyte. They suggest that the overall isotope discrimination liesin the exchange reaction M-OH + H20* ---+ M-*OH -+ H20 and kineticdiscrimination in the succeeding step of formation of an oxygen-hydroxylgroup bond. Once this bond is formed they assume that the peroxide willlead unidirectionally to O,, and that, for certain metals at least, the rate ofevolution of oxygen is determined by formation of an -0-O- bond, ratherthan the M-OH bond as suggested by Delahay.21c With lead dioxide andmanganese dioxide deposits none of the lattice oxygen appears as oxygenmolecules.Izgaryshev and Yefinov 21a investigated the dependence of thekinetics of oxygen evolution on smooth platinum on sulphuric acid con-centration and the degree of oxidation of the platinum.21b They suggestthat the divergence of results by different operators depends on the degreeof preliminary anodic polarisation of the electrode, and they determinedthe effect of this on the Tafel slope " b ". Pre-polarisation for 1 min.changed b from 0.156 to 0.115 for all acid concentrations; it remainedconstant after 15 min., but " a " shifted to higher potentials. Theyconsidered that the formation and decomposition of a platinum-oxidecombination at the surface was an essential stage in the process of theelectrochemical evolution of oxygen.The longer the preliminary polaris-ation the stronger the Pt-0 bond and the greater the overpotential. Theresult seems to be somewhat at variance with the theoretical study byRuetschi and Delahay,21c unless interpreted as relating the overvoltagewith the degree of oxidation. Ruetschi and Delahay state that thevariations in overvoltage arise primarily from variations in the energy of theM-OH bond, which they calculate, but decrease approximately linearlywith increasing bond energy. This was verified by them by using Hicklingand Hill's data 21d for silver, gold, cadmium, cobalt, copper, iron, nickel,cobalt, lead, palladium, and platinum polarised in N-potassium hydroxide.There was no correlation between oxygen overvoltage for different metalsand the corresponding work functions.The effect of surface-active additives on the oxygen overpotential onsmooth platinum was investigated by Kheifets and Rivlin.22 Bockris 23a21 ( a ) N.A. Izgaryshev and E. A. Yefinov, Zhur. $2. Khim., 1956, 30, 1807; ( b )idem, ibid., 1606; ( c ) I>. Ruetschi and P. Delahay, J . Chew. Phys., 1955, 23, 556; ( d )A. Hickling and S. Hill, Discuss. Faraday Soc., 1947, 1, 236.22 V. L. Kheifets and I. Ya. Rivlin, Zhur. pyiklad. Khim., 1956, 29, 69.23 (a) J. O'M. Brockris, J . Chew. Phys., 1956, 24, 819; (b) J. A. Christiansen, Z .phvs. Cheni., 1936, B, 33, 145; 1939, 37, 37420 GENERAL AND PHYSICAL CHEMISTRY.employs the Christiansen relations 2a to obtain expressions for the kineticsof an electrode process containing any number of intermediate steps; themethod was applied to oxygen evolution.This approach is of interest, butof value only if the Christiansen relations are justifiably employed. Bockrisand Huq studied oxygen evolution, by the constant-current method, onbright platinum electrodes in ultra-pure sulphuric acid in the absence andpresence of sodium sulphate. The overall anodic reaction is confirmed as40H- - 4e __t 0, + 2H20. Experiments were carried out on theattainability of the reversible oxygen electrode. A steady potential of1.24 & 0.03 v was observed in solutions with less than 10-11 mole/l.ofimpurity i.e. by extrapolation to zero current and identified with the thermo-dynamically calculated reversible potential for the overall reaction 0, + 2H,O + 4e Evidence is produced that the rate-controlling step isdischarge of OH- or H,O.A.C. methods were employed by Becker and Breiter 25a to study oxygenevolution on platinum in sulphuric acid and alkali solutions. Over thepotential range 0.4-2v a value of 10-80 pF/Cm.' is quoted for thepredominantly capacitative A.C. impedance, and this is ascribed to theslightly frequency-dependent capacity of the double layer. The voltage-capacity curve showed two maxima, indicating that the composition of thedouble layer is strongly affected by adsorption of oxygen, which is directlydemonstrable by cathodic charging curves.Impedance measurements werediscussed in connection with a determination of anion adsorption.25bEvaluation of the charging curve in O-G~-sulphuric acid at a cathodic currentdensity of 0.1 A/cm.2 suggested a coverage of the electrode by oxygen whichincreases continuously above 0-8 v. A roughness factor of 1.5 being assumed,the presence of a monatomic PtO layer is deduced at 1.4 v, and a diatomiclayer at 2.1 v, in the region of oxygen evolution. Balashova 256 investigatedmore particularly adsorption of anions (S042-) on a platinised-platinumsurface; the experimental method was described in detail. The activity ofelectrode and solution was determined by using H235S0, and the resultsindicated the coexistence of a rapid adsorption of sulphate ion on theplatinum surface with a slow process caused by the ions' interacting withthe surface.The effect of alternating current on anodic processes with platinumelectrodes was studied theoretically by Llopis and Colom,26 and Praeger 27measured the A.C.impedance of a platinum electrode in alkali halidesolutions as a function of polarising voltage and frequency. The behaviourof aluminium, chromium, hafnium, niobium, tantalum, vanadium, titanium,and zirconium anodes at very low current densities before oxygen is evolvedwas examined by H. A. Johansen et aZ.28The complexity of40H-.(b) The formation of oxides and insoluble salts.24 J. O'M. Bockris and A. K. S. Huq, Pvoc. Roy. SOC., 1956, A , 237.277.25 (a) M. Beckerand M. Breiter, 2. Elektrochem., 1956, $0, 1080; (b) N. A. Balashova,26 J. Llopis and F. Colom, Anales Fiz. Quim., 1955, 51, B, 379.2 7 M. J . Praeger J. Electrochem. Soc., 1957, 104, 454.28 H. A. Johansen, G. B. Adams, and P. Van Rysselberghe, J. Eleckochem. SOC.,Doklady Akad. Nauk S.S.S.R., 1955, 103, 639.1957, 104, 339THIRSK : ELECTROCHEMISTRY. 21anodic processes of this kind has made them a less attractive experimentaland theoretical study than, for example, the cathodic phenomena ofhydrogen evolution and metal deposition, or even oxygen overvoltage.Earlier methods of investigation led to a situation summarised byW. J. Miille1-.~9 Development in ideas of semiconduction in inorganicmaterials and the increasing use of structural techniques are helpful informulating more reliable models of the various systems that may beencountered. This, together with the introduction of a wider variety ofelectrochemical techniques, is leading to progress in the study of thesedifficult problems.This is of considerable value in view of the importanceof these systems to electrochemical cells and corrosion.Thermodynamic studies defining the regions for the existence andcoexistence of deposits on metal electrodes and the ions in solution havebeen studied extensively by Pourbaix and his collaborators ; the principlesand methods involved have been described,30 and many of the newer datafor a variety of systems are in the publications of the Centre Belge d'gtudede la Corrosion and in the C.I.T.C.E.proceedings.Some advances in the study of the mechanism of anodic oxide formationwith high fields can be illustrated by work on aluminium, tantalum, niobium,and an antimony-indium alloy. Much use has been made in the interpret-ation of these anodic studies of a theory of oxidation advanced by Cabreraand M ~ t t , ~ l and later extended by Dewald 32 to include the effect of a space-charge in the oxide. Cabrera and Mott assumed that every ion escapingfrom the metal is swept right through the oxide by the high field applied andthat a single barrier at the metal-oxide interface controls the current andhence the rate of growth. Consequently the Tafel slope (6E/6 In i)T whereE is the field should be directly proportional to T , the absolute temperature,and inversely proportional to the product of the charge on the ion and thebarrier half-width. Young 33a examined films formed with a constantcurrent on niobium between 0" and 90" with a field strength of the order of106v/crn.and stated that the Tafel slope is independent of T. A similarresult for tantalum was obtained by V e r m i l ~ e a . ~ ~ ~ Jacobs,34 however,reported that in non-aqueous solvents the Tafel slope does fall off in therange 0" to -63". These results are all interpreted in terms of Dewald'stheory. It was pointed out that the effect of the space-charge causes achange from control at the metal-oxide interface to control by migrationas T increases; at low and high temperatures respectively the Tafel slopeshould be proportional to T , and at intermediate temperatures such as thoseemployed by Young the variation with T is too slight to be detected.Inthe case of niobium Young considered that there was evidence for aZ g W. J. Muller, " Die Bedeckungstheorie der Passivitat der Metalle uad ihre3O M. Pourbaix, " The Thermodynamics of Dilute Aqueous Solutions," English31 N. Cabrera and N. F. Mott, Rep. Pvogr. Physics, 1949, 12, 163.32 J . F. Dewald, J . Electrochem. Soc., 1955, 106, 1.33 ( a ) L. Young, Trans. Faraday Soc., 1956, !52, 502, 515; ( b ) D. A. Vermilyea,34 W. M. Jacobs, Discuss. Faraday Soc., "Molecular Mechanisms of Rate Pro-experimentelle Begrundung," Verlag Chemie, Stuttgart, 1934.translation by J. N. Agar, Edward Arnold and Co., London, 1949.Acta Metallurgica, 1953, 1, 282.cesses in Solids," 1957, 23, 22022 GENERAL AND PHYSICAL CHEMISTRY.space-charge effect ; also, the observed dependence of space-charge on currentdensity corresponded to the case in Dewald’s theory in which the “ jump ”distance for diffusion into the oxide was less than for diffusion through theoxide..The data were explained with reasonable values for all parametersexcepting that the jump distances were of the order of 6-8 A and thereforetoo large; it was suggested that polarisation forces affect the field strength.The formation of oxide on tantalum has been studied extensively byVermilyea;35 the oxide film was formed even when the metal was heldnegative to hydrogen; 35a the activation energy for formation of Ta20,is not a single linear function of the applied field; 35b and capacitancemeasurements did not give an unambiguous decision concerning thn,presence of a ~pace-charge.~~~ Although a mechanism for the growth wassuggested,35b the nucleation process was not satisfactorily explained.D e ~ a l d , ~ ~ using zone-refined crystals of an antimony-indium alloy, showedthat the oxidation rate in 0-1N-potassium hydroxide depended markedlyon the crystal face.At low fields (111) and (332) faces oxidised more thanten times as quickly as (110), ( i l l ) , and (332) faces. At high fields all facesoxidise at the same rate; the data were interpreted in terms of the detailedstructure of the alloy and the theories of oxide growth referred to.31932Pronounced crystallographic effects observed at low fields and their absenceat high fields establish the location of the rate-limiting process. At lowfields passage into, and at high fields passage through, the film is the difficultstep.The oxides formed had an approximately 1 : 1 indium : antimonyratio in spite of the solubility of Sb,03 in the electrolyte. The experimentalresults throw doubt on a simple interstitial-ion transport mechanism.The anodic dissolution of semiconductors of controlled electricalproperties is of great interest and both germanium and silicon have beeninvestigated. A large voltage barrier was observed at about 0 * 8 m ~ / c m . ~at room temperature on the %-type but not the $-type germani~m.~’ Thisvoltage barrier, of 3 ohms cm.-1, broke down at about 0 v in manyelectrolytes.During dissolution the surface appeared to be covered withapproximately a monolayer of oxide or hydroxide. The mechanismsuggested for the anodic dissolution involved two holes and two electronsfor each germanium atom dissolving. With silicon the oxide was formed byanodisation in potassium nitrate solutions with N-methylacetamide as solvent .38With use of more conventional electrodes, a wide variety of anodicphenomena are revealed by studies with silver, mercury, lead, and nickeland all these metals have continued to be investigated in detail.Theanodic formation of the halide layer on polycrystalline silver in hydrochloricacid and rearrangement phenomena on reduction were examined by Jaenickeet al.; 39 elsewhere,40 the primary object was to establish a reliable techniqueSilver has been investigated in both acid and alkaline solutions.35 (a) D. A. Vermilyea, J . Electrochem. Soc., 1954, 101, 389; ( b ) 1955, 102, 207;36 J. F. Dewald, ibid., 1957, 104, 244, 257.37 D. R. Turner, ibid., 1956, 103, 252.39 W. Jaenicke, R. P. Tischer, and H. Gerischer, 2. Electrochem., 1955, 59, 448.40 M. Fleischmann, J. Sowerby, and H. R. Thirsk, Trans. Faraduy SOL, 1957,53,91.( c ) ibid., p. 655; ( d ) ibid., 1956, 103, 690; ( e ) 1957, 104, 140.P. F. Schmidt and W. Michel, ibzd., 1957, 104, 230THIRSK: ELECTROCHEMISTRY. 23for preparing surfaces containing single-crystal faces for subsequent anodis-ation; a phenomenon of cathodic smoothing was observed and optimumsmoothing conditions were determined for reproducibility during the anodicstage Ag _+ AgC1.Pospelova et aZ.41 observed that the oxides producedelectrochemically were less stable than those arising from direct oxidation.The behaviour of silver 42 in sulphuric acid closely resembles that of thelead-sulphuric acid system ; for example, oxidation proceeded by the stagesAg I t was thought that the Ag,O whichwas present was formed by decomposition of AgO together with traces of 3cubic sub-oxide, postulated from crystallographic evidence. It appearsthat in some ways gold behaves rather like silver; there is evidence 43 thatgold polarised in O-lN-sulphuric acid, in a phosphate buffer of pH 6.8, andin 0.1 M-sodium carbonate, has three oxidation steps, Au 4 Au,O--+AuO -+- Au,O,; In potassiumhydroxide solutionsM the stages in oxidation appear to be Ag-A g , O d A g O and analogy is again shown with the lead-lead sulphatesystem in that the Ago is formed primarily from the first formed passivatinglayer (Ag,O), siiice subsequent formation of Ago proceeds at an efficiencyof <1%.The reproducibility of the Tafel slope for evolution of oxygen onthe higher oxide was fair, giving a = 0-39 & 0.01.The dissolution of mercury at very low current densities has been studiedby a new technique 45 and a rate constant for dissolution of 0.476 cm. sec.-lis reported. The initial stages in the anodic formation of calomel have beenstudied in detail by Dibbs et u Z ., ~ ~ with interesting additional evidence (seeref. 47) for the production of a " metastable " high-energy form of calomelbefore '' rafts '' of calomel are formed. The crystallographic structure ofanodically-formed films of mercurous chloride and bromide has been workedout in considerableThe passivation of lead was cxamined by using increments of appliedvoltage in 40.50, 22-80, and 2.99~-solutions of phosphoric acid 49 and it wasconcluded that the passivating layers formed were, progressively, leadphosphate (unspecified) -+- PbO __t PbO, followed by evolution ofoxygen. With the current constant, the overall steps in the anodepotential-time relations can be explained in terms of the stepwise oxidationof Pb to Pb4+. In contrast, Briggs and Wynne-J~nes,~~ investigating thepassivation of lead in halide solutions by electrochemical and opticalmethods, found that the electrochemical formation of compounds on theelectrodes, other than halides (PbCl,, etc.), was rare except in thc case of41 I.N. Pospelova, A. A. Rakov, and S. Ya. Pshezhetskii, ZFzuv. $2. Khinz., 1956,30, 1433.42 P. Jones and H. R. Thirsk, Trans. Faraday SOC., 1954, 50, 732.43 S. E. S. El Wakkad and A. M. Shams El Din, J., 1954, 3098.44 P. Jones, H. R. Thirsk, and W. F. K. Wynne-Jones, Trans. Favaday SOC., 1956,45 S. E. S. El Wakkad, T. M. Salem, and S. E. Khalafalla, J . , 1955, 1702.4 6 H. P. Dibbs, D. J. G. Ives, and R. W. Pittman, J., 1957, 3370.4 7 S. Hillsand D. J . G. Ives, J., 1951, 311.4 8 H. R. Thirsk, Proc.Phys. SOC., 1953, B, 66, 129; E. H. Boult and H. R. Thirsk,J. Kanecki, Z. Zambura, and J. Trau, Bull. Acad. polon. Sci. Classe 111, 1955,3, 37.5 0 G. W. D. Briggs and W. F. K. Wynne-Jones, J., 1956, 2966.Ag,SO, -+ Ago + O,(g).formation of AuO, was not suspected.52, 1003.Trans. Faraday SOC., 1964, 50, 40424 GENERAL AND PHYSICAL CHEMISTRY.potassium iodide solutions, and evidence for a passivating oxide layer wasvery slight.Reactions in the lead-N-potassium hydroxide system were shown toproceed51 in the stages (i) Pb-PbO, (ii) PbO--+PbO, + someoxygen, (iii) predominantly oxygen evolution. Linear portions of the plotof overpotential against In (current density) for oxygen evolution gavecc = 0.5 for the Tafel slope. The anodic formation of lead sulphate in the lead-sulphuric acid system and subsequent oxidation to lead dioxide were examinedkinetically, in some detail, by use of a new method with step-wise increase inthe controlled o~ervoltage.~~ Rate constants for the rate of nucleation andthe rate of growth were determined for the phase change PbSO, --+ PbO,.The actual structure of electrochemically formed lead dioxide is stillreceiving attention and earlier work 53 in which a second, rhombic form wasdescribed has received additional confirmation by Butler.54 Bode andV O S S ~ ~ also report rhombic PbO, together with the usual tetragonal 8modification in the positive electrode of the accumulator and show itsstructure to be related sterically to the red form of PbO and to lead; form-ation of the p form is favoured by high acidity, as confirmed by s.J. €301~.56The deposition of the oxides from nitrate, acetate, and perchlorate solutionsunder conditions of controlled overpotential has been investigated byFleischmann and Liler.57 In this work the effect of pH, lead-ion con-centration, and neutral salts on the kinetics of nucleation and the growth ofthe oxide centres has been measured and the relative incidence of the twoforms of the oxides has been clarified.Nickel has been studied in both acid and alkaline solutions. Thechemistry of the nickel hydroxide-oxide system is particularly hfficult.Trumpler and Saxer 58 worked with nickel anodes in sulphuric acid solutions(N and 5 ~ ) and with dilute ( 0 . 2 ~ ) sulphuric and nickel sulphate solutionscontaining O-O5~-nickelous chloride. In dilute sulphuric acid containingchloride ion there is a potential barrier above which a current peak showsthe end of passivation.Landsburg and Hollnagel 59 measured passivationtimes in sulphuric acid solutions with improved reproducibility by previouslyreducing the nickel at 500" in hydrogen. Acid concentration and theoccluded hydrogen considerably influence the nature of the passivation.Treatment of the metal at different temperatures changes the effectiveanodically active surface, the passivated surface probably being an oxygen-containing compound. Oxygen is evolved on the completely passivatedsurface produced at a sufficiently high pH. Pomosova and Gurevich 6oexamined the effect of chloride ions on the dissolution of nickel anodes.61 P.Jones, H. R. Thirsk, and W. F. K. Wynne-Jones, T r a m . Faraday Soc., 1956,52 M. Fleischmann and H. R. Thirsk, ibid., 1955, 57, 71.53 I. Zaslavskii, Y. D. Kandrashov, and S. S. Tulkachev, Doklady Akad. Nauiz54 G. Butler, personal communication.5 5 H. Bode and E. Voss, 2. Elektrochem, 1056, 60, 1053.5 6 S. J . Bone, Ph.D. Thesis, University of Durham, 1957.5 7 M. Fleixhmann and M. Liler, Trans. Faraday Soc., in the press.5 8 G. Trumpler and W. Saxer, Helv. Chim. Acta, 1956, 39, 1733.59 R. Landsburg and M. Hollnagel, 2. Elektrochem., 1954, 58, 680; 1956, 60, 1098.6 o A. V. Pomosova and L. T. Gurevich, Zhur. priklad. Khim., 1956, 29, 1372.52, 1004.S.S.S.R., 1950, '75, 559THIRSK : ELECTROCHEMISTRY.25Conditions for forming reproducible nickel hydroxide electrodes havebeen examined 62a together with their behaviour in potassium hydroxidesolutions. The coulombic efficiency can approach 100% and the oxidationproceed to NiO,.,; a reduction to NiO,.,, is only possible with the thinnestlayers. Analysis of the oxide layers suggested a composition gradientto account for the divergence between open-circuit potentials and the ratioof 0 : Ni available for reduction. An electrode of nickel with a layer offreshly prepared nickelous hydroxide can be oxidised easily but after ageingonly with difficulty; on nickelous oxide there seemed to be only a surfacereaction.61c Briggs 62 has examined structural modifications in depositedp-NiO*OH brought about in the presence of different cations (K, Na, Ba,Sr, and Ca) in the forming electrolyte, a nickel salt solution buffered byacetate.The behaviour of iron has been studied under a wide range ofconditions. Bonhoeff er and his collaborators examined the effect of acidconcentration,639 e4 anodic diss0lution,6~ and kinetics in acid neutral andalkaline solutions.66 The kinetics have also been studied in the presence ofsulphate ions 67 and phosphoric acid e8 and, with particular reference topassivation, in oxalic and acetic acid and their sodium salt solutions, and inthe presence of sulphate and chloride i0ns.6~ The effect of inhibitor^,^^acceleration of the dissolution by ferric ions,'l passivity in 73 andthe effect of alkaline mono- and poly-sulphides have been considered.Makrides et al.have also made kinetic studies.74 The potentials of passiveiron have been i n t e r ~ r e t e d , ~ ~ the impedance of the layer on passive iron innitric acid has been measured,76 and the potential differences within thepassivated layer 7 7 and the relations between ionic current and the internalpotential discus~ed.~~ Combined A.C. and D.C. measurements have beeninterpreted by electrical circuit analogue methods. 79The nature of the passivating layer on aluminium has been examined insulphuric acid solutions,sO as affected by iron at grain boundaries,sf and61 (a) G. W. D. Briggs, E. Jones, and W. F. K. Wynne-Jones, Trans. Faraday Soc.,1955, 51, 1433; (b) E. Jones and W. F. K.Wynne-Jones, ibid., 1956, 52, 1260;(c) G. W. D. Briggs and W. F. K. Wynne-Jones, ibid., p. 1272.62 G. W. D. Briggs, J., 1957, 1846.63 K. F. Bonhoeffer and K. E. Heusler, 2. phys. Chem. (Frankfurt), 1956, 8, 390.64 K. G. Weil and K. F. Bonhoeffer, ibid., 1955, 4, 175.65 K. F. Bonhoeffer and K. E. Heusler, 2. Elektrochem., 1957, 61, 122.66 K. F. Bonhoeffer, ibid., 1955, 56, 594.87 M. Serra and S. Feliu, Anales F k Quim., 1954, 50, B, 937; W. H. Wade and N.6 8 J. Kameski and 2. Sambura, Bull. Acad. polon. Sci., Cl. 111, 1956,4,107; Roczniki69 M. Serra and S. Feliu, Anales Fis. Quim., 1955, 18, 395, 401, 405.70 E. Rau, Diss. Abs., 1956, 16, 331; C. V. King and E. Rau, J . Electrochem. Soc.,71 H. C. Gatoo, ibid., p. 286.72 K. J. Vetter, 2. Elektrochem., 1955, 59, 67.73 M.Stern and R. M. Roth, J . Electrochem. Soc., 1957, 104, 390.74 A. C. Makrides, N. M. Komodros, and N. Hackerman, ibid., 1955, 102, 363.75 M. J. Pryor, ibid., p. 163.76 L. Gougerot and R. Alfieri, J . Chim. filzys., 1955, 52, 382.7 7 K. I. Vetter, 2. phys. Chem. (Frankfurt), 1955, 4, 165.78 K. G. Weil, 2. Elekfvochem., 1955, 59, 711.79 H. J. Engell and B. Illschner, ibid., p. 716.8 o I. V. Kratoo, Zhur.fiz. Khim., 1954, 28, 1450.81 T. Murakawa, J . Electrochem. Soc. Japan, 1956, 21, 18.Hackerman, Trans. Faraday Soc., 1957, 53, 1636.Chew., 1957, 31, 185.1956, 103, 33126 GENERAL AND PHYSICAL CHEMISTRY.by pH changes and chloride and nitrate ions.S2 Overvoltage for dissolutionof copper in 0.1M-perchloric acid has been related to a calculated rate constantby El Wakkad et aZ.; 43 the rate constant of 3-6 x cm.set.? is to becompared with the value of 4.5 x cm. sec.-l obtained by a differentmethod.83 In concentrated phosphoric acid it has been concluded that thestep Cu __t Cu2+ is rapid, Cu + Cu2+ __t 2Cu+, slow.@ Anodic studiesin solutions of cyanide, chloride, and thiosulphate ions giving stable coppercomplexes show 85 that the primary electrode process is Cu _t Cu+ + e.Goswami,86 using (1 10) single-crystal faces in alkaline solutions, states thata porous Cu20 layer is first formed followed by an outward migration ofcopper ions.Single crystals of hafnium in nitric acid show that the growth depends onorientation of the substrate and that the layers become discontinuous as theacid concentration increases from 70% to Chromium 88 and zinc 89both show a complex anodic behaviour but without additional features ofgeneral interest.The Electrical Double Layer and Related Problems.-The determinationof the potential of the electrocapillary maximum is necessary for anadequate study of reactions taking place on the conductor-solution inter-face ; experimental methods have been reviewed.Several determinationshave been made recently on materials other than mercury. The zero-charge potential at a lead dioxide electrode has been determined by acapacitance 92 and also by a pendulum hardness method 93a described byVenstrem et aZ.,93b who discussed the results of other investigator^.^^^ Themeasurements by the first procedure were carried out in 0.01~- and N-sulphuric acid and N-oxalic acid on lead dioxide plated on gold; the recordedpotential was 1 .8 0 ~ versus the normal hydrogen electrode. The phaseshift was high at frequencies above 1000 c./sec., indicating that polarisationhad little effect on the measured impedance, but, after strong anodic polaris-ation, the oxygen discharge potential became inore negative, indicating theeffects of adsorption. The pendulum hardness method, which can be usedin concentrated solutions, gave a zero-charge potential in O-lN-sulphuric82 A. R. Tourky, E. M. Khairy, and hf. K. Hussein, J . Chinz. phys., 1956, 53, 433.133 J. B. Randles, Trans. Faraday Soc., 1952, 48, 137.84 D. Laforgue-Kantzer, J . Chinz.phys., 1955, 52, 314.85 D. J. Rogers, J. Kleinberg, and A. W. Davidson, J . Inorg. Nucleav chem., 1957,86 A. Goswami, J . Sci. Ind. Res., India, 1956, 15, B, 340.87 R. A. Misch and E. S. Fisher, J . Electrochem. Soc., 1956, 103, 153.8 8 T. Heumann and W. Rosenor, 2. Elektrochem., 1955, 59, 722; I. M. Issa andH. Khalifa, J . Indian Chem. SOL., 1956, 33, 465, 471; I. M. Issa, H. Khalifa andI. A. Ammar, J . Phys. Chenz., 1955, 54, 592; Ya. M. Kolotyrkin and V. M. Knyazhiva,ZJaur. $2. Khirn., 1956, 30, 1990.89 T. Inone, M. Sato, and R. Ishii, J . Electvochem. Sac. Japan, 1954, 22, 679;T. P. Dirkse, J . Electrochem. Sac., 1955, 102, 497; M. Schwabe, Metalloberjlache, 1957,37, 1.91 B. N. Kabanov, I. G. Kiseleva, and D. T. Leikis, Doklady Akad. Nauk S.S.S.R.,1955, 99, 805.O2 M.A. Vorsina and A. N. Frumkin, ibid., 1939, 24, 918.93 (a) D. I. Leikis and E. I<. Venstrem, ibid., 1957, 112, 97; (b) E. K. Venstrem,V. I. Likhtman, and P. A. Rehbinder, ibid., 1956, 107, 105; (c) J. O’M. Bockris andR. Parry- Jones, Nature, 1953, 171, 930.4, 115.A. N. Frumkin, 2. Elektrochem., 1955, 59, 507THIRSK : ELECTROCHEMISTRY. 27acid within 0.1 v of the above (1.9 v vs the normal hydrogen electrode) butin 8N-sulphuric acid the potential was displaced towards 1.7 v because ofadsorption. The more marked asymmetry of the plots of hardness againstpotential in the dilute solutions at positive potentials was tentativelyassociated with change in surface structure and an increase in area due toadsorption. The precise crystallographic form of the PbO, was not stated;it could have been either the cc or more probably the form and it would beof interest to seek for differences in the electrocapillary maxima of thesetwo modifications.The bubble method has been employed by Ukshi and Levin 94 inpreliminary measurements to establish the zero-charge potential on copperand chromium. From the preliminary results it was considered that thevalue lay between 0.07 and 0-02 v for copper and 0.02~-0.04 v for chromium.In this particular case the information was sought in connection with theeffects of anions during electrodepo~ition.~~ The figure for copper does notagree particularly well with the value quoted in a very interesting paper byKheifets and Kra~ikov,~6 who studied the effect of pH on the zero-chargepotential of a large number of metals.They used an A.C. method tomeasure capacitance over a wide range of frequency and decided that metalsfall into two groups: those which do not absorb hydrogen and for whichthe zero-charge potential is independent of pH (Zn, Cd, Hg, Ag, and Cu),and those absorbing hydrogen and for which there is a marked pHdependence (Fe, Ni, Co, Pd, and Pt). A further investigation concerningthe validity of these results would be of great interest; for example, in viewof the cathodic ,behaviour of single crystals of silver *O it seems possible thatthe behaviour of some of the metals in the first group was rather a functionof their crystalline state than a fundamental difference in behaviour.According to Ruetschi and Delahay 97 the potential of zero charge withrespect to a reference electrode varies linearly with the work function for anideal polarised electrode whilst this potential for a reversible electrode isindependent of the nature of the electrode.This is confirmed from theliterature ; they include in the first class silver, cadmium, copper, gallium,mercury, nickel, lead, and platinum and in the second class thallium,silver, gold, copper, mercury, and platinum. For perfectly polarisedelectrodes the difference between the Volta potentials from electrode tosolution at zero charge is ca. -0.33 v. The difference between the Galvanipotentials is equal to the surface potential of the electrode. For areversible electrode, diff erences of Volta potentials at zero charge varylinearly with the electronic work function.Oel and Strehlov 98 also statethat there are two potentials at which a metal is uncharged; one impressedon the electrode by polarisation, the state being characterised by a maximumin the surface tension-the Lippmann potential; the other at unpolarisedelectrodes established by transfer of potential-determining ions-the Billiter94 E. A. Ukshi and A. I. Levin, DokEady A k a d . Nauk S.S.S.R., 1955, 105, 119.95 A. I. Levin and E. A. Ukshi, ibid., 1953, 89, 1045.g6 V. L. Kheifets and B. S. Krasikov, ibid., 1956, 109, 586.9 7 P. Ruetschi and P. Delahay, J . Chem. Phys., 1955, 23, 697.H. J. Oel and H. Strehlov, 2. phys. Chenz. (Frankfurt), 1954, 1, 241; and par-ticularly idem, ibid., 1955, 4, 8928 GENERAL AND PHYSICAL CHEMISTRY.potential. Experimental results given in the literature are discussed.Anoverall impression gained from papers containing such speculations is thata really thorough and critical examination of published experimentalresults, particularly from early sources, is very necessary. Grahameet aLS9 examined the impedance of lead and tin electrodes by employing the“ frozen drop ” method.l0*9 The dispersion of capacity was small anddepended on the smoothness of the surface; the dispersion of resistance wasmuch larger and was independent of the potential, showing that one is notdealing with Faradaic admittance. The dependence of capacity on potentialroughly parallels that of mercury.The possible effect of water moleculeson the behaviour of the capacity of the double layer at mercury-solutioninterfaces as a function of frequency was examined by Bockris et aZ.lol Theexperimental results can be interpreted if it is assumed that the motion ofthe water molecules that are absorbed on the electrode is so restricted thattheir relaxation time is large enough to fall within the frequency range ofmeasurement.There have been several very interesting contributions to the problemof the specific adsorption of ions and also the anomalous displacement ofthe potential of the electrocapillary maximum on mercury with change inactivity of the surface-active anion-the Esin and Markov effectGrahame has extended the analysis of the problem advanced by Ershler 102bin which allowance is made for the discreteness of the absorbed ionic chargetogether with multiple reflections within the double layer.This treatmentis presented in two papers; the first 103a theoretical, the second containingimportant new experimental r e ~ u l t s . 1 ~ ~ ~ Ershler’s results are confirmedand extended and in addition equations are developed connecting thepotentials within the inner region of the double layer with experimentallyaccessible data. Parsons lo4 derives an adsorption isotherm for specificallyadsorbed ions and demonstrates that Stern’s use of the Langmuir model isincorrect. The use of an empirical isotherm based on a virial type ofequation of state with a square-root term and the Amagat isotherm lead toagreement with experiment.In Parsons’s later paper lo5 on the Esin andMarkov effect this thermodynamic approach is developed and it is shownthat the effect can be obtained not only at the electrocapillarity maximumbut at any point in the electrocapillary curve. An empirical equation of thesame form as the Temkin isotherm lo6 is satisfactory for moderate coverageof adsorbed anions. The new results obtained by Grahameloa withgg D. C. Grahame, R. E. Ireland, and R. C. Petersen, Technical Report t o 0. N. R.1956, No. 22.l o 0 T. Borisova, 33. V. Ershler, and A. N. Frumkin, J . Phys. Chern. U.S.S.R., 1948,925; T. Borisova and B. V. Ershler, ibid., 1950, 24, 337.lol J. O’M. Bockris, W. Mehl, B. E. Conway, and L. Young, J .Chem. Phys., 1956,25, 776.Io2 ( a ) 0. A. Esin and B. F. Markov, Acta Physe’cochim. U.S.S.R. 1939, 10, 353;( b ) B. V. Ershler, J . Phys. Chem. U.S.S.R., 1946, 20, 679.l o 3 ( a ) D. C. Grahame, Technical Report to the 0. N. R., No. l., 1957; ( b ) idem,ibid., No. 5, 1957.1°4 R. Parsons, Tmns. Furaduy SOC., 1955, 57, 1578.lo5 Idem, Proc. 2nd Internat. Congres on Surface Activity, vol. 3, London, 1958.lo8 M. I. Ternkin, Zhuv. fiz. Khim., 1941, 15, 296; S. Brunauer, J . Amer. Chem.Soc., 1942, 64, 757THIRSK : ELECTROCHEMISTRY. 20the mercury-potassium iodide system permitted detailed calculations,suggested previously,lo1 and a further development in the theory. Grahameconfirms Parsons's suggestions for the relation between the surface excessof specifically adsorbed anions, d, and log a, although he found that theisotherms could not be superimposed by displacement along the log a, axis.In addition the differential capacity related to the inner region of the doublelayer, measuring the capacity of that region under conditions such that theconcentration of adsorbed ions within it remain constant, gives valuespractically independent of d.If this capacity C" is independent of ni thenit should be independent of the identity of the anion as well, since in thelimit when ni = 0 the identity of the anion can make no difference. Plotsof the differential capacity for the inner region for potassium fluoridetogether with C for potassium iodide were made and, at negative valuesof the charge, the curves were identical and for positive values the agree-ment was still almost within the limits of experimental error.The remark-able conclusion from these calculations is that the field generated by theadsorbed anions has little effect upon the capacity of the inner region. Thisconstant value of C" enabled Grahame to calculate essentially completelythe properties of the inner region of the double layer. Furthermore aquantitative treatment is given of Frumkin's 107 suggestion that anions arepulled towards the metal as it acquires a positive charge.Several papers have been published on theoretical and experimentaltreatments of methods in which the current is interrupted, a matter of long-standing interest in the study of electrode processes.Grahame lo8 andScott log examined the problem theoretically; the treatment is limitedto electrodes without passivating layers. It was concluded lo* that infavourable cases the following parameters can be calculated; the I R drop,the capacity of the double layer, a lower limit to the product of the con-centration of the major reactant and its specific rate reaction constant, anda weighted average of the forward (+) and backward (ib) components of thecurrent : iav = aij + (1 - a)&.Scott log examined the interpretation of potential-time curves when thediffusion in one or both phases plays a major r61e. Publications by Fischer,Seipt, and Morlock lloU and particularly papers by Seipt and Gierst lloCconstitute a valuable examination and analysis of current interrupterexperimental methods.The Reporter thanks his colleagues for discussions, Dr.R. Parsons for kindlylending manuscripts of papers in the press, and Dr. Milica Liler who translateda number of the Russian papers referred to in the report.H. R. T.lo' A. N. Frumkin, Trans. Furuduy SOC., 1940, 36, 117.lo* D. C. Grahame, J . Phys. Ghem., 1953, 57, 257.lo9 W. T. Scott, J . Ckm. Phys., 1955, 23, 1936.110 (a) H. Fischer, M. Seipt, and G. Morlock, ref. 7a, p. 239; ( b ) M. Seipt, ref. 7b,p. 67; ( c ) L. Gierst, ref. 7b, p. 4930 GENERAL AND PHYSIC.4L CHEMISTRY.KINETICS OF CHEMICAL CHANGE.Kinetics in the Gas Phase.-The numerous publications in this field during1957 are considered under four headings-theoretical, techniques, inorganicsystems, and organic systems.Work on explosions and flames is notincluded.Theoretical. The Boltzmann equation has been considered from astatistical-mechanical point of view.l Chang has suggested a new methodfor determining the order and velocity constant of a reaction, and Flynnsuggests that many reactions in which the order changes during an experi-ment can be represented by &/dt = K ( l - x ) ~ . (1 - EX)”. He describeda method for calculating the constants I<, p, a, and V. The theory ofconsecutive reactions has been discussed,* and Monoszon has givenmathematical functions and relations that permit solution to give the rateconstants of the separate steps in a mixture of gases in which there are 3number of simultaneous reactions. Integrated rate equations for variousmechanisms by which three substances are interconverted by first-orderreactions have been derived as an interpretation of isotopic exchange in thepresence of an overall chemical reaction.6 The validity of the stationary-state approximation in the kinetics of chain reactions has been investigated.’Hirschfelder finds that it is accurate if the rates of destruction of theactive intermediates are rapid.Various Russian workers * have examinedthe theory of branched-chain reactions, especially the case of delayedbranching. Enikolopyan 8c has been able to explain why the rate of oxid-ation of some hydrocarbons is constant to a high percentage of reaction andalso why they end before all the reactants are used.Stepukhovich has calculated the activation energy of the decompositionof isopropyl, tert.-butyl, vinyl, and ally1 radicals, and has also investigatedthe effect of temperature on the steric factors of first- and second-orderreactions from the basic equations relating collision and transition-statetheories.He considers that this effect may be very important in free-radical reactions. The pre-exponential factors of hydrogen abstraction(e.g., CH,. + H,, CD,. + CH,) and reactions of chlorine atoms have beencalculated by means of the transition-state theory.l0, l1 The structureand mechanical properties of the activated complex for the former areassigned from a set of empirical rules from molecular structure andspectroscopy, and there was good agreement with experiment within thelimits of error involved.1°M.S. Green, J . Chem. Phys., 1956, 25, 830.2 W. Chang, J . Phys. Chem., 1957, 61, 819.3 J . H. Flynn, ibid., p. 110.4 M. Talat-Erben, J . Chem. Phys., 1957, 26, 75.A. M. Monoszon, Trudy Moslaov. Automobi1.-Dorozh. Inst. im. V . M . PIolotova,R. A. Albertyand W. G. Miller, J . Chem. Phys., 1957, 26, 1231.1956, No. 18, 227; Chem. Abs., 1957, 51, 5515.7 ( a ) J , 0. Hirschfelder, ibid., p. 271; ( b ) J. G. Giddings, ibid., p, 1210.8 ( a ) Yu. S. Sayasov and A. B. Vasil’eva, Zhur. $2. Khim., 1955, 29, 802; (b) N. S.Enikolopyan, ibid., 1956, 30, 769; (c) idem, Doklady Akad. Nauk S.S.S.R., 1957,112, 93.A. D. Stepukovich, Zhur. $2. Khim., 1956, 30, 2387; Doklndy Akad. NaukS.S.S.R., 1956, 107, 436.D.J . Wilson and H. S. Johnston, J . Anzer. Chem. SOC., 1957, 79, 29.11 K. S . Pitzer, ibid., p. 1804KINETICS OF CHEMICAL CHANGE. 31Long 1, has suggested that the value (9-2 kcal./mole) found by Majury andSteacie l3 for the activation energy of CH,. + H, _+ CH, + H* may below owing to the formation of methane from a methyl radical and ethane.The equilibrium constants for hydrogen abstraction by trideuteromethylfrom methane and methyl from tetradeuteromethane and [l*C]methaneat 300", 450", and 600" K have been calculated from spectroscopic data.14Combined with the velocity constants for the first two forward reactionsthey give the velocity constants for the back reactions. Trotman-Dickenson15 has plotted log k for the reaction of methyl radicals withhydrocarbons against log k for the analogous reactions of trifluoromethyl.Two straight lines, both of unit slope, are obtained.An analysis of thestructure of the =CEO group has been used as a basis for understanding theprimary process in the photolysis of saturated aldehydes and ketones,especially those containing propyl or larger groups,16 and Calvert l7concludes from a discussion of the decomposition of formyl (HCO*) andacetyl (CH,CO*) radicals that the activation energies are either about 27 and1s or 15 and 10 kcal./mole respectively.niIoseley and Robb 18 have developed a valuable methodfor determining the rate constants of free-radical reactions by following thenon-stationary state in simple photoinitiated gas reactions.They measurethe change in pressure due to adiabatic temperature changes by means of adiaphragm manometer of sensitivity mm. Hg and time delay responseless than sec. Using acetone they determined a value of k forXH,* __t C2H, in good agreement with that of earlier workers. A non-optical shock-tube technique for studying kinetics at high temperatures hasbeen developed at the Cornell Aeronautical Lab0rat0ry.l~ It is a single-pulse method, the gas being allowed to remain at reaction conditions for acontrolled time and then cooled very rapidly. Flash spectroscopy has beenused to detect free radicals in the wake of a shock wave.20 The range ofconcentration and wavelength over which a photochemical reaction can bestudied is increased if a mirror is used to reflect the transmitted light backinto the system.21 Jucker and Rideal 22 have described a simple and novelxenon lamp, and Callomon and Ramsey 23 a microsecond flash-photolysisapparatus. An exploding wire, emitting light rich in ultraviolet in<1 millisec., has been used as a line source in flash p h o t ~ l y s i s .~ ~ Theresults are very reproducible.Two spectrometers which give the mass-spectrum of a gas diffusingthrough a pin-hole from a reaction system 20 or 60 times per secondl 2 L. 11. Long, J . Phys. Chem., 1957, 61, 821.l3 T. G. Majury and E. \V. R. Steacie, Canad. J . C h e w , 1952, 30, 800.l4 F. S. Deinton, K. J. Ivin, and F. Wilkinson, Tyans. Faradny SOC., 1957, 53, 1204.l5 A. F. Trotman-Dickenson, Chewz.and Ind., 1957, 1243.l6 P. P. Manning, J . Amer. Chem. SOC., 1957, 79, 5151.l8 F. Moseley and J. C . Robb, Proc. Roy. SOC., 1957, A , 243, 119, 130.lY €1. S. Glick, J. J. Klein, and W. Squire, J . Chem. Phys., 1057, 27, 850.2 3 C. E. Cambell and I. Johnson, ibid., p. 316.21 J . A. Davies and P. P. Manning, J . Amer. Chem. SOC., 1957, 79, 5148.22 H. Juckerand (Sir) E. K. &deal, J., 1957, 1068.23 J . H. Callomon and D. A. Ramsey, Canad. J . Phys., 1957, 35, 120.24 G. K. Oster and R. A. Marcus, J . Chem. Phys., 1957, 27, 189.He favours the lower values.Techniqztes.J. G. Calvert, J . Phys. Chem., 1957, 61, 1206TABLE 1. A rrhenius parameters of homogeneous elementary reactionsReactionH,O, --t 2OHO*+O,+M+O,+M03+M.+O2+O.+M0. + 0, --t 202F, + IF5 + IF,2Br + A(0,) + Br, + A(OA21 + A ---+ I, + A2CIO* + C12 + 0 2CIO.+ CI,O ---t CIO, + CI,CIO- + CI,O --t CI + 0 2 + CI,N2+ 0.- NO + NN.+ NO--+, N,+ 0.No + NO + N, + 0.N. + 0, + NO + 0.NO + 0- --t NO,NO + O.+ M -+ NO, + MNO,+C + M - w N O , + MNO0 j- 0.- NO + 0 21\!32 + 0. --t NO 3- 0 2NO*+ 0*+NO + 0 2NO+O2+NO~+NOs+NO,NtOS + NO, + NO,NO2 + CO --t NO + COZMethod *SSI F J 1 F1)- Sh-l \ NJ ] PhNSISF ,A (or k or P )(c.c., moles, sec.)(4.61 & 0.25) x 10151013(2.96 -I: 0.21) x 1013(6.00 & 0.33) X 1013---k = (2.4 0.4) x lolok = l o s tP - 0.06k = 5.3 x 107k 2 4 x 10'1f-' k>1013-2 x 1012k = 1.8 x 10l6k = 1.0 x l O " tk = 2.1 x 1012k>1012 tk = 6-58 x lo7P N lo-'1013.1-14.11.2 x 1013* S, Static; T , thermal decomp.of 0,; F, flash photolysis; F,, flash photolysis ofshock tube reaction N, + 0, f- 2NO; N , flow reaction of N atoms a t low pressure:I, infrared spectrometry. t At room temperature. 8 At 25" CKINETICS OF CHEMICAL CHANGE. 33have been de~cribed.~~ Kistiakowsky and Kydd 25a state that with theirinstrument a component present at a mole fraction of 0.005 can be observedin a single spectrum with reasonable certainty. Hisatsune, Crawford, andOgg 26 have described a fast scanning infrared spectrometer.Reed and Rabinovitch 27 have used a spherical source, namely a hollowsteel sphere with 24 perforations uniformly placed, to study sodium flamereactions. This reduces the theoretical difficulty of calculating velocityconstants but the average value for the reaction of sodium with methylchloride is higher than that for nozzle flames.The transfer of energy is obviously important in gas-phase reactions, sowe may mention that Arnold, McCoubrey, and Ubbelohde 28 have calculatedthe probability for de-excitation of vibration in a collision from theexperimentally determined relaxation times for energy transfer betweenvibration and translation in various gases.Inorganic systems.Many of these systems have been investigated andthe kinetics of some elementary processes are given in Table 1.By investigating the effect of wall coating on the hydrogen-oxygenreaction Warren38 has been able to find the relative efficiencies of surfacestowards destruction of He, Om, *OH, H02*, and H202.The photolysis ofwater vapour at temperatures up to 270" c with light of wavelength about1650 A gives hydrogen, oxygen, and hydrogen peroxide in varying amountsdepending on the geometry of the ~ystern.~9 The decomposition of hydrogenperoxide below 20 mm. in static and flow systems in carefully cleaned glassreaction vessels becomes homogeneous above 400-450" ~ . ~ ~ 9 40 The actualkinetics are however not in complete agreement. Benson and Axworthy 30consider that at about 100" c the kinetics of the thermal decomposition ofozone in the presence of gases such as carbon dioxide, nitrogen, or heliumcan be explained without postulating an energy chain. The photolysis bylight of short wavelength appears to be a photon-propagated reaction.41In flash photolysis vibrationally excited oxygen molecules in the groundelectronic state are formed and possess sufficient energy to decompose ozone2 5 ( a ) G.B. IGstiakowsky and Y. H. Kydd, J . Amev. Chena. SOC., 1957, 79, 4826;26 I. C. Hisatsune, B. Crawford, and R. A. Ogg, J . Amer. Chew. SOC., 1957,2 7 J . F. Reed and B. S. Rabinovitch, J . Cheim. Phys., 1957, 27, 988.28 J. W. Arnold, J. C. McCoubrey, and A. R. Ubbelohde, Trans. Favaday SOC.,2 9 P. A. Gigukre and I. D. Liu, Canad. J . Chew., 1957, 35, 253.30 S. W. Benson and A. E. Axworthy, J . Chew. Phys., 1957, 26, 1718.32 J. Fischer and R. K. Steunenberg, J . A m e v . Chewz. SOC., 1957, 79, 1876.32 I<. L. Strong, J.C. W. Cltien, P. E. Graf, and J . E. Will~rd, J . Chena. Phys.,33 F. 11. C . Edgecornbe, I<. G. W. Xorrish, and B. A. 'I'hrusli, I'm-. Roy. Soc., 1957,( b ) L. B. Blanchard, J . B. Farmer, and C. Ouellet, Cmzad. J . Chem., 1957, 35, 115.79, 4648.1957, 53, 738.1957, 26, 1287..1, 243, 82.G. B. Kistiakowsky and G. G. Volpi, J . Chcm. Yhys., 1957, 27, 1141.:rs H. W. Ford and N. Endow, ibid., p. 1156.n o J . D. Ray and R. A. Ogg, ibid., 1057, 26, 984.L 7 H. S. Johnston, W. A. Bonner, and D. J. Wilson, ibid., p. 1002.3 8 D. R. IVarren, ?'vans. Faraday SOC., 1957, 53, 199.M. C. Clien and H. A. Taylor, J . Chem. Phys., 1957, 27, 857.4 0 C. N. Satterfield and T. W. Stein, J . Phys. Chern., 1957, 61, 537.41 S. W. Benson, J . Chern. Phys., 1957, 26, 1351.REP.-VOI,.LIV 34 GENERAL AND PHYSICAL CHEMISTRY.molecules to give chains involving atoms and energised andMcGrath and Norrish question the mechanism for the thermal decom-position suggested by Benson and A x ~ o r t h y . ~ ~The rate of dissociation of bromine in the presence of argon, and thevisible emission from hot, partly dissociated bromine produced by a shockwave, have been studied at 1200-2500" K . ~ ~ , ~ ~ The activation energy ofthe reaction is approximately equal to the dissociation energy of bromine,and from the frequency factors it appears that both vibration and rotationof the molecule contribute to the diss~ciation.~~ The continuous emissionis caused by the re-formation of bromine molecules in various excitedstates.& The velocity constants for the third-order recombination of iodineatoms up to 160" c determined by flash photolysis agree with earliervalues3, The reaction of hydrogen with bromine at 850-1140" K in ashock tube above the explosion limit has been in~estigated.~~ The low-temperature reaction scheme with extrapolated values of the individualreaction constants (Table 1) explains the results.Much work has been reported on systems involving nitrogen compounds.The spontaneous ignition and luminescent decomposition of hydrazoic acid,HN,, have been studied.4G Bell, Robinson, and Tren~ith,~' who haveinvestigated the decomposition of nitrous oxide in the presence of carbondioxide, sulphur hexafluoride, and inert gases at 650-750", consider that itfollows activation by two processes: (1) 2N20 _t.N20* + N,O and(2) N20 + X - N,O* + X, E , - El being ca. 3 kcal./mole. There hasbeen some discussion on the rBle of nitrogen trioxide, NO,, in thedecomposition of the dioxide.48 The effect of foreign gases on thedecomposition of dinitrogen pentoxide in the presence of excess of nitricoxide within a limited pressure range is in general conformity withLindemann's the0ry.~9 The kinetics of the reaction of nitric oxide withhydrogen at 850-1060" c indicate that a chain mechanism operates.50 Thereaction of nitrogen dioxide with hydrogen at around 400" c has beenstudied by Ashmore and Levitt 51 and by Rosser and Wise.52 The kineticresults and the free-radical chain suggested by both pairs of workers agree,the overall activation energy determined being nearly the same, 43 and46 kcal./mole respectively.The oxidation of ammonia by nitrogen dioxideat 327-527" c in a static system has been followed by measuring the changein optical density of the latter.53 The reaction was of the second orderwith an overall activation energy of 27.5 kcal./mole. The effect of carbon42 W. D. McGrath and R. G. W. Norrish, Pvoc. Roy. SOC., 1957, A, 242, 265; Nature,43 H. B. Palmer and D. F. Hornig, J . Chem. Phys., 1957, 26, 98.44 H. B. Palmer, ibid., p. 648.4 5 M. N. Plooster and D. Garvin, J . Amer. Chem. SOC., 1956, 78, 6003.4 6 P. Gray and T. C. Waddington, Nature, 1957, 179, 576.4 7 T. N. Bell, P. L. Robinson, and A. B. Trenwith, J., 1957, 1474.48 N.Davidson and G. L. Schott, J . Chem. Phys., 1957, 27, 317; Y. G. 14shmore49 J. Jack, Trans. Faraday Soc., 1957, 53, 41.5 0 W. M. Graven, J . Amer. Chem. SOC., 1957, 79, 3697.5 1 P. G. Ashmore and B. P. Levitt, Trans. Furaduy SOC., 1957, 53, 945.52 W. A. Rosser and H. Wise, J . Chew. Phys., 1957, 26, 571.53 Idem, ibid., 1956, 25, 1078.1957, 180, 1272.and B. P. Levitt, ibid., p. 318KINETICS OF CHEMICAL CHANGE. 35mass (12C and 13C) on the rate of oxidation of carbon monoxide by nitrogendioxide decreases slightly with temperature; k12/k13 = 1.022, 1.019, and1.016 at 267", 365", and 454" c re~pectively.~~have investigated the combustion of hydrogensulphide by flash photolysis and kinetic spectroscopy. If little inert gasis present sulphur dioxide is formed by steps involving *SH and *OH, butwith a large excess or at a low temperature mainly disulphur dioxide, S202,is obtained. The photodecomposition of carbon dioxide by 1470A xenonradiation to give carbon monoxide does not involve atomic oxygen.22 Theeffect of phosphine on the ignition limits of mixtures of carbon monoxideand oxygen has been studied.55 If the rate of association of BH, radicals iscomparable with that of CH, radicals, then the results from eight studies ofkinetics of reactions of diborane lead to compatible upper limits for the heatof dissociation of diborane, B2H,.56 Hydrogen and tetraborane are themajor products of the mercury-photosensitised decomposition of diboranea t 2 9 .3 " c . ~ ' The primary step is probably B2H, + Hg* B2H, +He + Hg.A preliminary investigation of the photolysis of pentaboranevapour has been reported.58Organic systems. The few systems which appear to involve simple uni-or bi-molecular reactions are discussed first. Weston 59 has studied thetritium isotope effect in the isomerisation of cyclopropane. At 406-4 9 2 " c/200 mm. the ratio of the velocity constants of the unlabelled to thatof singly-labelled species is 0.86 -& 0.06 exp (-385 -& 95/RT), and as thepressure is decreased the effect is reduced. The relation of the results toSlater's calculations 6o is discussed. The pyrolysis of ethylcyclobutane,giving ethylene and but-l-ene, and the elimination of formic acid fromtek-butyl formate are unimolecular processes, k being 3.6 x 1015 exp(-62,00O/RT) and 10ll.l exp (-36,40O/RT) sec.-l respectively.619 e2 Themercury-photosensitised decomposition of ethylene to acetylene andhydrogen appears to involve the primary formation of a triplet C2H,molecule, which isomerises to a molecule of uncertain lifetime in whichtwo hydrogen atoms act as bridges between the carbon atoms.63 Hydrogenis formed from these two hydrogen atoms.The kinetics of the pyrolysis ofNorrish and ZeelenbergH ,C-C H,-N+O\ ///nitroethane below 440" c in a flow or a static system fit the equation k =1010.8 exp ( - 3 9 , 7 0 O / R T ) sec. and Wilde 64 considers that the main processinvolves a direct splitting-off of nitrous acid, the activated complex having54 R. G. W. Norrish and A. P.Zeelenberg, Proc. Roy. SOC., 1957, A , 240, 293.5 5 F. I. Dubovitshii and M. F. Kuz'mina, Zhur. $2. Khirn., 1956, 30, 83756 S H Bauer, J Amer. Chern. SOC., 1956, 78, 5175.57 T. Hirata and H. E. Gunning, J . Chern. Phys., 1957, 27, 477.68 H. B. Burwasser and R. N. Pease, J . Phys. Chem., 1956, 60, 1589.59 R. E. Weston, J . Chern. Phys., 1957, 26, 975.6 0 N. B. Slater, Proc. Roy. Soc., 1953, A , 218, 224.61 R. E. Wellman and W. D. Walters, J . Arner. Chern. SOC., 1957, 79, 1542.6 2 E. Gordon, S. J. W. Price, and A. F. Trotman-Dickenson, J . , 1957, 2813.63 E. Whalley, Canad. J . Chem?., 1957, 35, 565.6j K. A. Wilde, J . Ph;>ls. Chew., 1957, 01, 385TABLE 2.Reaction MethodCH,* ---t CH,: + H*CH,: + H, ---t CH,(CH3)4C + CH3* + C4He Pyrolysis of neopentaneCH3. + CH,.CO*OCH, --t CH4 + .CH,*CO.OCH,A rrhenius parameters of free-radical reactions involving organic compounds.CD3* + C3H6 + CD3H + C3H5* Photolysis of (CD3),C0 + cyclicCH,.+ (CH3*CO)20 + CH, + CH,*C0.0*OC*CH2. Photolysis of (CH,-CO),OCH3. + CH,.CONH, --+ CHI + *CH,.CONH,CH,* + RSH --f CHI + RS* (R = Me, Et, Pr', But)} Pyrolysis of CH, and effect of addedCD3* + C,H,, --t CD,H + CSHg. } carbonsPhotolysis of CH,.CO*OCH,Photolysis of (CH,),CO + CH3CONH2Photolysis of (CH,),CO + thiolsCH3. + (CF,),CO --t CF,* + CH,.CO*CF,CH,. + C2HS + C3Hh.Pyrolysis of (CH3)2N2 + (CF,),COPyrolysis of [(CH,),CO], + olefinsPhotolysis of (C2H5),C0 by sector methodIlg-photodecomp. of H, + C2H,CH3* + C2H4 + C,H,*CH,. + C,H, ---t C4H,*CH3.+ CH,=CH*CH=CH2 + C,Hg.2C,H5* + C4H,,CgH5* 3- CIH4 + CIH,.CF3. + CHd + CF3H + CH3*CF3* + (CHJSCH --.) CF3H + (CH3)3C*CF,* + CH,*CHO --t CF,H + CH,*CO*Photolysis of CF,CHO + additives t JCH,O* + CH,C0.0CH3 -% CH,*OH + *CH,*CO.OCH, Photolysis of CH,.CO.OCH,CH,S* + CH,.CHO --t CH,*SH + CH,.CO* Photolysis of CH,.CHO + CH,SHC,H,.CO. + C,H,* + CO Photo-oxidation of (C,H5) ,CO2C,C14H* + inertPyrolysis of Zn(CH,), + C,H5*CH3,CI. + CH,CI*O.COCI + HCI + *CHCI-OCOCINa- + CH,CI --+ NaCl + CH,.Na. + CFH,CI + NaCl + CFH2*Na. + CF,HCI -+ NaCl + CF,H*Na. + CF,CI + NaCl + CF,.(CH,),CO*OC(CH,), + 2(CH,),CO*Zn(CHJ2 + ZnCH,. + CH,.ZnCH,* + Zn + CH,.(a) Pyrolysis of Cd(CH,), + C,H,-flow Cd(CHJZ --.) CdCH,. + CH,*( b ) Pyrolysis of Cd (CH,) 2, staticCdCH,* + Cd* + CHS*Photochlorination of C,C13H by thesector methodPhotochlorination of CH,Cl.O*COCl I Cl2 + C2CI,H* ---+c C2CIsH + CISNa flame} Pyrolysis of [CH,),CO], + NOI(CHJ3CO.--t (CHJ2CO + CH,.Hg(CHJ2 + HgCHs* + CH3* } Pyrolysis Hg(CH,), + C,H,CH,,{HgCH,* + Hg. + CH,.* C y c l i c s y s t e m s a r e s h o w n i n i t a l i c KINETICS OF CHEMICAL CHANGE. 37a ring structure (I). Dean and Marcus G5 have measured the relative ratesof the rapid bimolecular association between amines and boron trifluorideby means of a steady-state flow apparatus.New or revised values of the kinetics of various free-radical reactionshave been determined during the last year. These are summarised inTable 2.It will be realised that the values in Table 2 depend on the correctidentification of the elementary reactions taking place in the systems studiedand often on the assumption of values of the Arrhenius factors for otherreactions, e.g., 2CH3- C2H6, but for details the original papers should beconsulted.However, further discussion of some of the work listed aboveis desirable.Engel, Combe, Letort, and Niclause g7 investigated the pyrolysis ofpropane and pt- and iso-butane as well as of Pteopentane in the absence of eventraces of oxygen. The activation energy of hydrogen abstraction bytrideuteromethyl from cyclopropane is much larger than previouslyreported.68 At 375" c in McNesby and Gordon's system 68 cyclopropylradicals isomerise to prop-2-enyl, which do not abstract hydrogen readilybelow 500" c.57 In the photolysis of acetic anhydride Ausloos 70 found thatthere appeared to be an equal probability of an initial split to give acetoxyland acetyl radicals and a unimolecular decomposition giving formaldehydeand acetic acid.The yields of carbon monoxide and dioxide from thephotolysis of propionic anhydride showed that both propionyl and propionyl-oxyl decompose readily. The photolysis of acetamide alone was alsoinvestigated. 71 The primary step was either CH,*CO*NH2 __t CH,* +CO-NH, or CH3*CN + H20. The velocity constant for the reaction of themethyl radical with thiols increases as the hydrocarbon radical increases insize.72 Dodd and Smith 77 found that the dimerisation of trifluoromethyl rad-icals from the photolysis of trifluoroacetaldehyde was independent of pressuredown to 0.5 mm.The catalytic effect of thiols on the photodecompositionof acetaldehyde increased in the order H2S > MeSH > EtSH > PriSH >B u ~ S H . ~ ~ In the photo-oxidation of acetone the yield of carbon monoxideis very small at high oxygen pressures, indicating that none is formed byreaction of propionyl with oxygen.79 The collision yield for the reactionC2H5* + 02- C,H50,* was calculated to be It is suggested,however, that the ethylperoxy-radical, C2H502, does not form acetaldehydeplus hydroxyl or ethyl hydroperoxide under these conditions. The chains6 5 J. Dean and R. A. Marcus, J . Chem. Phys., 1957, 26, 162.6 6 P. S. Shaiitarovich and B. V. Pavlov, Zhur.fiz. Khim., 1956, 50, 811.b7 J. Engel, A. Combe, M. Letort, and M. Niclause, Compt. rend., 1957, 244, 453.68 J. R. McNesby and A. S. Gordon, J . Amer. Chem. SOL, 1957, 79, 825.69 M. H. J. Wijnen, J . Chem. Plzys., 1957, 27, 710.70 P. Ausloos, Canad. J . Chem., 1956, 34, 1709.71 B. C. Spa11 and E. W. B. Steacie, Proc. Roy. SOL, 1957, A, 239, 1.72 J . A. Kerr and A. F. Trotman-Dickenson, J., 1957, 3322.73 G. 0. Pritchard and E. W. R. Steacie, Canad. J . Chem., 1957, 35, 1216.74 L. C. Landers and D. H. Volman, J . Amer. Chem. Soc., 1957, 79, 2996.75 A. Shepp and K. 0. Kutschke, J . Chem. Phys., 1957, 26, 1020.76 J. A. Pinder and D. J. LeRoy, Canad. J . Chern., 1957, 35, 588.77 R. E. Dodd and J. W. Smith, J., 1957, 1465.7 8 R. N. Birrell, R.F. Smith, A. F. Trotman-Dickenson, and H. Wilkie, ibid., p. 2807.7@ J. E. Jolley, J . Amer. Chem. SOC., 1957, 79, 153738 GENERAL AND PHYSICAL CHEMISTRY.in the photochlorination of chloromethyl chloroformate apparentlyterminate by a first- or a second-order process.81 The results of Belgianworkers on the photochlorination of chloroform and chloroethylenes havebeen summarised.88 They have developed a general reaction scheme andbeen able to derive much quantitative kinetic data on various elementaryprocesses involving chlorine atoms and chlorine-containing radicals, whichare too extensive to include in Table 2. From the effect of nitric oxide onthe decomposition of tert.-butyl peroxide Birss, Danby, and Hinshelwood 83calculate that the steric factor for the association of methyl with nitric oxideis about 7 x lo5 times less than that for the association of two methylradicals to form ethane.Much work has been published on organic systems in which no quantit-ative kinetics of individual steps has been deduced.The pyrolysis ofmethane at 1000" c in a silica tube is a homogeneous first-order reacti0n.8~Parsons, Danby, and Hinshelwood consider that ethane may decomposein two ways: (1) C2H6 + C,H, + H, or (2) C2H6 __t CH, + CH,, theCH,: radicals giving the other products. The rate of reaction (1) is reducedto a limit by the addition of nitric oxide, and the effect of sulphur hexa-fluoride on the forward and back reactions leaves the equilibrium constantunchanged. The decomposition is initiated at 368" c by azomethaneMe,N,,Q1 and the reaction of oxygen atoms, from the photolysis of nitrousoxide, with ethane is more rapid than with nitrous oxide it~elf.9~ At highpressures, 400-2000 atm., the rate of polymerisation of ethylene dependson high powers of the pressure, but if fugacities are used the kineticexpressions are compatible with the usual free-radical chain mechanism.93The polymerisation of acetylene below 550" c in a static system is reportedto give reproducible second-order velocity constants, the overall activationenergy being 46.7 & 2 k~al./mole.~~ Silcocks 95 has also studied the thermalreactions at 352-472"~ in a static system.He finds that homogeneoussecond-order polymerisation occurs, k = 3-72 x 1013 exp (-60,20O/RT)cm.3 mole-1 sec.-l, combined with a surface reaction.The mercury-photosensitised decomposition of allene and buta-1 : 2- and -1 : 3-diene,968 0 F. S. Dainton, D. A. Lomax, and M. Weston, Trans. Faraday SOC., 1957, 53, 460.81 M. J. Dignam, W. G. Forbes, and D. J. LeRoy, Canad. J . Chem., 1957, 35, 1341.82 J. F. Reed and B. S. Rabinovitch, J . Phys. Chem., 1957, 61, 598.83 F. W. Birss, C. J. Danby, and (Sir) C. Hinshelwood, Proc. Roy. SOC., 1957, A ,84 S. J. W. Price and A. F. Trotman-Dickenson, Trans. Faraday SOC., 1957,53, 1208.86 Idem, ibid., p. 939.86 C. M. Laurie and L. H. Long, ibid., p. 1431.8 7 J. R. McNesby and A. S. Gordon, J . Amer. Chem. SOC., 1957, 79, 4593.88 M. Ackermann, G. Chiltz, S. Dusoleil, P. Goldfinger, G.Martens, and D. Vander Auwera, Nature, 1957, 179, 731 : G. Chiltz, G. Martens, and A. M. Mahieu, Nature,1957, 180, 1068.89 J. E. Germain and C. Vaniscotte, Bull. SOC. chim. France, 1957, 692.9 0 B. N. Parsons, C. J. Danby, and (Sir) C. Hinshelwood, Proc. Roy. SOC., 1957,91 A. D. Stepukhovich and E. G. Kaplan, Zhur. $2. Khim., 1956, 30, 928.99 G. A. Castellion and W. A. Noyes, J . Amer. Chem. SOC., 1957, 79, 290.93 R. K. Laird, A. G. Morrell, and L. Seed, Discuss. Faraday SOC., 1957, 22. 126.94 G. J. Minkoff, D. M. Newitt, and P. Rutledge, J . Appl. Chem., 1957, '9, 406.95 C. G. Silcocks, Proc. ROY. SOC., 1957, A, 242, 411.96 J. Collin and F. P. Lossing, Canad. J. Chem., 1957, 35, 778.239, 154.A , 240, 333KINETICS OF CHEMICAL CHANGE. 39and the thermal decomposition of isobutene 97 have been investigated.Allenegives C,H,* radicals (probably *CH,--C- CH). The light emission from di-acetylene at 0.5min. subjected to flash photolysis shows C,, C,, and CH bands.23Atkinson and Atkinson 98 studied the kinetics and products of thepyrolysis of systems derived from tetrafluoroethylene at 550-750" c , andTrenwith and Watson 99 that of three chlorofluoromethanes at 400-900" c.Free radicals such as CF,:, CF,., and CF,Cl- have been suggested as inter-mediates. The activation energies of the thermal decomposition ofchloroform and deuterochloroform are identical: 37-2 & 2 and37.5 & 2 kcal./mole respectively.loO An upper limit to the value ofD(CHCl,-Cl) of 72 kcal./mole has been calculated.The reaction of ethylbromide to give ethylene and hydrogen bromide, although of the first orderat 310476" c, is complex.lol The primary step is probably unimolecularwith an activation energy about 52 kcal./mole, followed by a surface reactionof the hydrogen bromide and ethyl bromide giving bromine atoms. Thephotolysis in excess of cyclopentane gives ethane as the main product, inwhich the 12C enrichment was 1.0070 & O-OO08.102 Holmes and Maccoll lo3have reinvestigated the pyrolysis of isopropyl iodide. Above 285" c thereappears to be a unimolecular elimination of hydrogen iodide followed bya rapid reduction of the isopropyl iodide by hydrogen iodide, and below thattemperature a further autocatalysis by the iodine molecules formed.The pyrolysis of rt-butanol at 573-629" c is of the first order,lW k =1012.2 exp (56,70O/RT) sec.-l.The primary step probably gives wpropyland hydroxymethyl radicals. The ratio of ethane to carbon monoxide(ca. 1.25) in the products of the high-intensity flash photolysis of acetonevaries little with the pressure.lo5 There is some evidence for the formationof long-lived excited acetone molecules below 210 mp. Lossing106 hasfollowed the mercury-photosensitised decomposition of acetone andacetaldehyde at room temperature by means of a mass-spectrometer. Theprimary steps are Hg* + (CH,)&O -+ Hg + CH,. + CH,*CO*and Hg* +CH,*CHO _+ Hg + CH,. + CHO., and at least 25% of the acetyl radicalsare sufficiently long-lived to react with another hot mercury radical, Hg*.The effects of carbon dioxide and oxygen on the photolysis of acetone showthat the reactions (1) CH,*CO* + M --+ CH,* + CO + M and (2) CH,.+0, + M - CH3*02 + M occur.1o7 If M is acetone then at 200" c k , =1.6 x 10-31 cm.6 molecule-2 sec.-2. The results of the photolysis of hexa-deuteroacetone in the presence of four butenes show that trideuteromethyl9 7 Yu. I. Liadova, V. I. Vedeneyev, V. V. Voewdsky, Doklady Akad. Nauk, S.S.S.R.,98 B. Atkinson and V. A. Atkinson, J., 1957, 2086.D9 A. B. Trenwith and R. H. Watson, ibid., p. 2368.1957, 114, 1269.100 G. P. Semeluk and R. B. Bernstein, J. Amer. Chem. Soc., 1957, 79, 46.101 A. E. Goldberg and F. Daniels, ibid., p. 1314.102 H. L. Friedman, R. B. Bernstein, and H. E. Gunning, J.Chem. Phys., 1957,103 J . L. Holmes and A. Maccoll, Proc. Chem. Soc., 1957, 175.lo4 J . A. Barnard, Trans. Faruday Soc., 1957, 53, 1423.105 G. K. Oster and R. A. Marcus, J. Chem. Phys., 1957, 27, 472.106 F. P. Lossing, Caxad. J. Chem., 1957, 35, 305.107 D. E. Hoare, Trans. Faruduy Soc., 1957, 53, 791; D. E. Hoare and A. D. Walsh,26, 528.ibid., p. 110240 GENERAL -4ND PHYSICAL CHEMISTRY.radicals may add to each carbon atom of the double bond, the radicalformed often losing a methyl radical, or may abstract an a-hydrogen atom.losThe photolysis of the three branched-chain dibutyl ketones enables the ratioof the rates of disproportionation (1) to dimerisation (2) of butyl radicalsto be determined: KJk, = 4-59 (tert.), 0.418 (iso), and 2.27 (sec.).If the values of k , are equal then the factor determining k , is the number ofavailable hydrogen atoms which can be removed to give a stable olefin.Thepyrolysis of n-butyl methyl ketone at 430-500" c is predominatelyhomogeneous, the apparent activation energy being 52 & 3 kcal./mole.l1°The reaction involves the CH,*CO*C,H,* radical which may decompose invarious ways. The products cf the photolysis of cyclobutanone, cyclo-pentanone, and cyclohexanone at 100--300" c suggest that the initial stepis a split at either the CH2-CO bond or a CH2-CH, bond.ulThe photolysis of keten and mcthyl- and dimethyl-keten under variousconditions has been studied extensively, especially with regard to thereactions of the radicals, e.g., CH,:, p r o d u ~ e d .~ ~ ~ , l l ~ The results at -78"and of the flash photolysis indicate that the reaction of methylenewith keten is very 25a Added oxygen mainly deactivatesexcited keten (CH,:CO) molecules at room temperature.l12c Kistiakowskyand Mahan 112d suggest that vibrationally excited ethylidene radicalsCH,*CH: are produced from methylketen and rearrange at measurable ratesinto ethylene. Propene and carbon monoxide are the major productsfrom dimethylketen, probably via (CH,),C=C=O __t CO + (CH,),C: +C3HB.112e Methylene radicals appear to react with paraffins to give onlythe next higher member of the series.l12f With ethylene and propene orcyclopropane a t very low pressures, mainly propene and butanes respectivelyare fonned.112g~h As the pressure is increased the yield of cyclopropane andmethylcyclopropane respectively increases.The energy-rich moleculesfornied by addition of methylene either deactivate on collision orisomerise, e.g.,MCH2 + C,H,--t CH,-CH2* - + CH,-CH, CH,CH-CH* 'd (11) '\ / ';< h 2 = C H . C H , CH,Okabe and Noyes113 describe a technique for measuring the relativeintensities of the blue fluorescence and green phosphorescence of diacetyl,(MeCO),. The ratio green : blue at 26" c/42 mm. is 58 8. It decreasesas the temperature is raised, and falls rapidly to zero as oxygen is added.Cvetanovic and Doyle 114 have studied the mercury-photosensitisedlo8 J. R. McNesby and A. S. Gordon, J . Amev. Chem. SOC., 1957, 79, 5902.lo9 J. W. Kraus and J. G. Calvert, ibid., p.5921.111 F. E. Blacet and A. Miller, ibid., p. 4327.112 ( a ) G. B. Porter, ibid., p. 827; ( b ) W. G. Paterson and H. Gesser, Canad. J .Chem., 1957, 35, 1137; (G) G. B. Porter, J . Amer. Chem. SOL, 1957, 79, 1878; ( d )G. B. Kistiakowsky and B. H. Mahan, ibid., p. 2412; (e) R. A. Holroyd and F. E.Biacet, ibid., p. 4830; (f) J. H. Knox and A. F. Trotman-Dickenson, Chem. and Ind.,1957, 731; (g) H. M. Frey, J . Amer. Chem. SOL, 1957, 79, 1259; ( h ) J. H. Knox andA. F. Trotman-Dickenson, Chem and Ind., 1957, 1039.113 H. Okabe and W. A. Noyes, J . Amer. Chem. Scc., 1957, 79, 801.114 R. J. Cvetanovic and L. C. Doyle, Caszad. J . Chesn., 1957, 35, 605.W. T. Barry and W. D. Walters, ibid., p. 2102KINETICS OF CHEMICAL CHANGE. 41decomposition of 2 : 3-epoxybutane at 25" c.They suggest that methyl andepoxypropyl (11) radicals are formed in the primary step. The kinetics andproducts of the reaction of acetaldehyde with nitrogen dioxide at 110-180" have been in~estigated.11~ A mechanism is suggested involving acetyland methyl radicals. The decompositions of propyl nitrite and butyl nitritein a static system are of the first order, the overall activation energies being34-7 and 26.2 kcal./mole respectively.l16In conclusion some work on gas-phase oxidation systems will be brieflymentioned. An extensive investigation of the slow combustion of methaneat 460-520" c has been reported by Egerton, Minkoff, and Sa10oja.l~~Considerable quantities of hydrogen peroxide are formed as one inter-mediate (the other being formaldehyde), provided that the surface of thevessel has been treated with acid.It appears to undergo a homogeneoussplit leading to branching (see ref. 29). The oxidation of n-heptane in aflow system a t 300" c gives a mixture of aldehydes, and the products from[l-2H]propane and [2-2H]propane with a small amount of oxygen show thatat 360420" c the attack at a secondary carbon-hydrogen bond is 1.9 timesfaster than attack at a primary one.118 The slow combustion of methanoland ethanol has been studied.ll9 Delayed branching is due to formaldehydeand acetaldehyde with the former and the latter respectively. The effect ofethane on the first limit of the hydrogen-oxygen reaction at 540" c invessels coated with potassium chloride suggests that hydrogen atoms arereplaced by HO,.radicals by the steps H* + C2H, _t H, + C2H5* andC2H5* j- 0, _t C2H, + H0,*.120 The rate of formation of acetic acid inthe oxidation of ethane catalysed by hydrogen bromide increases withincrease in hydrogen bromide concentration but does not depend on theethane or oxygen concentrations.121 The kinetics of the mercury-photo-sensitised oxidation of ethane show that the formation of ethylhydroperoxide, the primary product, is probably not a free-radical chainreaction .lZ2haspublished an important series of papers on the theory of electron-transferreactions. In the first is presented a method of calculating the free energyof reorganisation of the solvent molecules around the reactants before theelectronic jump, and from this is developed a quantitative theory of electron-transfer reactions. In such reactions only a slight overlap of the electronicReactions in Solution.-During the past year, R.A. Marcus 1s 2 s115 A. E. Pedlar and F. H. Pollard, Trans. Faraday Soc., 1957, 53, 44.116 M. F. Nagiev, 2. G. Petrova, and A. I. Sultanova, Doklady Akad. Nauk, S.S.S.R.,117 (Sir) A. Egerton, G. J. Minkoff, and K. C. Salooja, Proc. Roy. Soc., 1956, A ,118 R. Burt, F. B. Ebeid, and G. J. Minkoff, Nature, 1957, 180, 188.119 K. M. Bell and C. F. H. Tipper, Yroc. Boy. Soc., 1956, A , 238, 256; Trans.Faraday Soc., 1957, 53, 892; C. F. Cullis and E. J. Newitt, Proc. Roy. Soc., 1956, A ,237, 530; 1957, A , 242, 516.l20 R. R. Baldwin and R. F.Simmons, Trans. Favaduy Soc., 1957, 55, 955, 964.121 M. F. Sedova and N. M. Emanuel, Izvest. Akad. Nauk, S.S.S.R., Otdel Khitn.122 J. S . Watson and B. de B. Danvent, J . Phys. Chem., 1957, 61, 577.1956, 109, 573.235. 158; Combustion and Flame, 1957, 1, 25.N a u k , 1956, 658.R. A. Marcus, J . Chem. Phys., 1956, 24, 966.2 Idem, ibid., 1957, 26, 867.3 Idem, ibid., p. 87242 GENERAL AND PHYSICAL CHEMISTRY.orbitals of the reacting molecules is to be expected. In most reactionsthere is usually a transfer of atoms or groups of atoms between the reactantsand one would expect a considerable spatial overlap of the electronic orbitalsof the reacting molecules in the transition complex. The assumption ofslight overlap is shown to lead to a reaction path which involves an inter-mediate state X * in which the electrical polarisation of the solvent doesnot have an equilibrium value.This state X * can either re-form thereactants or, by electron transfer, form a state X in which the ions arecharacteristic of the products. Free energies and entropies of activationof some inorganic electron-exchange reactioiis have been calculated fromthe theory without the use of adjustable parameters. It is suggested thatreactions like that of ferrous ion with FeC12+, which probably has an atom-transfer mechanism, should be studied in deuterium oxide because theabsence of an isotope effect would be expected if chlorine-atom transferoccurs (unless the O-H vibration frequencies in the hydration shells changeappreciably when the activated complex forms).Free energies and entropiesof activation have been calculated for some organic redox reactions.It has been shown that the application of differential thermal analysisto reaction kinetics can provide the frequency factor, the activation energy,and the heat of reaction from a single rapid measurement.* A generalequation has been derived for the kinetics of complex isotopic exchangereactions in which each of three non-equivalent species is exchanging withthe otherThese formpart of an extensive review by Stranks and Wilkirx6 Hudis and Dodson 7have concluded that the isotopic exchange between iron@) and iron(m) isbrought about by hydrogen-atom transfer since the reaction rate is reducedwhen deuterium is substituted for hydrogen.These findings have beenconfirmed by a recent study of the neptunium(v)-neptunium(v1) exchangein both water and deuterium oxide.8 It was also demonstrated thatthe rate is unaffected by substitution for sodium by magnesium or lanthanumperchlorates, even at ionic strengths as high as 3M.Interest has increased in the effect of anions on mechanisms of inorganicreactions as illustrated by the investigations of Brubaker and his co-workerson the thallium(1)-thallium(m) reaction.g* lo In 2-19~-sulphuric acidexchange is about 200 times as fast as in perchlorate solutions of the sameacidity and ionic strength, the mechanism beingElectron-exchange reactions between ions of the same metal.*TIsf + TISO,- __t TI3+ + *TISO,-*TISO,+ + TI(SO,J,S- __t TISO$ + *TI(S0,J23-*TI(SO&- + TISO,- d TI(SO,J,- + *TISO,-Steps having reactants with opposite charges were preferred but it isnow becoming apparent that coulombic forces are not necessarily significant4 H.J . Borchardt and F. Daniels, J. Amer. Chem. SOC., 1957, 79, 41.6 D. F. Abell, N. A. Bonner, and W. Goishi, J . Chem. Phys., 1957, 27, 658.6 D. R. Stranks and R. G. Wilkins, Chem. Rev., 1957, 57, 743.7 J. Hudis and R. W. Dodson, J. Amer. Chem. Soc., 1956, 78, 911.8 J. C. Sullivan, D. Cohen, and J . C. Hindman, ibid., 1957, 79, 3672. * C. H. Brubaker and J . P. Mickel, J. Inorg. Nuclear Chem., 1957, 4, 55.10 C. H. Brubaker, K. 0. Groves, J. P. Mickel, and C. P. Knop, J. Amer. Chem. Soc.,1957, 79, 4641KINETICS O F CHEMICAL CHANGE.43in such reactions. The addition of chloride ions to the system causes therate to pass through a minimum (as was found earlier by Harbottle andDodson 11 who used perchlorate media) : the initial decrease was attributedto the failure of T1Cl2+ and TlCl,+ to exchange appreciably with thallium(1)whereas the increase at higher [Cl-] : TlIII ratios is believed to be due torapid exchange between TlC1,- and thallium@) chloride complexes. It isnoteworthy that the most rapid exchange occurs when both the valencystates of thallium are carrying the same sign of charge. The effect ofanions on another well-established exchange reaction has been studied,namely the influence of thiocyanate on the exchange between ferrous andferric iron.12 Four reaction paths appear to be available, i.e., Fe2+ canexchange with FeSCN2+, Fe(SCN),+, Fe3+, or FeOH2+; these paths andthe energies associated with them are similar to those found for the additionof chloride13 or fluoride14 ions.In perchlorate media at an ionic strength of 2 .0 ~ the isotopic exchangebetween plutonium(II1) and plutonium(1v) was l5 100 to 1000 times as fastas the ferrous-ferric reaction so that concentrations in the range l O - 5 ~ to10-GM had to be used. The two reaction paths Pu3+ + Pu4+ and PIP+ +PuOH3+ accounted for the kinetics.Sulphate complexes dominate the mechanisms of both the forward andthe reverse reaction of the equilibrium NplV + NpVI =F+ 2NpV whichhas been investigated in sulphate media.16The cerium(In)-cerium(Iv) reaction in 6.0~-perchlorate has been found tobe of the second order in cerium(Iv), the dependence on hydrogen ion concen-tration being complex; exchange between CeIII and the species Ce(OH),2+,Ce(OH),+, and CeOCeOH5+ accounts for these facts.17The exchange of 54Mn between MnO,,- and Mn0,- in O.lG~-sodiumhydroxide has a specific rate constant of 710 1.mole-l sec.-l at 0"c and anoverall activation energy of 10.5 kcal. mole-l.18The rate of the neptunium(v)-neptunium(v1) exchange in perchloricacid is not affected by the variation of the macroscopic dielectric constantbrought about by the addition of ethylene glycol or sucrose.19 It appearsthat non-electrostatic forces dominate the energetics, i.e., the exchangemay proceed by transfer of an atom.Many systems have been studied having water as solvent and nowattention is being turned to other solvents; an example is the exchangereaction between stannic and stannous chlorides in pure methanol.20Magnetic resonance holds out a meansof determining rates of very fast reactions in this class.One of the firstto be studied is the electron exchange between neutral molecules andOther electron-exchange reactions.l 1 G. Harbottle and R. W. Dodson, J . Amer. Chem. SOC., 1951, 73, 2442.1% G. S. Laurence, Trans. Faraday SOC., 1957, 53, 1326.I 3 J. Silverman and R. W. Dodson, J . Phys. Chem., 1952, 56, 846.14 J. Hudis and A. C. Wahl, J . Amer. Ckem. SOC., 1953, 75, 4153.1 5 T. K. Keenan, J . Phys. Chem., 1957, 61, 1117.16 J.C. Sullivan, D. Cohen, and J. C. Hindman, J . Amer. Chem. SOC., 1957, 79, 4029.17 F. R. Duke and F. R. Parchen, ibid., 1956, 78, 1540.18 J. C. Sheppard and A. C . Wahl, ibid., 1957, 79, 1020.1 9 D. Cohen. J. C. Sullivan, E. S. Amis, and J. C. Hindman, ibid., 1956, 78, 1543.2 0 E. G. Meyer and M. A. Melnick, J . Phys. Chem., 1957, 01, 367p4 GENERAL AND PHYSICAL CHEMISTRY.positive ions of tetra-N-methyl-j5-phenylenediamine by observing thedependence on concentration of the width of the lines of the absorptionband due to proton (lH) resonance.21 The method is applicable tosystems having rate constants greater than 3 x lo3 1. mole-1 sec.-l. Oneof the largest rate constants yet measured, 0.5 x lo8 1. mole-1 sec-1, hasbeen obtained for the cuprous-cupric reaction in hydrochloric acid,22 thenuclear magnetic resonance line width of 63Cu being used.McConnell andBerger 23 have developed a theory for these reactions and have called them" paramagnetic pulse " reactions from the condition that exchange betweenparamagnetic and diamagnetic species results in a change in a large hyperfinemagnetic field acting at one or more of the molecular nuclei. Bloch'sequations 24 were used to establish a quantitative relation between theshape of the nuclear resonance line, nuclear and electron relaxation times,and the reaction rate.Also, variations in line width of electron spin resonance absorptionbands are being used to measure rates of electron exchange between thecomponents of organic redox systems.An example is the broadening ofthe electron spin resonance lines of naphthalene negative ion caused by thepresence of naphthalene; 25 the bimolecular rate constants lie in the range107-109 1. mole-l sec.-l and vary with the solvent and with the alkali-metal ion used.Other isotopic exchange reactioszs. Inorganic reactions in this group havebeen reviewed.6The rates of exchange of ammonia between the solvent liquid ammoniaand ligand ammonia for five metal-ammine cations have been measuredby using nitrogen-15.26 The observed slow exchange for Cr(NH3),3+ andCo(NH3),3+, as compared with the rapid exchanges for Ag(NHJ2+,Cu(NH3),2+, and Ni(NHJe2+, is consistent with their classification as inertinner-orbital complexes.The effect of light on the rate of substitution of H,180 into Cr(H20),3+has been studied at the wavelengths of the three absorption bands of thechromic ion? Reaction probably occurs from an excited electronic staterather than from an excited vibrational state.The formation constants of the ions PtBr,2- and PtBrC2- do not determinethe rate of exchange of radiobromine with ligand bromine.28Iodine-131 being used, isotopic exchange reactions of iodine cyanidewith I- and and iodine chloride with 1230 have been shown to be veryrapid; the mechanism is thought to include molecular association, e.g.,rci + *I, ___L 1(*r2)c1 *IC~ + "11.21 C.R. Bruce, R. E. Norberg, and S. I. Weissman, J . Chem. Phys., 1956, 24, 473.22 H. M. McConnell and H. E. Weaver, ibid., 1956, 25, 307.23 H.M. McConnell and S. B. Berger, ibid., 1957, 27, 230.24 F. Bloch, Phys. Rev., 1946, 70, 460.25 R. L. Ward and S. I. Weissman, J . Amer. Chem. Soc., 1957, 79, 2086.26 H. U. D. Wiesendanger, W. H. Jones, and C . S. Garner, J . Chem. Phys., 1957,27 R. A. Plane and J . P. Hunt, J . Amer. Chem. Soc., 1957, '49, 3343.28 A. A. Grinberg and G. A. Shagisultanova, Izvest. Akad. Nauk S.S.S.R., Otdel.2s F. E. Jenkins and G. M. Harris, J . Phys. Chem., 1957, 61, 249.30 V. L. Pavlov and Yu. Ya. Fialkov, Zhur. obshchei Khim., 1956, 26, 1531.27, 668.khim. Nauk, 1955, 981KINETICS OF CHEMICAL CHANGE. 45The exchange of oxygen-18 between water and sulphuric acid 31 and withsec.-butyl alcohol32 has been studied. In the former system the rate-determining step is the decomposition of sulphuric acid into water andsulphur trioxide and in the latter the slow step is heterolysis of the oxoniumion ROH,+.Formation of benzoyl radicals appears to be essential to the exchangeof carbon-14 between benzoyl peroxide and potassium benzoate in acetone-water mixtures.33 With water as solvent, no significant exchange occurredfor sulphur-35 between sulphate ion and peroxymonosulphuric acid or forcarbon-14 between acetate and peroxyacetic acid and between benzoateand peroxybenzoic acid.=Use of solvents having different dielectric constants affects the rate ofthe ion-dipole reaction of transfer of radioactive iodine between methyliodide and sodium iodide.35Treatment of alkanes with deuterium-labelled sulphuric acid at roomtemperature showed that hydrocarbons with tertiary carbon atoms arecapable of exchange whereas others are n0t.~6 For the exchange of thearylthio-group between ditolyl sulphide and thiocresol in xylene, andbetween dibenzyl sulphide and toluene-a-thiol in decalin, it is believed thatthe activation energy depends upon the dissociation energy of the sulphur-sulphur bond.37Rates of exchange of benzoyl iodide and bromide with elementaryiodine and bromine, respectively, in nonpolar solvents have been measured.38The exchange of isotopically labelled phosphorus and chlorine betweenphosphorus tri- and penta-chloride in carbon tetrachloride has been shownto occur by the mechanism 39 PCl, & PCl, + Cl,.EZectyon exchange between ions of dzflerent metals.These reactions dependmarkedly on the type of anion present, for example, Uvl and FeII areformed from UIV and FeIII in sulphuric acid but the addition of phosphatesbrings about complete reversal.40 This result is consistent with the moreextensive complex-formation by phosphoric acid expected for the ionsU4+ and Fe3+ than for U022+ and Fe2+. Effects of anions are not normallyso spectacular but nevertheless can determine the main reaction path.A detailed study of the reaction between cobaltic ions and cerous ions inperchlorate media led to the conclusion that the rate-determining step isthe reaction of CeC1042+ with CoOH2+; the true activation energy and theentropy of activation were found to be 19 kcal. mole-l and 14 cal. mole-ldeg.-l re~pectively.~~ The cobalt(1n)-thallium(1) reaction has also been31 T.C. Hoering and J. W. Kennedy, J . Amer. Chem. Soc., 1957, 79, 56.33 C. A. Bunton and D. R. Llewellyn, J., 1957, 3402.33 G. Giacometti and A. Iliceto, Biccrca Sci., 1957, 27, 743.3 p G. Levey, D. R. CampbA1, J. 0. Edwards, and J. Maclachlan, J . Amel,. Clcein. Soc.,1957, 79, 1797.35 E. R. Swart and L. J. le Rous, J . , 1957, 406.36 V. N. Setkina, D. N. Kursanov, 0. D. Sterligov, and A. L. Liberman, ProblemyMekhaizizma G Y ~ . Reactsii, Acad. Nauk Ukvain S.S.R., 0tdel.jiz.mat. khim. Nauk, 1953,199.37 E. N. Gur’yanova and V. N. Visil’eva, Zhur.$z. Khim., 1955, 29, 576.38 A. Goldman and R. M. Noyes. J . Amer. Chenz. SOC., 1957, 79, 5370.39 W. E. Becker and R. E. Johnson, ibid., 1957, 79, 5157.4 0 C.F. Baes, J . Phys. Chenz., 1956, 60, 805.41 L. H. Sutcliffe and J. R. Weber, Trans. Faraday SOC., 1956, 52, 122646 GENERAL AND PHYSICAL CHEMISTRY.studied in perchloric acid and is accelerated by the addition of sulphateions.42Kinetic data from the reduction of thallium(II1) by trisdipyridyl-osmium(I1) in perchlorate solutions 43 were interpreted as implying thatT13+ and T10H2+ react with O~(dipy),~+. Chloride ions produce a similareffect to that observed in the thallium(I)-thallium(m) exchange l1 andthe reduction of thallium(II1) by iron(rI).44 A study of the oxidation ofmercury(1) by thallium(II1) in aqueous solution 459 46 led to the postulationthat the slow step is a two-electron transfer between a mercury atom,formed by dismutation of HgZ2+, and a hydrolysed thallic ion; recentlya value of 5-5 x a t 25" has been obtained for the dismutation constantby use of a radioactive tracer te~hnique.~' Formation of complex ionsagain affects the rate; perchlorate ions retard the reaction probably byforming complexes with Hg,2+, whereas complexes between mercuric ionand chloride or bromide ions accelerate the reaction.Kinetic measurements on the system Cr2+ + (NH,),Co(H,0)3+ accom-panied by tracer experiments on the transfer of oxygen show that hydroxylion and probably water are transferred during the reaction.48 It issuggested that this mechanism is a distinct possibility for other aquo-cations undergoing electron transfer.All the reactions quoted in this group have had water as solvent butsome preliminary results have been reported for the systems plumbic withcobaltous, ceric, or manganous ions in acetic acid.4gHomogeneous catalysed reactions.An excellent Review by Halpern 50describes the reactions undergone by molecular hydrogen in solution whenactivated catalytically by metal salts. For the catalysis by cupric saltsin quinoline solution it has been suggested that CuH+ is the active inter-mediate. 51 The catalysis of the homogeneous reduction of pennanganateby hydrogen in aqueous solution is thought to have AgH+ and MnO,,- asintermediates ; 52 however, when dichromate ions are reduced under similarconditions 53 two independent reaction paths appear having the slow steps2Ag+ + H, + 2AgH+ and Ag+ + H, @ AgH + H+.Bawn and his co-workers have continued their work on oxidations oforganic compounds catalysed by metal salts with an investigation of theautoxidation of benzaldehyde in the presence of cobaltous acetate andthe autoxidation of acetaldehyde in the presence of manganous, cupric,and cobaltous all in acetic acid.A similar study has been made42 K. G. Ashurst and W. C. E. Higginson, J . , 1956, 343.43 D. H. Irvine, J., 1957, 1841.44 F. R. Duke and B. Bornong, J. Phys. Chem., 1956, 60, 1015.4 5 A. M. Armstrong, J. Halpern, and W. C. E. Higginson, ibid., p. 1661.413 A. M. Armstrong and J . Halpern, Canad. J. Chem., 1957, 35, 1020.4' H. C. Moser and A. F. Voigt, J. Amer. Chem. Soc., 1957, 79, 1837.4 8 R. K. Murmann, H.Taube, and F. A. Posey, ibid., p. 262.49 L. H. Sutcliffe and J . Walkley, Nature, 1956, 178, 999.5 0 J. Halpern, Quart. Rev., 1956, 10, 463.5L J. Halpern, E. R. Macgregor, and E. Peters, J. Phys. Chem., 1956, 66, 1455.52 A. H. Webster and J . Halpern, Trans. Faraday Soc., 1956, 53, 51.53 Idem, J . Phys. Chem., 1957, 61, 1239.54 C. E. H. Bawn and J. E. Jolley, Proc. Roy. Soc., 1956, A , 237, 293.5j C. E. H. Bawn, T. P. Hobin, and L. Raphael, ibid., p. 313KINETICS OF CHEMICAL CHANGE. 47of the oxidation of liquid cyclohexene catalysed by salts of iron, cobalt,manganese, and copper.56 Reaction between the catalyst and cyclohexenylhydroperoxide to form a complex is the initiation process but in some casesa simultaneous initiation reaction between the catalyst and cyclohexeneis possible.New complexes formed by chelating agents were found to havedifferent catalytic a~tivities.~’ The elimination of catalyst after initiationof oxidation of decane by manganese and cobalt laurates and stearatesdoes not lower the reaction rate.58 Formation of cuprous ions was detectedin the cupric-ion catalysed oxidation in aqueous organic solvents of somehydroxylic organic compounds, e.g., ascorbic acid and quinol, by theretardation caused by the addition of the cuprous complex-forming agent,cuproin. 59It has been deduced from the kinetics of the liquid-phase oxidation ofhydrocarbons that tetraethyl-lead reacts with the peroxides formed.60, 61Changes in redox potentials have been used.to follow the catalyticdecomposition of peroxydisulphuric acid, the most rapid reaction being theformation of H2S0,.62 The effectiveness of silver(1) and copper(I1) isattributed to the formation of higher-valency states.Kinetic data for the curtailment of the activity of sodium molybdatein the catalytic decomposition of hydrogen peroxide by calcium salts havebeen supported by the isolation of two calcium permolybdates.63Cobaltic hydroxide is much more effective than nickelic hydroxide indecomposing sodium hypochlorite in alkaline solution. 64The observed chemical reaction in the photolysis of ceric ion-thallousion mixtures is the oxidation of thallous by ceric The kinetic datacan be interpreted by a mechanism in which thallous ion competes withcerous ion for hydroxyl radicals.This conclusion is supported by resultsfrom the radiolysis of the mixtures with 6oCo radiation.66Other renctiom of oxygen and peroxy-compounds. The reactions ofoxygen with iron(I1) G7 and with plutonium(II1) 68 in sulphuric acid havebeen shown to depend on the sulphate-ion concentration. From theeffect of deuterium oxide on the latter system 69 it has been postulatedthat the transition state is two plutonium(II1) sulphate complexes linkedby an oxygen bridge, ie., transfer of a hydrogen atom is the main process.A chain mechanism is indicated for the autoxidation of liquid 1 : 4-di-methylcyclohexane. The parent hydrocarbon being used as solvent, the6 6 A. J. Chalk and J. F. Smith, Trans. Faruduy SOC., 1957, 53, 1214.5 7 Idem, ibid., p.1235.5 8 D. G. Korre, 2. K. Maims, and N. M. Emanuel’, Zhur. $2. h’him., 1955, 29, 710.5 9 R. Flitman and E. Frieden, J . Amer. Chem. SOL, 1957, 79, 5198.6 O G. S. Shimonaev and I. V. Rozhkov, 2hur.fiz. Khim., 1955, 29, 791.61 Idem, ibid., 1957, 31, 94.6a H. Galiba, L. J . CSanyi, and 2. G. Szab6, 2. anorg. Chem., 1956, 287, 152.63 G. A. Bogdanov, T. I. Berlrengeim, and.V. A. Shcherbinin, 2huv.jiz. Khim., 1956,64 F. M. Perel’man and A. Ya. Zvorykin, ibid., 1955, 29, 980.6 5 T. J. Sworski, J . Amer. Chenz. SOC., 1957, 79, 3655.6 6 Idem, Radiation Research, 1956, 77, 483.67 R. E. Huffman and N. Davidson, J . Amer. Chew SOC., 1956, 78, 4836.6 8 T. TV. Newton and F. B. Baker, J . Phys. Chem., 1956, 60, 1417.6 9 Idem, ibid., 1957, 61, 381.7 0 V.Stannett, A. E. Woodward, and R. T3. Mesrobian, ibid., 1957, 61, 360.30, 88948 GENERAL AND PHYSICAL CHEMISTRY.decomposition of the peroxide derived from it was found to be of the secondorder in peroxide; this is thought to be due to the occurrence of peroxidedimers. The intermediate peroxide formed in the oxidation of decane wasfound to break down to give alcohols and carbonyl compounds as theprincipal products.71 That acids are not formed directly in the productsof the decomposition of the peroxide is supported by the kinetics. At 120"liquid 2 : 5-dimethylhexane and 2 : 4-dimethylpentane gave the corre-sponding peroxides in high yield even though only 10% reaction wasachieved. 72 The results show that intramolecular attack of peroxy-radicalsis highly efficient at the position, somewhat less so at the y position, andof little significance at the o! or the 6 position.The efficiency of intra-molecular oxidation appears to be favoured by attachment of the peroxy-radical to a tertiary carbon atom.Interest in the reactions of hydrogen peroxide with ferrous ion continues ;a fine piece of experimental work by Dainton and Hardwick 73 was directeda t determining the ratio of the rate constant of the reactions of hydroxylradicals with solute (dissolved hydrogen or carbon dioxide) to the rateconstant for the reaction of ferrous ions with hydroxyl radicals. In afurther study of this system, Hardwick 74 has found k,/k, to be 0.116 at20.2" for O.1M-perchloric acid, for the reactions H, + OH __f H,O + H(k,)and Fe2+ + OH __t Fe3+ + OH-(K,). The rate constants 5.3 x lo8exp (-9450/RT) 1.mole-l sec.-l in 1.00M-perchloric acid and 9-6 x losexp (-9750/RT) 1. mole-l secrl in 0-8~-sulphuric acid have been evaluated 75for the reaction between ferrous ions and hydrogen peroxide. The differ-ences between results of previous workers are explained. When glycineis present the course of the reaction is determined by competition betweenferrous ion and glycine for the hydroxyl radi~al.7~ The overall rate ofthe reaction is controlled by the rate of production of the hydroxylradical which in turn depends upon the concentrations of glycine andhydrogen ion.In the reduction of cobaltic perchlorate by hydrogen peroxide 77 evidencewas obtained for the occurrence of the species Co111H02- and its formationconstant was estimated .The appearance of the H02* radical in the decomposition of hydrogenperoxide catalysed by cupric, ferrous, and cobaltous ions has been detectedby means of 2 : 6-di-te~t.-butyl-4-methylphenol, which gives a crystallineproduct.78Radiosulphur has been used in an investigation of the sulphite-per-sulphate reaction;. it was demonstrated that a quarter of the sulphur inthe dithionate produced originated from the per~ulphate.~~ This led to7 1 L. S. Vartanyan, Z. K.Mauzus, and N.M. Emanuel',%hur.jiz. Khim., 1956,30,856.i2 F. F. Rust, J . Amer. Chem. SOC., 1957, '79, 4000.7J F. S. Dainton and T. J. Hardwick, Trans. Faraday SOC., 1957, 53, 333.7.1 T.J. Hardwick, Canad. J . Chem., 1957, 35, 437.76 C. R. Maxwell and D. C. Peterson, J . Amer. Ckem. Soc., 1957, '79, 5110.7 7 J . H. Baxendale and C. F. Wells, Trans. Faraday SOC., 1957, 53, 800.7 8 G. M. Coppinger, J . Amer. Chem. SOC., 1957, '79, 2758.79 A. W. H. Aten, K. P. Louwrier, P. Coppens, H. A. Kok, A. M. de Roos, E. Kriek,Idem, ibid., p. 428.A. Hillege, L. Vollbracht, and F. Hartog, J . Inorg. Nuclear Chem., 1956, 3, 296KINETICS OF CHEMICAL CHANGE. 49the suggestion that the pyrosulphate ion is formed as an intermediate,the mechanism being :03SO~OS032-+ + 0 3 S 0 - * S 0 3 2 - + SO,2-o,so~*so3~- __t O3f*SO*f*SO32-03~*SO*f*S032- $. *so3'- 03f*S**S032- + f*S0,2-The reduction of potassium persulphate by sodium thiosulphate was foundto be accelerated by the addition of potassium nitrate which was ascribedto the catalytic action of potassium ions.80 The rate of the reaction betweenpotassium peroxydisulphate and oxalic acid is independent of the concen-tration of the latter, however; the oxalate is capable of yielding the ionradical C,O,- and initiates chains which cause autocatalysis.81The decomposition of tert.-butyl hydroperoxide in dodecane solutionat 98.5" in a helium-swept system appears not to be a chain reaction nordoes it involve tert.-butoxy-radicals.s2 In a closed system, the rate is veryslow, probably owing to the formation of an unreactive dimer. Generationof the tert.-butoxy-radical in the presence of various types of hydrocarbonhas enabled structure to be correlated with reactivity, account being takenof the steric shielding of reactive groups from attack by the bulky butoxy-radical.83 The rate of decomposition of benzoyl peroxide in alcohols wasfound to increase as the homologous series is descended.@The oxidation of acetaldehyde by peracetic acid is believed to proceedvia an intermediate peroxide of unknown compo~ition.~~ The slow rate ofdisappearance in methanol, nitromethane, and acetone is attributed to theformation of hydrogen bonds by peracetic acid with solvent molecules.86In toluene much higher rates were encountered; in this solvent peraceticacid was found to have an infrared absorption band at 3310 cm.-l corre-sponding to an intramolecular hydrogen bond of the type MeCO*OOH.The reaction between cobaltic ion and tert.-butyl hydroperoxide or thehydroperoxide of 2-methylbut-2-ene is more rapid in dilute sulphuric acidthan in glacial acetic acid.87Oxidations by metal ions.The rate of reduction of cobaltic perchlorateby water is observed to be of the 3/2 order in ColI1 and inversely proportionalto the square of the hydrogen-ion c~ncentration.~' These kinetics areaccounted for by supposing that the cobaltic ions are present mainly asdimers. The oxidation of ethanol by ceric perchlorate in aqueous solutionsis preceded by the rapid formation of a 1 : 1 complex between the reactants,the rate-determining step being decomposition of the complex.88 A8 0 Masaji Miura, Tetsuo Miyata, Sadaichi Otani, Akira Yoltohata, and TamotsuOgawa, J .Sci. Hiroshima Univ., 1956, A , 19, 507.81 S. P. Srivastava and S. Ghosh, 2. phys. Chem. (Leipzig), 1966, 205, 332.82 B. K. Morse, J . Amev. Chew. SOC., 1957, 79, 3375.83 J . H. T. Brook, Trans. Faraday Soc., 1957, 53, 327.S4 Fujio Mashio and Shinichi Kato, M e w Fac. Ind. Arts Kj*oto Tech. Univ., Sci.8 6 R. F. Vasil'ev and N. M. Emanuel', Izvest. Akad. Nauk S.S.S.R., Otdel. khim.8 6 R. F. Vasil'ev, A. N. Terenin, and N. M. Emanuel', ibid., 1956, 403.8 7 J. A. Sharp, J., 1957, 2026.8 8 M. Ardon, ihid., p. 1811.- - - - - - - -ITechmd., 1956, 5, 51.N a u k , 1956, 38750 GENERAL AND PHYSICAL CHEMISTRY.preliminary report has appeared on the reaction between oxalate and cericions in sulphuric acid solutions.sgFormate ion autocatalyses the reduction of permanganate ions by formicacid a t low acid concentration^.^^ Further reduction after reaching theMnIV stage, i.e., MnO,, is explained by a mechanism incorporating themanganate ion.A thorough kinetic study of the oxidation of diphenyl-methanol by potassium permanganate led to the conclusion that thereaction occurs by transfer of a hydride ion H- from the diphenylmethoxideion to the permanganate Evidence has been presented to show thatboth bivalent and tervalent manganese participate in the reduction of thelatter ion by oxalate ions.92 When acraldehyde is oxidised by manganicpyrophosphate the slow step is the acid-catalysed formation of P-hydroxy-propionaldehyde from acraldehyde. 93In dilute sulphuric acid the double bonds of olefins are attacked bycobaltic ions by way of electron transfer; the carbonium ions so producedgive hydroxylic compounds which are rapidly oxidised by cobaltic ions.94These reactions do not take place in glacial acetic acid unless sulphuricacid is added and then different kinetics are obtainedag5 The results areinterpreted as being due to the formation of a stable complex cobalticsulphate-acetate ion.96It has been shown that radicals produced during polymerisation 97 andalso the free radical ad-diphenyl-p-picrylhydrazyl 49 will react with avariety of metal salts in a number of media.Hydrolysis and acid-base equilibria.Carbamic acid and a dimer ofcyanic acid have been suggested as intermediates in the hydrolysis ofcyanic acid.98 The hydrolysis of esters has been studied both for solventeffects S9 and for the effect of substitution into fluorinated esters.100 Thehydrolysis of thioacetamide is catalysed by both acids and bases withthioacetic acid appearing as an intermediate in both reactions.101 Therate of production of acetic acid from acetic anhydride and water found byobservation of magnetic resonance of hydrogen nuclei was in fair agreementwith results from direct titration.lo2 Results for the rates of solvolysisof a series of benzenesulphonates, halides, and methanesulphonates wereobtained by use of light and heavy water as solvents.The difference inrate ratios was put down to differences in the solvation of the initial states.103The acid hydrolyses of cis-[Cr en,Cl,]+ and the corresponding cobalt complex8 9 V.H. Dodson and A. H. Black, J . Amer. CWemSoc., 1057, 79, 3657.9 0 E. Abel, 2. phys. Chem. (Frankfurt), 1956, 8, 127.9 1 R. Stewart, J . Amer. Chem. SOL, 1957, 79, 3057.92 Shigeru Yamashita, Teruo Hayakawa, and Osamu Toyama, Bull. Univ. Osaka93 H. Land and W. A. Waters, J., 1957, 4313.94 C. E. H. Bawn and J. A. Sharp, ibid., p. 1854.95 Idem, ibid., p. 1866.96 J. A. Sharp, ibid., p. 2030.97 E. Collinson and F. S. Dainton, Nature, 1956, 177, 1224.98 A. R. Amell, J . Amer. Chem. Soc., 1956, 78, 6234.100 A. Moffat and H. Hunt, ibid., p. 54.101 D. Rosenthal and T. I. Taylor, ;bid., p. 2684.102 B. N. Bhar and W. Forsling, Arkiv Fys., 1957, 11, 405.103 P. M. Laughton and R. E. Robertson, Canad.J. Chenz., 1956, 34, 1714.Prefect., 1957, 5, 131.G. A. Gallagher, J. G. Miller, and A. R. Day, ibid., 1957, 79, 4324KINETICS OF CHEMICAL CHANGE. 51have similar mechanisms, indicating that they have similar electronic~onfigurations.10~The reaction H+ + OH- ---t H20 has been demonstrated to be thefastest known bimolecular reaction, having a rate constant of 1.3 x loll 1.mole-l sec.-l at 20";f05 a relaxation method was used in which electric fieldsof 105 v/cm. were applied. The application of the acidity functions h, andH , as a diagnostic for the mechanisms of acid-catalysed processes has beendiscussed.106~ 107 The slow step in the acid-catalysed hydrolysis of ethyleneoxide and its derivatives is the production of a carbonium ion which thenreacts rapidly with water to form a glycol and hydrogen ions.lo8Nuclear magnetic resonance methods have been used to study theprotolysis of methylammonium ions in aqueous solution log and acid-baseequilibria in aqueous solutions of alkylamines.l1°Higginson and Marshall have compared theoxidation of sulphurous acid in aqueous solution with that of hydrazineby the same reagents.111 The mechanisms of the reactions are similarsince the products formed depend principally upon whether the oxidisingagent favours a one- or a two-equivalent reaction.The rate of oxidationof sulphite by bromate ions indicates that the reaction proceeds throughtwo different transition states.l12 When chlorate ions bring about theoxidation then the hydroxyl radical and the hydrogen sulphite radical HSO,*are possible intermediates.l13The kinetic data for the oxidation of bromide ions in nitric acid implythat the slow step is the decomposition or rearrangement of a complex ion[N20,BrH] +.l14The aquation of halogenopentamminocobaltic ions is induced by metalions which may donate a water molecule from their hydration shells.115Sulphate ions associate with the reactants and enter the transition state.Methanol was used as solvent for the reaction of some anions with cis-[Co en2C12]+ and trans-[Co (AA),Cl,]+ (where AA is a substituted ethyl-enediamine) to suppress h y d r 0 1 y s i s .l ~ ~ ~ ~ ~ ~ Specific anion effects werefound for the effect of electrolytes on the rate of loss of chloride from[Cr(NH,),C1I2+ in aqueous solution.lls Simple and autocatalytic pathsare present for the reversible formation of complexes from Cr3+ and ~rea.11~The formation and hydrolysis of copper(I1)-pyridine complexes have beenMiscellaneous reactions.I04 J. Selbin and J.C . Bailar, J . Amev. Chew. SOC., 1957, 79, 4285.In5 M. Eigen and L. de Maeyer, Naturwiss., 1955, 42, 413.106 F. A. Long, Pvoc. Chem. Soc., 1957, 220.l n 7 F. A. Long and M. A. Paul, Chem. Rev., 1957, 57, 935.109 E. Grunwald, A. Loewenstein, and S. Meiboom, J . Chem. Phys., 1957, 27, 630.l10 Idem, ibid., p . 641.1'1 W. C. E. Higginson and J. W. Marshall, J., 1957, 447.l J 2 F. S. Williamson and E. L. King, J . Amer. Chem. Soc., 1957, 79, 5397.I L 3 E. H. Gleason, G. Mino, and W. M. Thomas, J .Phys. Chem., 1957, 61, 447.114 J. V. L. Longstaff, J., 1957, 3488.115 F. A. Posey and H. Taube, J . Amer. Chem. Soc., 1957, 79, 255.116 R. G. Pearson, P. M. Henry, and F. Basolo, J . Amer. Chem. Soc., 1957, 79, 5379.1 1 ' Idem, ibid., p . 5382.118 &I. Ikuta, H. G. McAdie, and W. MacF. Smith, Canad. J . Chem., 1956, 34, 1361.'19 K. B. Yatsimirskii and E. I. Yasinkene, Zhur. neorg. Khim., 1956, 1, 438.F. A. Long, T. G. Pritchard, and F. E. Stafford, J . Amer. Chem. Soc., 1957,79, 236252 GZNERAL AND PHYSICAL CHEMISTRY.investigated.120 Reactions of some platinum(I1) complexes with a varietyof nucleophilic reagents have been reported.121The absorption of ethylene by sulphuric acid is catalysed by copper,mercury, and silver salts.122A gradual change in the mechanism is postulated for the reactionscatalysed by gallium bromide of some alkyl bromides with benzene andtoluene in which the carbonium-ion character of the transition state increaseswith increasing branching of the alkyl g r o ~ p .1 ~ ~The stable intermediate SnCl,,C,H,Cl is involved in the exchange ofchlorine36 between stannic chloride and 2-chlorobutane in heptane.124A combination of organic reagents and radioactive isotopes has beenapplied to the study of reactions in very dilute solutions, i.e., 10-7-lo-9~;an example is the thallous-ferric r e a ~ t i 0 n . l ~ ~In September 1956 the Faraday Society held adiscussion on “ The Physical Chemistry of Processes at High Pressures ”at Glasgow University when several papers were read dealing with theeffect of pressure on chemical reactions.Laidler discussed the factorsinfluencing overall volume changes and volumes of activation for ionicreactions in water.126 The rates of dissociation of ctd-azoisobutyronitrileand pentaphenylethane have been measured in toluene at pressures up to10,000 and 1500 atm. respectively, and were found to be decreased bypressure. The effect of pressure on the dissociation equilibrium of dinitrogentetroxide in carbon tetrachloride at pressures up to 1500 atrn. was foundto be ten times as great as predicted from the changes in molecular volunie.127The acceleration by pressure of the rates of interconversion cis- and trans-1 : 2-dichloroethylene catalysed by iodine can be attributed to the increasedrate a t which iodine atoms add to the double bonds.128 Results from thedecomposition of benzoyl peroxide in carbon tetrachloride at high pressurelead to the conclusion that the effect of pressure on the rate of initiation inthe peroxide-catalysed polymerisation of styrene is ~ n i a l l .1 ~ ~A new method of kinetic analysis for reactions occurring at the air-solution interface has been developed and applied to the surface hydroxyl-ation of polyisoprenes by acidified perinanganate s0lution.1~0An attempt has been made to formulate a theory of Iiquid-phasereactions by use of the methods of non-equilibrium statistical mechanics.131It is shown that the theory gives rates no less satisfactory than thosecalculated from the transition-state theory for the reaction between bromideions and alkyl bromides.Laidler and Landskroener have developed aNo%-chemical e#ects.120 D. L. Leussing and R. C. Hansen, J . Amer. Chevn. Soc., 195?, 79, 4270.121 D. Banerjea, F. Basolo, and R. G. Pearson, ibid., p. 4055.122 M. Hellin and J. C. Jungers, Bull. Scc. chirn. France, 1957, 386.123 C . R. Smoot and €1. C . Brown, J . A Y ~ E Y . Chew SOC., 1956, 78, 6249.124 R. A. I-Iowald and J. E. Willard, ibid., p. 6217.lz5 V. I. Kuznetsov and G. V. Myasoedova, Zhur. neovg. Khim., 1956, 1, 579.126 K. J. Laidler, Discuss. Fnraday Soc., 1956, 22, 89.12’ A. EI. Ewald, ibid., p. 138.128 A. H. Ewald, S. D. Hamann, and H. E. Stutchbury, Trans. Faraday Soc., 1957,129 A. E. Nicholsoii and R. G. W.Norrish, Discuss. Faraday SOC., 1956, 22, 97.130 W. R. Dean, V. Perera, and J. Glazer, Trans. Faraday SOL, 1957, 53, 679.131 J. L. Wood and A. Suddaby, ibid., p. 1437.53, 991KINETICS OF CHEMICAL CHANGE. 53theory which relates rate constants to the dielectric constant of the solventfor reactions in which electrostatic interactions predominate.132The lack of convincing experimental evidence to support the Brgnstedtheory of the kinetic salt effect caused Barrett and Baxendale133 to studythe effect of a variety of salts on the rate constant of the reaction betweenferrous ion and CO(C,O,),~- in water. Good agreement with the theory wasobtained for ionic strengths up to 4 x 10-3~. Application of the positivesalt effect of sodium chloride on the reaction between peroxydisulphateand iodide ions has been used to calculate the ionic radius of the activationcomplex.134The methods of preparation, structure, andproperties of polyethylene,l graft copolymers,2, and block copolymers 49have been extensively reviewed, and Mandelkern has reviewed the kineticsand general features of the crystallisation of flexible polymer molecules.The theoretical treatment of stereoisomerism in high polymers has beenextended by Arcus to include alternating copolymers and the conditionsfor optical activity therein.A British Patent to the Standard Telephone and Cable Co.dis-closes one of the first successful formations of a high polymer from a 1 : 2-di-substituted ethylene (other than highly fluorinated olefins) .The monomerused was 1 : l-dichloro-2-fluorovinyl methyl ether and polymerisation waseffected by addition of boron trifluoride in liquid propane or butane, thereaction being allowed to take place at the boiling point of the solvent.The polymer is stated to be a rubber-like substance with a softening pointwell above 250".has been usedas a method for estimation of the monomer even when it is mixed withother olefins.Young's modulus of semicrystalline polymers has been consideredtheoretically 10 and comparison of calculated and experimental values fortwo widely different polyethylene samples leads to the conclusion thatcrystallite sizes in slowly cooled polyethylene vary from 250In contrast with the normal heterogeneous copper-catalysed poly-merisation of diazoalkanes, a homogeneous system has been reported 11in which the catalyst is a cuprous iodide-amine mixture.Polyethylideneas usually obtained from the polymerisation of diazoethane is a completelyamorphous substance with m. p. ca. go", but Saini, Campi, and Parodi12Polymerisation.-General.The quantitative polymerisation of 14C-labelled ethyleneto 400 A.132 K. J . Laidler and P. A. Landskroener, Tvuns. Faraday Soc., 1957, 53, 200.133 J. Barrett and J. H. Baxendale, ibid., 1956, 52, 210.134 G. M. Schwab and S. Krawczynski, 2. Plzys. Chem. (Fvankfurt), 1956, 8, 1.1 S. L. Agganval and 0. J. Sweeting, Chem. Rev., 1957, 57, 665.2 N. G. Gaylord, Intei.chem. Rev., 1956, 15, 91.3 R. Hart, I n d . chim. belge, 1956, 21, 1053, 1193.4 N.G. Gaylord, Intevchenz. Rev., 1957, 16, 3.5 R. Hart, Ind. chirn. belge, 1956, 21, 1309.6 L. Mandelkern, Chenz. Rev., 1956, 56, 903.7 C. L. Arcus, J . , 1957, 1189.8 B.P. 754,976, Standard Telephone and Cable Co.Q F. Danusso, G. Pajaro, and D. Sianesi, J . Polymer Sci., 1956, 22, 179.10 F. Bueche, ibid., p. 113.11 C . E. H. Bawn and A. Ledwith, Chem. and Ind., 1957, 1180.12 G. Saini, E. Campi, and S. Parodi, Gazzetta, 1957, 87, 34254 GENERAL AND PHYSICAL CHEMISTRY.have succeeded in preparing a crystalline polyethylidene with an m. p.above 150" by use of colloidal gold as a catalyst. It is thought that thecrystalline form of polyethylidene is produced by the influence of theheterogeneous catalyst site, i.e., colloidal gold. The preparation of thishigh-melting form of polyethylidene has been confirmed independently byBawn and Ledwith.llThe successful transformation of cis-I : 4 units in polybutadiene intocorresponding trans units has been accomplished by means of ultravioletirradiation of the polymer in the presence of a suitable sen~itizer.1~ Howeverisomerisation could not be induced in natural rubber.The molecular structure of polyethylene has been much studied 1% 15 andit has been shown l6 that when short-chain branching is corrected for, theviscosity of molten polyethylene obeys the Fox and Flory law, qM= Mi:.No simple relation between either solution viscosity or melt viscosity withnumber-average molecular weight could be found for polyethylene,l7 andNicholas 18 has amended the Harris equation relating intrinsic viscosityand molecular weight of unfractionated high-pressure polyethylenes.Astudy of the non-Newtonian behaviour of poly(viny1 acetate) solutions hasshown19 that the value of the Huggins constant k' at zero rate of shearis independent of molecular weight for a given polymer and is a fundamentalproperty associated with the inherent character of the polymer chains andtheir interactions with the solvent at a particular temperature. Otherstudies20 on the same monomer have indicated that k' is measurablysensitive to branching only for fractions possessing a certain minimumcombination of size and complexity.It was shown 21 that the absolute value of the turbidity of benzene asdetermined by Carr and Zimm is more correct than the earlier value deter-mined by Cabannes.Light-scattering measurements 22 in some branched polystyrenes ofknown structure have shown that the molecular weights and dimensionscalculated therefrom are in satisfactory agreement with the known structureof the polymers.Intrinsic viscosity-molecular weight relations have been establishedfor poly-4-vinylpyridine z3 and poly(chlorotrifluoroethy1ene) .24Fyee-radical polymerisation.Mixtures of salts of NN-dialkylaryl-amines and o-sulphobenzoic imide (saccharin) have been shown25 to beefficient initiators for the polymerisation of methyl methacrylate and13 M. A. Golub, J . Polymer Sci., 1957, 25, 373.14 L. T. Muus-and F. W. Billmeyer, jun., J . Amer. Chem. SOL, 1957, 79, 5079.15 Q.A. Trementozzi, J . Polymer Sci., 1956, 22, 187.16 W. L. Peticolas and J. M. Watkins, J . Amer. Chem. Soc., 1957, 79, 5083.17 C. E. Ashby, J . S. Reitenour, and C. F. Hammer, ibid., p. 5086.1s L. Nicolas, Makromol. Chem., 1957, 24, 173.l o S. L. Kapur and S. Gundiah, J . Polymer Sci., 1957, 26, 89.20 L. M. Hobbs, S. C . Kothari, V. C. Long, and G. C. Sutaria, ibid., 1956, 22, 123.21 P. Rempp and H. Benoit, ibid., 1957, 24, 155.22 M. H. Jones, H. W. Melville, D. W. Ovenall, F. W. Peaker, and IV. G. P. Robed-23 A. G. Boyes and U. P. Strauss, J . Polymer Sci., 1956, 22, 463.24 E. K. Walsh and H. S. Kaufman, ibid., 1957, 26, 1.26 J . Lal, R. Green, and S. Ellis, ibid., 1957, 24, 75.son, J . Colloid Sci., 1956, 11, 508KINETICS O F CHEMICAL CHANGE.55acrylonitrile. The decomposition of peroxy-carbamates has been studiedin order to determine their efficiencies as initiators of vinyl polymerisationand it was shown 26 that during the decomposition of tert.-butyl N-phenyl-peroxycarbamate (between 50" and 90") both tert.-butoxy- and phenyl-amino-radicals efficiently initiate chains.Initiation of polymerisation of styrene has been achieved by use ofelectrons supplied at a cath0de.~7 The photopolymerisation of acrylonitrilein magnesium perchlorate solution has been studied with ferric salts asinitiators.28 Dialkylsilanes have been used to initiate the polymerisationof t et rafluoroet hylene .29 Other aspects of radiochemical polymerisationare discussed in the section on Radiation Chemistry (p.68).Use of 14C-labelled benzoyl peroxide as initiator in the polymerisationof styrene shows that the fraction of initiating radicals which are benzoyloxydecreases as the monomer concentration is reduced.30The kinetics of the polymerisation of styrene and methyl methacrylateinitiated by di-terf.-butyl peroxide have been studied 31 between 60" and 98".Ethyl methyl ketone peroxide has been used32 as an initiator for thepolymerisation of several vinyl monomers and the specific rate constantsfor spontaneous and induced decomposition have been determined at 70"and 80". It was found that this initiator is comparable to benzoyl peroxideand azoisobutyronitrile in its catalytic efficiency, while its capacity fortransfer is intermediate between those of non-transferring azoisobutyronitrileand highly transferring cumene hydroperoxide.The polymerisation of acrylamide initiated by X-rays and y-rays hasbeen studied kinetically 33 along with the hydrogen peroxide-photosensitizedpolymerisation 34 at 25". Riboflavin being used as ~ensitizer,~~ the photo-polymerisation of this monomer is very fast; the rate depends upon thesquare root of the viscosity of the medium.The polymerisation of ethylene at 7000 atm.initiated by azoisobutyro-nitrile or benzoyl peroxide produces a substantially linear, high-melting(m. p. 131") polyethylene of high density.36Heat and entropy changes for the polymerisation of methacrylonitrilehave been calculated from a study of the photosensitized reaction at tem-peratures above 100".The results suggest that depolymerisation isimportant at these temperature^.^'Thomas and Webb3s suggest that the best value for the propagation2 6 E. L. O'Brien, F. M. Beringer, R. B. Mesrobian, J . -4mer. Chenz. SOC., 1957,27 J. Y. Yang, W. E. McEwen, and J. Kleinberg, ibid., p. 5833.28 Y . Grobe and E. Spode, Naturwiss., 1957, 44, 560.29 A. M. Geyer and R. N. Haszeldine, J., 1957, 1038.30 J. C. Bevington, Proc. Roy. Soc., 1957, A , 239, 420.31 J. A. Offenbach and A. V. Tobolsky, J . Amer. Chem. Soc., 1957, 79, 278.32 M. R. Gopalan and M. Santhappa, J . PoZymer Sci., 1957, 25, 333.33 E. Collinson, F. S. Dainton, and G. S. McNaughton, Trans. Faraduy Soc., 1957,34 F. S. Dainton and M. Tordoff, ibid., p.499.35 G. K. Oster, G. Oster, and G. Prati, J . Amer. Chem. SOC., 1957, 79, 595.36 R. A. Hines, W. M. D. Bryant, A. W. Larchar, and D. C. Pease, Ind. Eng. Chem.,37 S. Bywater, Canad. J . Chem., 1957, 35, 552.3s W. M. Thomas and R. L. Webb, J . Polymer Sci., 1957, 25, 124.79, 6238.53, 476, 489.1957, 49, 107156 GENERAL AND PHYSICAL CHEMISTRY.rate of the polymerisation of acrylonitrile in aqueous suspension at roomtemperature is 2 x lo4 1. mole-l sec.-l. The polymerisation of acrylo-nitrile, methacrylonitrile, and styrene in dimethylformamide has beenstudied in the presence of ferric chloride.39 In each case the participatingradicals enter into a termination reaction with the salt, with reduction toferrous chloride. Estimation of ferrous ion provides a convenient methodof determining the rate of starting of chains.Polymerisation of acrylo-nitrile in the presence of lithium salts 40 shows that the coefficients for thepropagation reaction and the transfer reactions to triethylamine and carbontetrabromide are functions of the concentration and nature of the added salt.' Monodisperse ' (polymer of nearly homogeneous molecular weight)polystyrene has been prepared by controlling the time of growth of poly-merising styrene radicals.41 This was achieved by adding excesses of freeradicals a t intervals to an emulsion system. Styrene chains initiated inone addition are then mostly terminated in the next addition. The timeof growth of the polymer chains is the interval between additions and inthis manner polystyrene samples having molecular weights between 500,000and 1,000,000 can be obtained.The polymerisation of styrene initiated by azoisobutyronitrile andbenzoyl peroxide in the presence of natural rubber 42 has been used to deter-mine the chain-transfer constants of styrene to natural rubber.Chain-transfer constants of methyl methacrylate with fourteen solvents have beendetermined at 60" and 80" with azoisobutyronitrile as initiator.43 Graftcopolymers have been obtained by polymerisation of acrylamide in thepresence of natural rubber and by the polymerisation of methyl meth-acrylate in the presence of polyi~oprene.~~Vinyl bromide, which normally produces homopolymer of only lowmolecular weight, has been successfully copolymerised with methylmethacrylate and styrene to give relatively stable compounds of highmolecular weight ,46 and ally1 alcohol, another monomer which yields onlylow homopolymer, has been copolymerised with acrylonitrile to produce apolymer of relatively high molecular weight .47 The reactivity ratios weredetermined for the latter reaction.From a study of the copolymerisationof vinylidene cyanide with a series of olefinic monomers Ham 48 concludesthat acrylonitrile is anomalous in that it gives rise to repulsive effects, whilstother monomers containing methylenic double bonds behave normally.Two new monomers, I : 2-dimethylenecyclohexane 49 and vinyl tri-fluoroacetate, 50 have been polymerised to products of high molecular weightwith typical free-radical initiators.39 C.H. Bamford, A. D. Jenkins, and R. Johnston, Proc. Roy. Soc., 1957, A , 239, 214.4 O Idem, ibid., 1957, A , 241, 364.4 1 J. P. Bianchi, F. P. Price, and B. H. Zimm, J . Polymer Sci., 1957, 25, 27.42 Y . Minoura, Y. Mori, and M. Imoto, Makromol. Chew., 1957, 24, 205.43 R. N. Chadha, J. S. Shukla, and G. S. Misra, Trans. Faraday Soc., 1957, 53, 240.44 G. Oster and 0. Shibata, J . Polymer Sci., 1957, 26, 233.4 5 P. W. Allen and F. M. Merrett, ibid., 1956, 22, 193.4G G. Blamer and L. Goldstein, ibid., 1957, 25, 19.4 7 G. Oster and Y. Mizutani, ibid.. 1956, 22, 173.48 G. E. Ham, ibid., 1957, 24, 349.4 9 A. T. Blomquist and D. T. Longone, J . Amer. Chem. Soc., 1957, 79, 3916.5 O H. C. Haas, E. S. Emerson, and N.W. Schuler, J . Polymer Sci., 1956, 22, 291KINETICS OF CHEMICAL CHANGE. 57The use of ionizing radiationsto initiate, degrade, and graft polymer chains has been briefly reviewed 51and Grassie 52 has reviewed the r61e of abnormal linkages in polymerdegradation. The result of irradiation of polymers has been shown to beconsiderably affected by temperature 53 and the presence of oxygen.=Irradiated polymers, presumably containing active free-radical sites, havebeen used to initiate the polymerisation of 1%-labelled acrylonitrile 55 andthus to determine the degree of grafting.By a study of the degradation of polystyrene and cellulose, Bryce andGreenwood56 have shown that changes in intrinsic viscosity [q] are notthemselves a true measure of the degradation rate and that the often-quoted apparent limit in [q] or (qSp/c) is fallacious.A series of elementary processes for cross-linking and scission reactionsduring the irradiation of polymers have been suggested and consideredtheoretically on the basis of free-radical intermediates.57 Two differentmechanisms have been suggested for the mechanism of the radiation cross-linking of polyethylene : one involves vinylene groups as cross-linkingintermediates 5 8 3 5 9 and the other 6o is based upon intermediates of cationtype.Pyrolysis of polymers and copolymers of styrene and di- and tri-vinyl-benzene indicates that the thermal stability of the polymers increases withthe degree of cross-linking,61 and it has also been shown 62 that the rapidinitial fall in molecular weight of polystyrene samples during thermaldepolyrnerisation is due to disproportionations at weak Links.The cross-linking and degradation of seven polyacrylates have been studied underthe influence of 1000 kvp electrons 63 and it is believed that the presenceof a hydrogen atom alpha to the alcoholic oxygen of the ester group contri-butes strongly to the cross-linking reactions, although it was shownconclusively that no cross-linking occurred during the degradation ofpoly(methy1 me thacrylate) under the same influence.@The number of scissions in poly(methy1 methacrylate) for a given doseof y-irradiation is decreased by the presence of air, small amounts of benzene,and by lowering the temperature to -196". Furthermore it was suggestedthat when Folystyrene is similarly treated the phenyl rings are involved in~ross-linking.~~ Further studies have been made of the ceiling temperatureof polymerisation, and Cook and Ivin have studied the equilibrium betweenPolymer degradation and depolymerisation.51 F.S. Dainton, J . Oil Colour Chemists' Assoc., 1957, 40, 830.52 N. Grassie, Cheun. and Iizd., 1957, 537.53 A. Charlesby and W. H. T. Davisson, ibid., p. 232.64 P. Alexander and D. Toms, J . Polymer Sci., 1956, 22, 343.6 5 J. C. Bevington and D. E. Eaves, Nature, 1956, 1'9.8, 1112.5ti W. A. J. Bryce and C . T. Greenwood, J . Polymer Sci., 1957, 25, 480.57 R. Simha and L. A. Wall, J . Phys. Chetn., 1957, 61, 425.58 R. W. Pearson, J . Polymer Sci., 1957, 25, 189.F 9 M.Dole, D. C. Milner, and T. F. Williams, J . Amer. Clzem. Soc., 1957, YO, 4809.6 o 13. G. Collyns, J. F. Fowler, and J. Weiss, Chem. and I n d . , 1957, 74.61 F. H. Winslow and W. Matreyek, J . Polymer Sci., 1956, 22, 315.N. Grassie and W. W. Ken, Trans. Faraday SOL, 1957, 53, 234.O3 A. R. Shultz and F. A. Bovey, J. Polymer Sci., 1956, 22, 485.64 A. R. Shultz, P. I. Roth, and G. B. Rathmann, ibid., p. 495.6 5 L. A. Wall and D. W. Brown, J. Phys. Chem., 1957, 61, 12958 GENERAL AND PHYSICAL CHEMISTRY.ethyl methacrylate and its polymer; 66 McCormick 67 has found the ceilingtemperature of ct-methylstyrene to be 61” and has shown that the valuedepends only upon the monomer concentration.Condensation polymerisation. The apparently different interpretations 68of the kinetic behaviour of the polymerisation of N-carboxyanhydridesinitiated by amines have been shown 69 to be due to slight variations in thepurity of the monomeric N-carboxyanhydride. Other work 70 on thepolymerisation of N-carboxyanhydrides initiated by amines shows thatthe two successive rate constants, k,, slower, and k2b faster, can be correlatedwith the formation of low- and high-molecular weight polypeptides, res-pectively, and that the polymerisation proceeds at two successive ratesfollowing a very rapid initiation.71 It was also shown 72 that the aminegroups are mostly preserved throughout the polymerisation but are losteasily, during polymer isolation, by cyclisation of the end-groups.A rapid titration method has been developed 73 for the estimation ofprimary mine and carboxyl end-groups in polyhexanolactam which givesresults in satisfactory agreement with those calculated from measurementsof solution viscosity. The influence of water on the degree of polymerisationof polyhexanolactam is reduced by increasing the concentration of“ stabiliser.” 74 The molecular-weight distribution in the last stage of thehydrolytic polymerisation of 6-hexanolactam is characterised by theequilibrium in the polymerisation, depolymerisation, and transamidationreaction^,^^ and this result is identical with the distribution designated byFlory 76 as most probable.From a study of the intrinsic viscosity of the polyesters of 9 : 10-di-hydroxyhexadecane-1 : 16-dicarboxylic acid it was concluded 77 thatbranching or the formation of a three-dimensional network had occurred.The rate of isomerisation of but-2-ene by theboron trifluoride-water complex in ethylene &chloride is given by theexpression : As the concentration ofwater is increased the rate rises to a maximum and then decreases.7s Theionisation of triphenylmethyl chloride in various solvents has been investi-gated ~pectrophotometrically.~~ The cationic polymerisation of styrenein the presence of poly-9-methoxystyrene produces a graft copolymer.8oThe equilibrium polymerisation of an olefinic monomer in the presenceG 6 R. E. Cook and K. J. Ivin, Tram. Faraday Soc., 1957, 53, 1132.67 H. W. McCormick, J . Polymer Sci., 1957, 25, 488.68 D. 6. H.Ballard and C. H. Bamford, J . Amer. Chem. Soc., 1957, 79, 2336.60 P. Doty and R. D. Lundberg, ibid., p. 2338.70 M. Idelson and E. R. Blout, ibid., p. 3948.71 R. D. Lundberg and P. Doty. ibid., p. 3961.72 J. C. Mitchell, A. E. Woodward, and P. Doty, ibid., p. 3955.73 V. A. Mvagkov and A. B. Pakshver, Zhur. Qriklad. Khim., 1956,29, 1703; Chem.Cationic polymerisation.Rate = R[BF,] [BF,,H,O] [Butene].Abs., 1957, 51: 4315.74 T. G. Majury, J . Polymer Sci., 1957, 24, 488.7 5 2. MenEik. Chem. Listv. 1957, 51. 823; Chem. Abs., 1957, 51. 12536.7 6 P. J . Flory, “ Principles of -Polymer Chemistry,” Cornell Univ. Press, Ithaca,7 7 P. R. Bhattacharya, J . Sci. I n d . Res., India, 1956, 15, B, 721.7 8 J. M. Clayton and A. M . Eastham, J . Amer. Chem. Soc., 1957, 79, 5368.7 u A.G. Evans, I. H. McEwan, and J. H. Thomas, J., 1957, 4644.8 0 H . C. Haas, P. M. Kamath, and N. W. Schuler, J . Polymer Sci., 1957, 24, 85.New York, 1953, p. 321KINETICS OF CHEMICAL CHANGE. 59of an ionic initiator has been considered theoretically 81 and it is shown thatthe equilibrium degree of polymerisation p , is not solely a function of thefractional conversion, as in condensation polymerisation.A kinetic investigation of the polymerisation of alkyl vinyl ethers,catalysed by the boron trifluoride-ether complex,82 has shown that anincrease in the dielectric constant increases the rate of polymerisation butdecreases molecular weight ; addition of water lowers the molecular weightwithout affecting the rate of polymerisation. It is suggested that initiationis caused by an ethyl cation from the catalytic species Etf*BF3*OEt-.Thecationic polymerisation of the vinyl ethers has been briefly re~iewed.8~Study of the polymerisation of ethylene oxide catalysed by stannic chlorideshows that two polymer molecules are produced for each molecule of catalystand that chain termination occurs with catalyst destruction and no chain-transfer. The polymerisation catalysed by boron trifluoride, however,yields much dimer owing to the extensive occurrence of chain-transferwithout consumption of catalyst.84 The introduction of 9-methoxy-groups into styrene increases the reactivity of the double bond by a factorof 400. Consequently, chain-transfer and branching are reduced andpoly-P-methoxystyrene is more linear than polystyrene.85 The kineticsof the polymerisation of a-methylstyrene catalysed by boron trifluoride-ether-water complex and the kinetics and mechanism of the polymeris-ation of styrene catalysed by the chloroacetic acids 87 have been studied.Polymerisation of isobutene in ethyl chloride catalysed by aluminiumtrichloride shows a clear-cut dependence of molecular weight on catalystconcentration. The molecular weight passes through a maximum as thecatalyst concentration is increased and the position and height of thismaximum are very sensitive to traces of hydroxylic impurity.88 Thepolymerisation of benzyl perchlorate and some substituted benzyl per-chlorates is thought to proceed by a carbonium-ion mechanism.89High-energy radiation has been used to polymerise isobutene at lowtemperatures and it was therefore concluded that carbonium ions areproduced by irradiation and initiate the polymerisation.The evidencefor this conclusion is not decisive, however, since the polymerisation isinhibited by oxygen and by quin01.~~Afzionic and stereospeciJic polymerisation. The polymerisation ofa-methylstyrene initiated by metallic sodium, in the absence of oxygen,has been described 91 and the properties of the polymer compared with thoseof polystyrene. The suggested mechanism for the anionic polymerisationof vinyl monomers initiated by electi-on-transfer from the sodium-naphthaleneA. V. Tobolsky, J . Polymer Scz., 1957, 25, 220.88 J . D. Coombes and D.D. Eley, J., 1957, 3700.83 D. D. Eley, J . Oil Colour Chemists’ Assoc., 1957, 40, 810.a4 D. J. Worsfold and A. M. Eastham, J . Amer. Chem. Soc., 1957, 79, 897, 900.n5 I-’. M. Kamath and H. C. Haas, J . Polymer Sci., 1957, 24, 143.D. J . Worsfold and S. Bywater, J . Amer. Chem. Soc., 1957, $9, 4917.B 7 C. P. Brown and A. R. Mathieson, J., 1957, 3608-3639.8 8 2. Zliimal, L. Ambroi, and K. Veseljr, J . Polymer Sci., 1957, 24, 286.B9 P. F. G. Praill, J . , 1957, 3162.W. H. T. Davison, S. H. Pinner, and R. Worrall, Chem. and Ind., 1957, 1274.91 G. D. Jones, R. E. Friedrich, T. E. Werkema, and R. L. Zimmerman, Ind. Eng.Cheni., 1956, 48, 212360 GENERAL AND PHYSICAL CHEMISTRY.complex leads to the prediction that the degree of polymerisation isgiven by the ratio [monomer] : [t x catalyst].This prediction has beenverified experimentally for polybutadiene, polyi~oprene,~~ and poly-styrene.93 In the case of the last polymer it was also possible to show thatthe number-average and weight-average molecular weights were approxi-mately equal, also as required by the mechanism suggested by S ~ w a r c . ~ ~The polymerisation of vinyl monomers by boron trialkyls is thought to beanionic in character. A solution of triethylboron in hexane is an effectiveinitiator for the polymerisation of acrylonitrile, methyl methacrylate, vinylchloride, and vinyl acetate 95 and tributylboron has been used to initiatethe polymerisation of styrene, acrylonitrile, and methyl methacrylate. 96It was also found that the tributylboron-catalysed polymerisation ofacrylonitrile was considerably activated by the addition of 2 moles yo ofboron trifluoride-ether complex.97The polymerisation of isoprene initiated by organo-alkali compoundshas been much studied and it appears that the structure of the polymerdepends upon the solvents 9 8 9 9 9 and the alkali metal loo used. When thepolymerisation initiated by lithium metal or lithium alkyls is carried outin benzene or heptane, a precipitate forms and the polymerisation appearsto take place as a surface reaction. This type of heterogeneous poly-merisation produces a polyisoprene with more than 90% of cis-1 : 4structure.98 If the polymerisation initiated by lithium or lithium alkylsis carried out in ether 98 or tetrahydr~furan,~g an apparently homogeneoussystem results and the polyisoprene is a mixture of 3 : 4 and 1 : 2 units.The use of phenylsodium or benzylsodium as initiator loo produces inheptane (i.e., a heterogeneous system) a polyisoprene containing 83% of3 : 4-units, while in tetrahydrofuran solution (i.e., a homogeneous system)the polymer contains 79% of trans-1 : 4 units.The stereospecific polymerisation of olefins is extensively studied inmany countries, but so far most of the published information comes fromNatta’s laboratory in Milan. He has reviewed the progress in this fieldin several publications.101-104 Other reviews of Ziegler-type polymerisationhave been p u b l i ~ h e d , ~ ~ ~ , ~ ~ ~ and Eirich and Mark lo7 have consideredtheoretically the heterogeneous polymerisation of olefins.Details of a92 H. Brody, M. Ladacki, R. Milkovitch, and M. Szwarc, J . Polymer Sci., 1957,25, 221.93 R. Waack, A. Rembaum, J. D. Coombes, and M. Szwarc, J . Amer. Chem. Soc.,1957, 79. 2026.B4 M. Szwarc, Nature, 1956, 178, 1168.g5 J. Furukawa, T. Tsuruta, S. Inoue, J . PoZymer Sci., 1957, 26, 234.9 6 G. S. KoIesnikov and N. V. Klimentova, Izvest. Akad. Nauk S.S.S.R., Otdel.9 7 G. S. Kolesnikov and L. S. Fedora, ibid., p. 236; Chem. Abs., 1957, 51, 11291.9 5 H. Hsieh and A. V. Tobolsky, J . Polymer Sci., 1957, %, 245.99 H. Hsieh, D. J. Kelley, A. V. Tobolsky, ibid., 1957, 26, 240.100 H. Morita and A. V. Tobolsky, J . Amer. Chem. Soc., 1957, 79, 5853.G. Natta, Mod. Plastics, 1956, 34, 169.102 Idem, Chimica e Industria, 1956, 38, 751.103 Idem, Chimie et Industrie, 1957, 77, 1009.104 Idem, Chem.and Ind., 1957, 1520.105 E. G. Curphey, Brit. Plastics., 1957, 486.108 F. Eirich and H. Mark, J . Colloid Sci., 1956, 11, 748.107 Idem, Kunststoffe-Plastics, 1956, Hft. 2.khim. Nauk, 1957, 652; Chem. Abs., 1957, 51, 15458KINETICS OF CHEMICAL CHANGE. 61laboratory study of the Phillips low-pressure process for the polymerisationof olefins have been published together with a review of the normal-pressurepolymerisation of ethylene by aluminium alkyls.losThe stereospecific polymerisation of propene to isotactic polymers, withthe system AlEt,-TiCl, as catalyst, has been studied in detail.log~l10 Therate of polymerisation depended on the partial pressure of propene, theconcentration of titanium trichloride, and the temperature.It was con-cluded that the polymerisation was truly heterogeneous, and with stabilisedcatalysts the rate of polymerisation was constant for a given partial pressureof propene. The activation energy for the polymerisation is 12-14 kcal.mole-] and the effect of variables on the molecular weight and stereoisomericcomposition has been determined. Similar studies were made on thesystem propene-trie thylaluminium-tit anium tetrachloride l11 and it wasfound that the catalyst loses 75% of its activity within 40 minutes ofits preparation. The best rates of polymerisation were obtained with themolar ratio AlEt, : TiC1, = 2 : 1 but greatest stereospecificity was obtainedwith the molar ratio 3 : 1.The requirements for the formation of isotacticpolymer in such systems and the effect of using titanium compounds, otherthan TiCl,, have been discussed.l12~ 113Polymerisation of isobutene in the presence of triethylaluminium andtitanium tetrachloride was most efficient at low temperatures and thepolymer produced did not correspond to conventional polyisobutene sinceit contained one methyl side-chain on every third carbon atom.ll4Polybutadiene has been prepared by use of a catalyst made from triethyl-aluminium and chromium acetylacetone derivative.l15 When the molarratio A1 : Cr was less than 6, syndiotactic * poly-1 : 2-butadiene was obtained.If the ratio was greater than 6 however, isotactic poly-1 : 2-butadiene wasthe principal product.Isoprene can be polymerised by using a catalyst made from triethyl-aluminium and titanium tetrachloride to give a polyisoprene resemblingnatural rubber in that it contains more than 90% of cis-1 : 4 enchainment.Optimum conditions for this polymerisation are a molar ratio A1 : Ti = 1,and when this ratio exceeded 2 no polymer was obtained.ll6Nat ta has concluded 115 that the active Ziegler-type polymerisation108 R.Mihail, S. Bittmann, F. Stoenescu, and P. Corlateanu, Rev. Chim. Min. Ind.l o * G. Natta, I. Pasquon, and E. Giachetti, Angew. Chem., 1957, 69, 213.110 Idem, Makromol. Chem., 1957, 24, 258.111 G. Natta, P. Pino, G. Mazzanti, and P. Longi, Gazzetta, 1957, 87, 549.112 G. Natta, P. Pino, and G.Mazzanti, ibid., p. 528.113 G. Natta, P. Pino, G. Mazzanti, and P. Longi, ibid., p. 570.11* A. V. Topchiev, B. A. Krentsel, N. F. Bogomolova, and Yu. Ya. Gol’dfarb,Uoklady Akad. Nauk, S.S.S.R., 1956, 111, 121.115 G. Natta, Paper presented a t the International Meeting on Chemistry of Co-ordination Compounds, Rome, Sept. 1957.116 Chenz. Eng. News, 1957, 38, 81.Chim. (Roumania), 1957, 8, 399.To be published in Ricerca scienti$ca.* The words “ isotactic ” and “ syndiotactic ” were suggested by Natta to describepolymer molecules in whose backbone chain the asymmetric carbon atoms are in regu-lar steric arrangement. In isotactic molecules the steric configuration is constant (all‘‘ D ” or ‘‘ L”), and in syndiotactic molecules it alternates between each asymmetric atomand its neighbour.Polymer molecules having a completely random arrangement ofsteric configurations are called “ atactic ”62 GENERAL AND PHYSICAL CHEMISTRY.catalyst is a complex containing organometallic bonds and more than onemetal atom. The most active catalysts are those formed by the reactionbetween an alkyl of a highly electropositive metal having a small diameter,e.g., beryllium, aluminium, or lithium, and a crystalline halide of a transitionmetal of Groups IV-VI in which the metal is in a valency state less thanthe maximum, e.g., TiCl,, TiCl,, VCl,, etc. In support of this theory, soluble,crystalline complexes have been isolated from the reaction between dicyclo-pentadienyltitanium dichloride and triethylaluminium or other alkyl-alumin-ium chl~rides.ll~~-~ These compounds are of the type [C,H,] 2TiC1,A1R2Cland slowly polymerise ethylene at low temperature and pressure.When R is phenyl, i.e., when the complex is prepared from triphenyl-aluminium, phenyl end-groups can be detected in the infrared spectrumof the polyethylenes prepared. The reaction of dicyclopentadienyldiphenyl-titanium with triethylaluminium, however, gave a complex which poly-merised ethylene to a product not containing phenyl end-groups.Fromthese and similar observations, Natta concluded 115 that chains grew byinsertion of monomeric units between the aluminium-alkyl anion bonds inthe catalytic complex. It is suggested also that the insertion of mono-meric units probably proceeds through a six-membered cyclic intermediateand a similar mechanism has been suggested independently by Julia.118X-Ray investigation 115 of the compound [C5H,],TiCl2,AlEt, hasestablished the presence of chlorine bridges between aluminium and titaniumwith a Ti-Cl distance of about 2-5 and a Ti-C1-Al angle of approximately90".on these soluble crystalline titanium-aluminium complexesconfirmed that the titanium was present in the tervalent state and that theprepared complex was a poor catalyst for polymerisation of ethylene.Introduction of small amounts of oxygen into the ethylene, before it waspolymerised, made the soluble complex as efficient a catalyst as the con-ventional Ziegler catalysts made from titanium tetrachloride.It wastherefore inferred that the presence of oxygen in the monomer oxidisedsome of the tervalent titanium present in the catalyst complex, and thathigh catalytic activity in this system depended upon the presence of somequadrivalent titanium compound.It has also been suggested120 that the effective Ziegler catalyst is atitanium alkyl which may even give rise to a free-radical type of poly-merisation.121 These suggestions are supported by the isolation 122 of puretitanium alkyls of the type RTiC1, and R,R2TiC12.The alkyltitaniumchlorides are much more stable than had hitherto been predicted and canOther work117 ( a ) G. Natta, P. Pino, G. Mazzanti, U. Giannini, E. Mantica, and M. Peraldo,J . Polymer Sci., 1957, 26, 120; (b) idem, Chimica e Industria, 1957, 39, 19; ( c ) G.Natta,U. Giannini, G. Mazzanti, and P. Pino, Angew. Chem., 1957, 69, 686; (d) idem, J.Amer. Chern. SOC., 1957, 79, 2975.11s M. Julia, Compt. rend., 1957, 245, 70.119 D. S. Breslow and N. R. Newburg, J . Anaer. Chem. SOC., 1957, 79, 5072.lZo (a) C. 0. Ncnitescu, C. Huch, A. Huch, N. Dumitrescu, and M. Gavat, Rev.Chim. hlin. I n d . China. (Roumania), 1957, 8, 395; Chem. Abs., 1957, 51, 17230; (b)C. D. Nenitescu, C. Huch, and A. Huch, Angew. Chem., 1956, 68, 438.121 H. N. Friedlander and K. Oita, I n d . Eng. Cheun., 1957, 49, 1885.122 Belgian Pat. No. 553477, Farbwerke HoechstKINETICS OF CHEMICAL CHANGE. 63be used to catalyse the polymerisation of ethylene at room temperatureand pre~sure.1~3 Polymerisation does not begin however until some of thealkyltitanium chloride has decomposed (presumably to form TiCl, and analkyl radical) or until small quantities of TiCl, are added to the reactionmixture.The polymerisations were carried out in aliphatic hydrocarbonsand it seems likely that the effective catalyst is a complex between thealkyltitanium chloride and crystalline titanium trichloride. Studies on theAlfin catalyst system,l% which also produces crystalline poly-a-olefins,confirm Natta’s conclusion that a solid phase is necessary for the formationof is0 t actic polystyrene.Investigation of the properties of isotactic polymers 125, 126 and linearpolyethylenes 1279 128 in solution by light scattering, osmotic pressure, andviscometric techniques shows clearly that, in solution, there is no significantdifference between atactic and isotactic polymers.Thus the intrinsicviscosity-molecular weight relations for atactic and isotactic polymers areessentially the same, although in the case of polystyrene the second virialcoefficient was found to vary for the two types of p 0 1 y m e r . l ~ ~ ~ ~ ~ ~ Similarconclusions have been drawn from a study of the changes of density withoutchange of phase which occur in solutions of some poly-(n-a-olefin~).~~1The preparations and properties of some propene polymers containingblock units of isotactic and atactic structures, Le., “ stereoblock ” copolymers,have been described 132 and the copolymerisation of ethylene with othera-olefins, with use of Ziegler-type catalysts, has been inve~tigated.1~3~ 134Radiation Chemistry.-Two annual reviews have been publishedcovering most aspects of this subject, and specialised reviews on the effectsof irradiation on solids,3 ionising radiation and polymer chemistry,4 thepreparation of organic compounds by radiation chemistry and the poly-merisation of unsaturated compounds by y-rays.The yield for the X- and y-ray induced oxidation of ferrousions in acid aqueous solution (Fricke dosimeter) has been determined 7 forradiations of various energies. The G values [number of ferric ions producedper 100 ev absorbed] were: 60 kvp X-rays, 13.1; 100 kvp X-rays, 14.7;l23 Belgian Pat.No. 553475, Farbwerke Hoechst.124 S. L. R. Williams, J . Van Den Berghe, K. R. Dunham, and W.J . Dulmage,lZ5 F. Ang, J . Polymer Sci., 1957, 25, 126.126 G. Natta, F. Danusso, and G. Moraglio, Makromol. Chem., 1956, 20, 37.lZ7 H. S. Kaufman and E. K. Walsh, J . Polymer Sci., 1957, 26, 124.lZ8 L. H. Tung, ibid., 1957, 24, 333.F. Danusso and G. Moraglio, ibid., p. 161.130 F. Ang and H. Mark, Monatsh., 1957, 88, 427.131 G. Natta, F. Danusso, and G. Moraglio, J . Polymer Sci., 1957, 25, 119.132 G. Natta, G. Mazzanti, G. Crespi, and G. Moraglio, Chimica e Industria, 1957,133 G. Natta, G. Mazzanti, A. Valvassori, and G. Pajaro, ibid., p. 733.134 G. Mazzanti, A. Valvassori, and G. Pajaro, ibid., pp. 743, 825.Dosimetry.J . Amer. Chem. Soc., 1957, 79, 1716.39, 275.W. M. Garrison, Ann. Rev. Phys. Chem., 1957, 8, 129.Ann. Reports, 1956, 53, 35.M.Daniels and J. Weiss, Research, 1957, 10, 341, 396.F. S. Dainton, J . Oil Colour Chemists’ Assoc., 1957, 40, 830.G. 0. Schenk, Angew. Chem., 1957, 69, 579.M. LszAr, R. Rado, and N. Kliman, Chem. Zvesti, 1957, 11, 230.J . L. Haybittle, R. D. Saunders, and A. J . Swallow, J . Chew. Phys., 1056,25, 131 364 GENERAL AND PHYSICAL CREMISTRY.220 kvp X-rays, 15.0; 30 Mev X-rays, 16.3; 6oCo y-rays, 15.5. The Gvalues for this system have also been determined as 14.9 0.8 for 250 kvpX-rays and 14.0 0.8 for 50 kvp X-rays, rather less than the value15.6 & 0.4 for 6oCo y-rays. The G values were found to be 15.6 and 15.7for electrons of energies 6.3 and 16 Mev respectively. The G value for theoxidation of air-saturated 3 x 10-3~~-ferrous ammonium sulphate in 0 .8 ~ -sulphuric acid by 4 Mev electrons has bzen determined 10 as 14.3.The radiation-induced oxidation of ferrous ion in air-saturated 0.4~-hydrochloric acid differs l1 from that in sulphuric acid in that the productionof ferric ions is not linear with dose. The initial G value, 15.8, falls withincreasing dose. The G values12 for oxidation of 0.0OlM-ferrous ion areapproximately 10.3 and 8-0 for high-energy deuterons and helium ionsrespectively. The values l3 were 4.22 and 5.69 for ionising radiation fromthe (n,a) reactions on boron and lithium respectively, in aerated solution,and the estimated value for the 2.7 Mev triton recoil was 6.7.The sensitivity of the ferrous sulphate dosimeter has been increased 14by estimating ferric iron with thiocyanate, and it has been shown that theG value is constant for X-rays in the range 0-5-2.3 A.The addition ofbenzene or cyclohexane to the ferrous sulphate dosimeter system leads 15 toa non-linear calibration. A neutron-insensitive y-ray dosimeter depends 16on the production of acid in stabilised chloroform or tetrachloroethylene.Solutions of dithizone in organic solvents show1' colour changes onirradiation with y-rays for doses as low as 100 rads, but various complicationsrender them unsuitable for dosimetry.Diffusion-controlled chemical reactions in particletracks have been studied,l8 and the theory was applied to the radiolysis ofwater. The quantity of hydrogen peroxide produced in acid solutiondepends l9 in a complicated manner on the pH, a result interpreted in termsof reactions involving the dissociation of hydrogen peroxide and HO,.and *OH.The yields of hydrogen peroxide obtained by irradiating air-free aqueoussolutions of acrylamide with X-rays have been found20 to depend on theinitial concentration of acrylamide. The results are consistent with theview that acrylamide can react with the hydrogen atoms and hydroxylradicals which would otherwise induce the reaction between the '' molecular "hydrogen and hydrogen peroxide produced. The radiolysis of aeratedsulphuric acid solutions with y-rays leads 21 to the formation of peroxymono-and peroxydi-sulphuric acid. The latter is thought to arise from theAqueous solutions.* M. H. Back and N. Miller, Nature, 1957, 179, 321.9 J.Zsula, A. Luizzi, and J. S. Laughlin, Radiation Res., 1957, 6, 661.1 0 J. P. Keene, ibid., p. 424.11 H. A. Schwarz, J . Amer. Chevrz. Sac., 1957, 79, 534.12 R. H. Schuler and A. 0. Allen, ibid., p. 1666.1:) R. H. Schuler and N. F. Barr, zbid., 1956, 78, 5756.14 S. Rosinger, 2. phys. Chem. (Frankfurt), 1957, 10, 310.1 5 C . Vermeil, Anm. Chim. (France), 1956, 13, 641.16 S. C. Sigoloff, Nucleonics, 1956, 14, Oct., 54.17 J . Wilkinson and H. J . M. Fitches, Nalztve, 1957, 179, 863.1s L. Monchik, J. L. Magee, and A. H. Samuel, J . Chem. Phys., 1957, 26, 935.19 A-M. Koulkes-Pujo, Compt. rend., 1956, 243, 1865.20 B. Collinson, F. S. Dainton, and G. S. McNaughton, Trans. Faraday Soc., 1937,21 M. Daniels, J. Lyon, and J. Weiss, J., 1957, 4388.53, 357KINETICS OF CHEMICAL CHANGE.65intermediate formation of hydrogen sulphate radicals with subsequentdimerisation. The G values 22 for evolution of hydrogen from aqueous calciumnitrate solutions in a flux of fast neutrons and y-rays decrease greatly withincreasing concentration, an effect attributed to the reaction NO,- + H _tNO, + OH-. The y-irradiation 23 of alkaline solutions of potassiumchloride leads to the liberation of free chlorine in solutions saturated withair or oxygen, the yield of chlorine being directly proportional to the energyabsorption over the range 2 x 1017-1 x 10l8 ev/ml.In the decomposition of sodium azide in solution in liquid ammonia oraqueous mercuric chloride, by irradiation with X-rays, the azide ionsdecompose 24 mainly to nitrogen molecules and electrons.Johnson and Weiss25 found that the reduction of ceric salts in diluteaqueous solutions showed initial values of G(CeIII) = 3.15 0.10 and2-45 0.08 for 200 kv X-rays and 6oCo y-rays respectively, both in thepresence and absence of oxygen.The second of the above values wasconfirmed by Whittaker 2G who obtained 2-36 &- 0.12. The radiolysis ofcerous ion-ceric ion-formic acid-sulphuric acid mixtures gave results 27interpreted by the assumption that cerous ion, formic acid, and sulphuricacid compete for reaction with hydroxyl radicals. The kinetics of the self-reduction (as a consequence of a-particle emission) of ainericium(v) andamericium(v1) in perchloric acid solution have been studied.28 Americium(v)gave only americium(m), the kinetics indicating that the reaction can beattributed to reducing species produced by a-particle bombardment of thewater.Americium(v1) gave americium(v) and finally americium(II1).Plutonium(v1) in sulphuric acid solution irradiated with y-rays is reduced 29only as far as plutonium(1v). ?-Irradiation causes oxidation 30 of aeratedferrocyanide to ferricyanide in solutions of pH less than 11, with G valuesThe irradiation with X-rays of aqueous solutions of methylene-blue withan excess of a second organic solute has been studied.31 The methylene-bluecan be reduced by hydrogem atoms and also by radicals produced from theadded organic compounds. In the presence of glucose, in a nitrogenatmosphere, reduction occurs on y-irradiation 32 (G = 5.2) but oxida-tion sensitised by ferric ion occurs with G == 7.8 equiv.for the yieldof oxidised dye and 8.2 equiv. for the yield of ferrous ion. In a stronglyacid solution containing ethanol a semiquinone free radical is produced.33The irradiation 34 with X-rays of aqueous methylene-blue solutions contain-ing ethanol, benzoate, or lactate showed, in oxygen-free solution, a reversibleup to 7.5.22 R. G. Sowden, J . Amer. Chem. SOC., 1957, 79, 1263.23 A. M. Kabakchi, Zhur. jiz. Khiin., 1956, 30, 1906.24 H. G. Heal, Tvans. Faraday SOC., 1957, 53, 210.25 G. R. A. Johnson and J. Weiss, PYOC. Roy. SOC., 1957, A , 240, 189.4 6 B. Whittaker, Nature, 1957, 180, 1302.2 7 T. J. Sworski, Radiation Res., 1957, 6, 645.28 G.R. Hall and T. R. Markin, J . Inorg. Nucleav Chein., 1957, 4, 296.29 M. Pa&, C. Ferradini, and M. Haissinsky, Gompt. rend., 1967, 245, 1138.30 X. Tarrago, E. Masri, and M. Lefort, ibid., 1957, 244, 343.31 E. Hayow, G. Scholes, and J. Weiss, J., 1957, 301.32 A. I. Chernova, V. D. Orekhov, and &I. A. Proskurnin, Zhzir.jz. Khinz., 1956,30,1343.33 A. J. Swallow, J., 1957, 1553.34 M. J. Day and G. Stein, Radiation Res., 1957, 6, 666.REP.-VOL. LTV c66 C E N E RAT, AN 1) 2'1171 SIC A J, CHlShl I STRY.reduction attributed to the reducing action of free radicals produced fromthe added solutes.Gases. The tritium p-ray-induced exchange between deuterium gas andwater vapour containing tritiated water has been investigated 35 to measurethe yields of radical-pairs (G = 11.7) and amount of water decomposed inirradiated water vapour.Exchange takes place by a chain mechanismabove 150". Exchange of deuterium between deuterium oxide and dissolvedhydrogen, under irradiation with y-rays, has been studied 36 by mass spectro-metry. The reaction rate conforms to the exponential exchange law.Work on the decomposition of carbon dioxide by ionising radiation hascontinued37 with the use of the gas under pressures of 1-50 atm. and theliquid, and irradiation from a pile or fission fragments. The basic mechanismpreviously described3* was confirmed. G values for the decomposition ofcarbon dioxide ranged from 0-005 to 8-5. The decomposition of ammoniainduced by a-particles has been studied39 as a function of pressure andintensity, and the extent of gas-phase and wall reactions estimated.Thedecomposition of nitric oxide by fission fragments40 shows an overall Gvalue of 9.5 at lo7 rads/min. and 13.8 at lo8 rads/min., leading to a cal-culated value for the primary decomposition of 3.45. The irradiation ofmethane with 2 Mev electrons leads 41 to the formation of hydrogen, ethane,propane, butane, and ethylene with G values of 5.7,2-1 , 0.14,0-04, and0.05 res-pectively. The addition of benzene vapour to acetylene retards its polymer-isation 42 when irradiated with at-particles. The mean energy necessary toproduce an ion-pair when a-particles are absorbed in binary mixtures ofacetylene, methane, or benzene with other gases has been determined.43Liquids.The r61e of ion-molecule reactions in liquid-phase radiationchemistry has been discussed.@ The effects of tracks in the radiolysis ofliquids have been discussed theoretically in terms of the distribution of freeradicals.45The exchange between chlorine and carbon tetrachloride under the in-fluence of y-rays has been studied 46 by use of a radiochlorine tracer. Tworeactions were observed : the exchange of chlorine with carbon tetrachloride,and the decomposition of carbon tetrachloride to form hexachloroethaneand chlorine. y-Ray irradiation of mixtures of butyl vinyl ether and carbontetrachloride produces 47 an equimolecular addition product. The radiolysisof various alkyl iodides by y-rays has been studied 4 8 9 4 9 under varyingconditions of temperature, phase, dose rate, and oxygen concentration, and35 R.F. Firestone, J. Amer. Chem. SOC., 1957, 79, 5593.36 J . Bardwell and P. J . Dyne, Canad. J. Chem., 1957, 35, 82.37 P. Harteck and S. Dondes, J. Chem. Phys., 1957, 26, 1727.38 Idem, ibid., 1955, 23, 902.39 B. P. Burtt and A. 33. Zahlan, ibid., 1957, 26, 846.4 0 P. Harteck and S . Dondes, ibid., 1957, 27, 546.4 1 F. W. Lampe, J. Amer. Chern. SOC., 1957, 79, 1055.42 S. C. Lind and P. S. Rudolph, J. Chem. Phys., 1957, 26, 1768.43 H. J. Moe, T. E. Bortner, and G. S. Hurst, J. Phys. Chem., 1957, 61, 422.44 R. H. Schuler, J : Chem. Phys., 1957, 26, 425.45 A. Chapiro, Radzatzon Res., 1967, 6, 11.46 J. W. Schulte, J. Amer. Chem. SOC., 1957, 79, 4643.4 7 T.S. Nikitina and Kh. S. Bagdasaryan, Z h u r . 3 ~ . Khinz., 1957, 31, 704.48 E. 0. Hornig and J . E. Willard, J. Amer. Chem. SOC., 1957, 79, 2429.4 9 R. J . Hanrahan and J . E. Willard, ibid., p. 2434KINETICS OF CHBMIC.4L CHANGE. 67the results have been interpreted theoretically. The reaction of bromo-trichloromethane with alkenes under the influence of y-rays has beenstudied.50 The irradiation of a solution of acridine in alcohol with y-raysor ultraviolet radiation leads 51 to the formation of a dimer, but if bromo-trichloromethane or carbon tetrachloride is used as solvent acridine and9-methylacridine give 52 yellow insoluble products which are the correspond-ing acridinium salts of general formula Acridine,CCl,X (X = a halogen).G values for evolution of hydrogen during the radiolysis 53 of cyclohexane-benzene mixtures by y-rays have been measured with varying concentrationsof added iodine.G values for products formed in the irradiation of C, toC, rn-paraffins have been deter~nined.~~ Hexane gave hydrogen, methane,ethylene, ethane, propenes, butanes and also C, to C,, and dimeric alkanes,and unsaturated c6 hydrocarbons. The irradiation 55 of rneopentane withhigh-energy electrons leads to the formation of hydrogen, methane, andc2-c6 hydrocarbons, but n-butane gives 56 mainly mixtures of octenes andoctanes, together with some hydrogen, ethane, butene, and C,,, CI6, andCZO hydrocarbons. isoButane gives the above and also methane, propene,and large amounts of C, hydrocarbons attributed to reactions involving C,fragments.A comparison of radiolyses with 800 kev electrons and 6OCoy-rays of n-hexane has been made 57 with the use of gas-liquid partitionchromatography. C,-C,, hydrocarbons and C,, (dimer) products werefound. The polymerisation of liquid isobutene at low temperatures inducedwith electrons and y-rays has been explained 58 in terms of a mechanisminvolving carbonium ions.Irradiation of aqueous solutions of ethylene containing oxygen withX - or y-rays gave 59 hydrogen peroxide, acetaldehyde, formaldehyde,glycollaldehyde, and an unidentified organic hydroperoxide, but oxygen-freeethylene solutions gave acetaldehyde, butyraldehyde, and apparently apolyethylene. Acetylene-oxygen solutions gave mainly glyoxal.They-ray irradiation of aqueous benzene gave results 60 indicating a short chainreaction. The radiolysis by y-rays of four different deuterated ethanols hasbeen studied.61 The G values for production of hydrogen and deuterium,and the relative proportions of these two isotopes, were measured and it wasconcluded that the primary process leading to hydrogen production wasCH,*CH2*OH + CH,*cHOH + He.MeOD has been decomposed 62 by irradiation with y-rays and the5O E. A. Heiba and L. C. Anderson, J . Amev. Chewz. SOC., 1957, 79, 4940.51 A. Kellmann, J . Chim. phys., 1957, 54, 468.52 N. Ivanoff and F. Walch, ibid., p. 473.53 M. Burton, J. Chang, S. Lipsky, and M. P. Reddy, J. Cheiia. Phys., 1957, 26, 1337.54 W. H. T. Davison, Chem. and Ind., 1957, 662.56 F.W. Lampe, J . Phys. Chem., 1957, 61, 1015.56 V. J. Keenan, R. M. Lincoln, R. L. Rogers, and H. Burwasser, J . Anzer. Ch~t1.2. Soc.,5 7 H. A. Dewhurst and E. H. Winslow, J . Chem. Phys., 1957, 26, 969.58 W. H. T. Davison, S. H. Pinner, and R. Worrall, Chem. and Ind., 1957, 1274.59 P. G. Clay, G. R. A. Johnson, and J. Weiss, Proc. Chem. SOC., 1957, 96.6o P. V. Phung and M. Burton, Radiation Res., 1957, 7, 199.6L J. G. Burr, J . Amer. Chem. SOC., 1957, 79, 751.6s G. Meshitsuka, K. Ouchi, K. Hirota, and G. Kusumoto, J . Chem. SOC. Japatt,1967, 79, 5125.1987, 78, 12968 GENERAL .4ND PHYSICAL CHEMISTRY.concentration of deuterium in the liberated hydrogen determined. Themechanism of the initial stage of the decomposition has been discussed.The action of X-rays 63 on aerated aqueous ethanol gives only acetaldehyde,but in deaerated solution butane-2 : 3-diol is also produced.The ir-radiation 64 of acetic acid-oxygen solutions with 40 Mev helium ions leads tothe formation of glycollic, glyoxylic, and oxalic acids, formaldehyde, andcarbon dioxide. The electron irradiation of tri-n-butyl phosphate gives 65di-n-butyl hydrogen phosphate (G = 1-5) , n-butyl dihydrogen phosphate(G = 0.17), and gases. The y-ray induced decomposition of aqueoustetranitromethane gives 66 trinitromethane (G = 3.73). The radiolysis ofmixtures of organic liquids in the presence of diphenylpicrylhydrazyl hasbeen studied.67Solids. The y-ray induced decomposition of various solid nitrates hasbeen investigated.68 The principal products were nitrite and oxygen, theyield of the former being linear with the dose.The G values for the overalldecomposition of various solid nitrates by X-rays, corresponding to thereaction NO,- - NO,- + +02, increases 69 as the " free space " (differencebetween the volume of the crystal and the volume of the ions in it)increases. The effect 70 of electron irradiation on dianthrone and spiropyrancompounds is to produce colours similar to those produced by ultravioletirradiation.Irradiation with y-rays increases 71 the catalytic activity of alumina forthe hydrogen-deuterium exchange reaction, and of an iron oxide-potassiumcarbonate catalyst for the Fischer-Tropsch process.72Polymerisatiort . The kinetics of the polymerisation of aqueous solutionsof acrylamide initiated by X- and y-rays have been investigated 73 and theresults explained in terms of a mechanism in which termination is by mutualinteraction of growing chains, and in which the distribution of initiatingradicals is effectively uniform. The addition 74 of acidified ferric perchlorateto the above system causes linear termination of the polymerisation.Inthe y-ray induced polymerisation of acrylonitrile after-eff ects have beenobserved 75 due to the presence of long-lived free radicals.The irradiation of poly(methy1 methacrylate) solutions in L arioussolvents with y-rays 76 has been studied viscometrically and by measuringthe extent of reaction with diphenylpicrylhydrazyl. The po1,ymerisation63 G.G. Jayson, G. Scholes, and J. Weiss, J., 1957, 1358.134 W. M. Garrison, H. R. Haymond, W. Bennett, and S. Cole, J . Chem. Phys.,135 T. F. Williams, R. W. Wilkinson, and T. Rigg, Nature, 1957, 179, 540.6 6 A. Henglein and J. Jaspert, 2. phys. Chem. (Frankfurt), 1957, 12, 324.137 L. Bouby and A. Chapiro, J . Chim. phys., 1957, 54. 341.13* C. J. Hochanadel and T. W. Davis, J . Chem. Phys., 1957, 27, 333.6 9 J. Cunningham and H. G. Heal, Nature, 1957, 179, 1021.7 O Y. Hirshberg, J . Chem. Phys., 1957, 27, 758.72 R. W. Clarke and E. J. Gibson, Nature, 1957, 180, 140.'3 E. Collison, F. S. Dainton, and G. S. McNaughton, Trans. Faraday SOC., 1957,74 Idem, ibid., p. 489.7 5 R, Bensasson and A. Bernas, J . Chim. phys., 1957, 54, 479.' 6 A.Henglein, M. Roysen, and W, Schnabel, 2. phys. Chem. (FranRjurt), 1957,1956, 25, 1282.E. TY. Taylor and I€. W. Kohn, J . Amer. Chew. Soc., 1957, '99, 252.53, 476.10, 137KINETICS OF CHEMICAL CHANGE. 69has been found 77 to be slowest in benzene and more rapid in carbon tetra-chloride, chloroform, and dioxan. The radiation field for 6oCo and 137Cssources in various geometrical dispositions has been ~ a l c u l a t e d , ~ ~ and anestimate made of the yields to be expected if the sources were used to producepolymerisation.Graft copolymers have been prepared 79 by y-irradiation of polymer-monomer combinations. The block polymerisation of chlorotrifluoro-ethylene initiated by y-rays has been investigated go for doses of30-1000 rads/hr., the rate being directly related to the square root of theirradiation intensity.Theoretical discussions of the radiation-inducedchanges in polymers have been given.81382 A theoretical mechanism hasbeen suggested 83 whereby excitons formed by the irradiation of polymersmay cause cross-linking.This theory has been criticised 84 on the groundsthat the mobility of radicals may account for all the effects observed in theirradiation of polyethylene.The effects of y-ray and electron irradiation on an aqueous solution ofpoly(viny1 alcohol) ( M , 27,000400,000) have been studied 85 by use ofmeasurements of light scattering, viscosity, ultracentrifuging, and ultra-violet spectra. The observations indicated that poly(viny1 alcohol) formscross-links over the entire range of concentrations.The cross-linking and degradation of seven polyacrylates by 1000 kvpelectrons have been investigated.86 The energy dissipated for each fractureof the main chain was about 500 ev, and that for formation of each cross-linkedunit was 80-300 ev.Six different polymers were shown to be degraded 87if irradiated with X- and y-rays at low concentration, but at higher con-centrations some of them form cross-links. The effect of y-rays is to produce 88scission in poly(methy1 methacrylate) and cross-linking in polystyrene.The effects of temperature in the irradiation of polyethylene (swelling,change of sol fractions, and elasticity) have been measured 89 and the resultsinterpreted in part as clue to an increase in the number of radical-radicalreactions above the melting point.Infrared absorption measurementsindicate the formation of five- or six-membered ring systems when poly-ethylene is irradiated with y-rays. The nuclear magnetic resonancetechnique has been used Dl to study the irradiation of polyethylene with77 A. Henglein, C. Schneider, and W. Schnabel, 2. phys. Cltem. (Frankfurt), 1957,12, 339.7~ M. Magat and L. Reinisch, Internat. J . Appl. Radiation Isotopes, 1956, 1, 194.78 W. K. W. Chen, R. B. Mesrobian, D. S. Ballantine, D. J. Metz, and A. Glines,J . Polymer Sci., 1957, 23, 903.8o M. LazAr, R. Rado, and N. Kliman, Chem. Zvesti, 1956, 10, 584.81 R. W. Pearson, J . Polymer Sci., 1957, 25, 189.82 R. Simha and L. A. Wall, J . Phys. Chem., 1957, 61, 425.83 B.G. Collyns, J. F. Fowler, and J. Weiss, Chem. and Ind., 1957, 74.84 R. W. Pearson, ibid., p. 209.85 J. Berkowtich, A. Charlesby, and V. Desreux, J. P o l p e r Sci., 1957, 25, 490.8 6 A. R. Shultz and F. A. Bovey, ibid., 1956, 22, 485.s7 P. Alexander and A. Charlesby, ibid., 1957, 23, 355.s 8 L. A. Wall and D. W. Brown, J . Phys. Chem., 1957, 61, 129.8 s A. Charlesby and W. H. T. Davison, Chem. and Ind., 1957, 232.91 S. Fujiwara, A. Amainiya, and K. Shinohara, J . Chem. Phys., 1957, 26, 1343.Irradiation ofpolymers.M. Dole, D. C. Milner, a-cl T. F. Williams, J . Amer. Chem. SOC., 1957, 79, 480970 GENEKAL AND PHYSICAL CHEMISTKY.dcuterons, and also with neutrons plus y-rays. The melting behaviour ofpolyethylene after y-ray and pile irradiations has been studied.93Smoked sheet rubber, previously oriented in the calendering process, hasbeen 94 cross-linked by exposure to 2 Mev electrons in the absence of vulcan-ising agents, and subsequently showed anisotropic elastic properties.Thevulcanisation 95 of natural and synthetic rubbers by X-rays increases theelastic moduli.The irradiation of many com-pounds in this category has been studied in order to help in elucidating thecomplicated problems encountered in radiation biology.The electron and X-ray irradiation of glucose solutions 96 produces un-identified substances with characteristic absorption spectra. The ir-radiation 97 of several y-lactones leads to the formation of the correspondingascorbic acids. Thiourea 98 gives mainly free sulphur with a high G value,indicating a chain reaction.Cholesterol has been bombarded with 30 kev 14C positive ions.99 Theproducts containing radiocarbon included tram-dehydroandrosterone, carbondioxide, carbon monoxide, formaldehyde, formic acid, and oxalic acid.Asimilar experiment loo with sodium benzoate gave benzoic acid, carbonmonoxide, oxalic acid, and di-m-carboxyphenylmethane. If 14C-labelledcholesterol is stored in air, the @-particle emission leads Io1 to oxidation aboutthe 5 : 6-double bond.The self-irradiation of [35S]~~-methionine by the @-radiation gives lo2 upto twelve decomposition products detected by radiography of a chromato-gram. The X-ray irradiation of tyrosine lo3 gives 3 : 4-dihydroxyphenyl-alanine which then gives an indole derivative.Possibly the changes are thesame as those occurring during the metabolic oxidation of tyrosine to amelanin pigment. Cysteine is oxidised lO4 to a disulphoxide.The irradiation of solutions of proteins and various amino-acids leads lo5to increased optical absorption at short wavelengths (except for cystine).Gelatine gives an insoluble gel, possibly owing to cross-linking. It wasconcluded that irradiation results in rupture of carbon-carbon bonds andhydroxylation of aromatic rings.The irradiation of aqueous solutions of deoxyribonucleic acid with X-raysleads 106 to a decrease in viscosity attributed to scission of phosphate bonds.Compounds of biochemical importance.Material stored in vacuo remained unchanged.92 N.Fuschillo and J. A. Sauer, J . Chenz. Hhys., 1957, 26, 1348.93 M. Dole and W. H. Howard, J . Phys. Chem., 1957, 61, 137.94 A. Charlesby and E. von Arnim, J . Polymer Sci., 1957, 25, 151.95 A. S. Kuzminskii, T. S. Nikitina, and V. L. Karpov, Atomic Energy (U.S.S.R.),9 6 C. T. Bothner-By and E. A. Balazs, Radiation Res., 1957, 6, 302.s 7 B. Coleby, Chem. and Ind., 1957, 111.gs W. M. Dale and J. V. Davies, Radiation Res., 1957, 7, 35.gg B. Aliprandi and F. Cacace, Ann. Chim. (Italy), 1956, 46, 1204.B. Aliprandi, F. Cacace, and G. Giacomello, Ricerca sci., 1956, 26, 3029.W. G. Dauben and P. H. Payot, J . Amer. Chenz. Soc., 1956, 78, 5657.102 J. KolouSek, J. Liebster, and A. Babickf, Nature, 1957, 179, 521.J. Nosworthy and C. B.Allsopp, J . Colloid Sci., 1956, 11, 565.I o 4 R. BrdiClra and 2. Spurny, Cltenz. Listy, 1967, 51, 1267.105 RI. A. Khenokli and Y e . M. Lapinskaya, Boklady Ahad. Nauk S.S.S.K., L Y Wlo6 M. Daniels, G. Scholes, J . Weiss, and C. M. Wheeler, J . , 1957, 226.English translation, 19.56, 1, No. 3, 137; Publ. in J . Nuclear Energy, 19.57, 4, 268.110, 125KINETICS OF CHEMICAL CHANGE. 71The radiolysis of glycerophosphates has been st~died.1~7 Aqueous co-carboxylase (thiamine pyrophosphate) and thiamine show lo8 a decrease ofoptical density probably owing to attack on the chromophores by freeradicals. Hyaluronic acid depolymerises lo9 and some glucosamine isproduced. Cellulose and pectin irradiated with y-rays are degraded withloss in viscosity, both immediately and also owing to an after-effect.Ifnearly dry oxygen-free cellulose is used after-effects may be initiated ll1subsequently by admitting oxygen and terminated by the presence of water.Viscometric measurements on pectin solutions indicate 112 that irradiationcauses degradation, and that added sucrose, glucose and fructose have aprotective effect .C. F. H. T.L. H. S.A. L.F. D. S. B.THERMOCHEMISTRY.THIS Report is divided according to the main activities of thermochemistry :(i) the measurement of heats of reaction, usually divisible into (a) com-bustions, (b) reactions other than combustion; and (ii) the evaluation ofthe quantities needed to adjust heats of reaction so determined to refereither to standard-state reactions (for which all the participating substancesare in their accepted standard states) OY to gas-state reactions (for whichparticipating compounds are gaseous and participating elements gaseousatoms).These quantities include heats of fusion, vaporisation, sublimation,and atomisation.Although we emphasise work published in 1957 we try to indicate themajor developments since the last report was prepared three years ago.Many references are given in a recent review.l Certain topics are omittedeither because they have been discussed recently elsewhere, such as bondenergies by Sehon and Szwarc,2 or because they concern more the widersubject of chemical thermodynamics, such as the evaluation of thermo-dynamic functions from spectroscopy and low-temperature heat capacities.Heats of adsorption and mixing are also excluded.The former requireinterpretation in terms of current models of adsorption processes and aremore relevant to surface phenomena. Although many measurementsof the latter are reported, most of them arise from growing interest in thethermodynamic interpretation of solution phenomena (the testing of lattice-model and other theories) and are not of immediate thermochemical value.The elements have been the subject of a notable book.3Heats of Combustion.-Measurements of heats of combustion provide thelo’ G. Scholes, W. Taylor, and J. Weiss, J , , 1957, 235.lo* M. Ebert and A. J. Swallow, Radiation Res., 1957, 7, 220.log A. Caputo, Nature, 1957, 179, 1133.R. E. Clegg and 2. I. Kertesz, Science, 1956, 124, 893.ll1 R.E. Clegg, Radiation Res., 1957, 6, 469.112 Z. I. Kertesz, B. H. Morgan, L. W. Tuttle, and M. I-avin, ibid., 1956, 5, 372E. F. Westrum, Ann. Rev. Phys. Clzem., 1957, 8, 1.A. H. Sehon and M. Szwarc, ibid., p. 439.D. R. Stull and G. C. Sinke, “ The Thermodynainic Properties of the Elements,”Amer. Chem. SOC., Washington, 195672 GENERA41, AND PHYSICAL CHEMISTRY.most general method of determining heats of formation, but the combustionproducts must be definable thermochemically with precision. This hasbeen relatively easy for hydrocarbons and compounds containing carbon,hydrogen, ar,d oxygen only, and in the past decade the difficulties presentedby organic compounds containing nitrogen or sulphur have been largelyo~ercome.~ Considerable progress has also been made in the reliabilityof the combustion of organic chlorine-, bromine-, and iodine-containingcompo~nds.~ Compounds containing other elements have not yet beenstudied successfully.Recently, however, noteworthy advances have beenachieved for organic fluorine-containing and certain organometallic com-pounds (see p. 73); this progress has been largely dependent upon themoving-bomb technique, the most versatile and reliable method yet devisedfor extending accurate combustion calorimetry to groups of compounds notaccessible by conventional methods.Hydrocarbons. Since the appearance of the revised edition of the,4merican Petroleum Institute Research Project 44 tables in 1954 severalsheets of new or revised data have become available; these do not call forcomment.Day and Oestrich have measured heats of combustion andderived the resonance energies of dimethyl- and diphenyl-fulvene.Compounds containkg carbon, hydrogen, and oxygen. A noteworthypaper by Coops et aL7 summarises work begun 20 years ago on the deter-mination of the absolute heat of combustion of benzoic acid. The latestvalue quoted by these authors (26,435 J/g.) is compared with their earlierone (26,438 J/g.) and with those of other workers. The agreement betweenthe various investigations is good, the total " spread " being about 0.02%.From heats of combustion Jaffe, Prosen, and Szwarc deduced values of-127.9, -148.2, and -161 kcal./mole for the heats of formation of liquidacetyl, propionyl, and butyryl peroxides, and values of -45, -54, and-60 kcal./mole for the heats of formation of the acetate, propionate, andbutyrate radicals.Briner and Dallwigk have determined the heat ofcombustion (- 1697 kcal./mole) of the ozonide of trans-stilbene and deducedits heat of formation (-102) and heat of scission (84.5 kcal./mole). Nichol-son 10 has measured the heat of combustion of acetylacetone and obtaineda value in good agreement with that calculated by Kharasch.llOrganic nitrogen-containing compomds. Heats of combustion forthirteen explosives including nitro-compounds , nitrates, and nitramines l2and thirty-six triazoles , tetrazoles , and related high-nitrogen compounds l3have been reported. Some of these compounds could not be made to burnsmoothly or completely. Heats of combustion of liquid ethyl, rc-propyl," Experimental Thermochemistry ", ed.by F. D. Rossini, Interscience, New York,J. H. Day and C. Oestrich, J . Org. Chem., 1967, 22, 214.J. Coops, N. Adriaanse, and K. van Nes, Rec. Trav. chim., 1956, 75, 237.L. Jaffe, E. J . Prosen, andM. Szwarc, J . Chern. Phys., 1957, 27, 416.E. Briner and E. Dallwigk, Helv. Chinz. Acta, 1957, 40, 1978.1956, chaps. 6 and 7.5 See ref. 4, chaps. 8, 9, and 10.l o G. R. Nicholson, J., 1957, 2431.l1 M. S. Kharasch, Bur. Stand. J . Izes., 1929, 2, 359.l2 L. Medard and M. Thomas, Me'm. Pmdres, 1957, 38, 45.13 M. M. Williams, W. S. McEwan, and R. A. Henry, J . Phys. Chem., 1957, 81, 261MACKLE : THERMOCHEMISTRY. 73and isopropyl nitrates have been determined and the corresponding heatsof formation derived.14Smith l5 has published a tableof heats of combustion of twenty organic iodine compounds.These arebased, after small corrections, upon unpublished work by K. J. Karlsson.16Good, Scott, and Waddington17 have continued their study of thecombustion of organic fluorine compounds and established the generalreliability of their method. They report heats of combustion and formationfor six compounds selected to include volatile liquids, non-volatile solids,a group of isomers, and compounds with a wide range of fluorine content,namely o-, m- , and p-fluorobenzoic acids, fluorobenzene , benzotrifluoride ,and polytetrafluoroethylene : p-fluorobenzoic acid is suggested as a referencesubstance for the intercomparison among different laboratories of bomb-calorimetric data for fluorine compounds. Neugebauer and Margrave l8have determined the heats of combustion and formation of 1 : l-difluoro-ethylene with a conventional bomb calorimeter.Organometallic compounds.In an important paper on the heat ofcombustion of tetraethyl-lead Scott , Good, and Waddington l9 haveillustrated the power of the method of rotating-bomb calorimetry whenapplied to a problem involving hitherto intractable chemical, equilibration,and correction difficulties. The complex mixture of Pb, PbO, Pb,O,,PbO,, and other lead compounds produced by the combustion was convertedquantitatively into Pb2+ ion in solution by 2~-nitric acid containing a littlearsenious acid.The relatively large volume of final solution was quicklyrendered homogeneous and in equilibrium with the gas phase by rotatingthe bomb. Fairbrother and Skinner 2o have measured the heat of com-bustion and deduced the heat of formation of diphenylmercury ; theirresults differ significantly from earlier onesJ21 but are supported by indepen-dent heat of reaction data.,,In the combustion of trimethyl-arsine Long and Sackman 23 experienced difficulties of incomplete com-bustion and oxidation similar to those encountered with trimethyl-bismuthand -antimony.% The reliability of their values for the heats of combustionand formation depends, therefore, upon accurate analysis of the combustionproducts, which they claim to have achieved.More recently 25 they reporteddata for trimethylphosphine, and discussed the values derived for themean dissociation energies of the P-C, As-C, Sb-C, and Bi-C bonds. AOrganic halogen-containing compounds.Miscellaneous organic compounds.l4 D. M. Fairbrother, H. A. Skinner, and F. W. Evans, Trans. Faraday SOC., 1957,l5 L. Smith, Acta Chem. Scand., 1956, 10, 884.l8 K. J. Karlsson, Thesis, Lund, 1941.l7 W. D. Good, D. W. Scott, and G. Waddington, J . Phys. Chern., 1956, 60, 1080.la D. W. Scott, W. D. Good, and G. Waddington, J . Phys. Chem., 1956, 60, 1090.2o D. M. Fairbrother and H. A. Skinner, Trans. Faraday Soc., 1956, 52, 956.21 A. S. Carson, E. M. Carson, and B. R. Wilmshurst, Nature, 1952. 170, 320.22 C. L. Chernick, 13.A. Skinner, and I. Wadso, Trans. Faraday Soc., 1956, 52, 1088,23 L. H. Long and J. F. Sackman, ibid., p. 1201.Z4 Idem, ibid.. 1954, 50, 1177; 1955, 51, 1062.25 Idem, ibid., 1957, 53, 1606.53, 779.C. A. Neugebauer and J. L. Margrave, J . Phys. Chem., 1956, 60, 1318; J . Amer.Chem. SOC., 1957, 79, 133074 GENERAL AND PHYSICAL CHEMISTRY.notable gap is the continued lack of precise information on the heats ofcombustion and formation of the parent of the series, trimethylamine.Clarke and Datta 26 have reported values for the heats of combustion ofglycerol 1-(disodium phosphate), glycerol 2-(disodium phosphate), andglucose l-(disodium phosphate). These cannot, however, be accepted asvery reliable, mainly because of the absence of any serious attempt toanalyse the combustion products.Handrick 27 has described yet anothermethod for doing this: it involves the principle of the summation of group,as distinct from bond, energies.A practical feature is the claim that itcan predict explosive properties. A treatment, similar in principle butrather simpler, has been devised by Young et aL28 for organic nitrogencompounds and appears to give fairly reliable results.Inorganic substances. Accurate measurements of the heats of com-bustion of pure calcium, dysprosium, ytterbium, erbium, holmium, andyttrium 29 are reported. For calcium it was necessary to work a t 50 atm.pressure, as otherwise the amount of unburnt metal was quite large. Theremaining metals were readily burnt at the usual oxygen pressure of 25 atm.The heats of formation of the oxides formed have been deduced. Fischeret aL30 measured the heats of combustion of chromium, molybdenum,tungsten, and nickel carbonyls.The results, when combined with knownthermochemical data, give reliable estimates of the heats of formation ofthe solid carbonyls. The paper on nickel carbonyl reports an interestinginternal firing technique for volatile liquids. Mah 31 has reported valuesof -400.5, -178.2, and -140.6 kcal./mole respectively for the heats offormation of alumina, molybdenum trioxide, and molybdenum dioxide.These are all in good agreement with those of earlier workers.Reactions other than Combustion.-Despite their great thermochemicalvalue, the use of combustion reactions is often precluded. For instance,the chemistry of most combustions involving compounds containingphosphorus, boron, silicon, arsenic, or metals needs much clarificationand control before the heat changes associated with them can be reliablydetermined. Fortunately there are a variety of other reaction types whichcan be used to provide precise thermochemical data for such com-pounds, including hydrogenation and reduction, halogenation, hydrolysis,and miscellaneous reactions.Most noteworthy among therecent contributions to the calorimetry of gas-phase hydrogenation arethose of Lacher and his co-workers32 who have obtained highly reliableCalculation of heats of combustion.Heats of hydrogenation and reduction.26 H.B. Clarke and S. P. Datta, Biochem.J., 1957, 66, 451.2 7 G. K. Handrick, Ind. Eng. Chem., 1956, 48, 1366.28 J. A. Young, J. E. Keith, P. Stehle, W. C. Dzombak, and H. Hunt, ibid., p. 1375.29 E. J. Huber, E. L. Head, and C. E. Holley, J . Phys. Chern., 1956, 60, 498, 1457,30 A. K. Fischer, F. A. Cotton, and G. Wilkinson, J . Amer. Chem. Soc., 1956, 78,31 A. D. Mah, J . Phys. Chem., 1957, 61, 1572.32 J. R. Lacher, E. Emery, E. Bohmfalk, and J . D. Yark, ./. Phys. Chem., 1956, 60,492; J. R. Lacher, A. Kianpour, and J. D. Park, 1454; J. R. Lacher, A. Kianpour,P. Montgomery, H. Knedler, and J. D. Park, 1957,61, 1125; J. R. Lacher, A. Kianpour,F. Oetting, and J. D. Park, Trans. Faraday SOC., 1956, 52, 1500.1582; 1957, 61, 497, 1021.6168; 1957, 79, 2044MACKLE : THERMOCHEMISTRY.75data for the heats of hydrogenation of a wide range of organic bromides,chlorides, and fluorides. A palladium-charcoal catalyst is used for thehydrogenation and the heat quantities are determined in a specially con-structed isothermal flow-calorimeter of high accuracy. The heats ofhydrogenation of CH,CI, C,H,Cl, C2H,C1, n-c3H,F, iso-C3H,F, CF,=CFCI,CF,=CHCl, CF,=CCl,, and CH,=CHBr are reported, and in several instancesthe corresponding heats of formation have been deduced. The heat offormation of hydrogen bromide from the gaseous elements has beenmeasured directly for the first time and the value obtained supports thecurrently accepted indirect value.33 In the course of this work the lowermembers of a homologous series proved more difficult to hydrogenate thanthe higher. The lower fluoro-compounds provide the extreme example inthis respect ; the hydrogenation of methyl and ethyl fluorides and perfluoro-vinyl bromide has not yet been made sufficiently quantitative to permitcalorimetry.In a series of papers Turner et ~ 1 . ~ ~ have reported the heatsof platinum oxide-catalysed hydrogenation in acetic acid solution ofbicyclo[2 : 2 : llheptene, bicyclo[Z : 2 : llheptadiene, bicyclo[2 : 2 : Sloctene,bicyclo[2 : 2 : 2]octadiene, cyclooctatetraene, some seven-membered non-benzenoid aromatic compounds, some unsaturated steroids and some cis-and tram-cycloolefins. The results illuminate a number of theoreticalquestions including the relative importance of angle strain and non-bondedrepulsions in the bicycloheptene and bicyclooctene systems ; the stabilityrelationships among olefins possessing double bonds at different positionsin a fused ring system; and the energetic interpretation of the directionalspecificity of certain enol reactions.They also indicate that there is no“ homoallylic resonance ” stabilisation in bicycloheptadiene and lead tovalues of 2.4, 0.9, 28, 13, and 28 kcal./mole for the resonance energies ofcyclooctatetraene, 1 : 3 : 5-cyclooctatriene, azulene, heptafulvene, and hepta-fulvalene respectively. Ideally, of course, resonance energies should beevaluated from gas-phase measurements and the above values are subjectto uncertainties introduced by solvation and other effects. Turner andGarner 35 measured the heats of hydrogenation in acetic acid of 1-methyl-cydohexene, methylenecyclohexane, 1-methylcyclopentene and methylene-cyclopentane and showed that the methylcycloalkenes are the more stableisomers.The effect of alkyl substituents on the heats of hydrogenation of olefinshas been commonly attributed to hyperconjugation alone.Often, however,the resulting hyperconj ugation energies have appeared rather large whencompared with the conjugation energies obtained for unsaturated substituents.This anomaly has been discussed by Taft and Kreevoy36 who point outthat hyperconjugation is not the only contributing influence. The hydro-genation of a double bond markedly decreases the intrinsic electronegativity33 “ Selected Values of Chemical Thermodynamic l’roperties,” Series 111, NationalHureau of Standards, Washington.34 R.B. Turner, W. R. Meador, and K. E. Winkler, J . Anier. Chem. SOC., 1957, 19.4116,4122; R. B. Turner, W. R. Meador, W. von E. Doering, L. H. Knox, J. R. Mayer,and D. W. Wiley, ibid., p. 4127; R. B. Turner and W. R. Meador, ibid., p. 4133.36 R. B. Turner and R. H. Garner, ibid., p. 253.36 R. W. Taft and M. M. Kreevoy. ibid., pp. 4011, 401676 GENERAL AND PHYSICAL CHEMISTRY.of its atoms, for the sp2 valence state is appreciably more electronegativethan the sp3. It is plausible, therefore, that, in addition to hyperconjugation,polar or inductive effects contribute significantly to the observed influenceof a-saturated substituents on heats and free energies of hydrogenation.Taft and Kreevoy have devised additivity equations by which the hyper-conjugation and inductive effects can be estimated separately; the relativemagnitudes of hyperconjugation and conjugation effects then appearreasonable.The average conjugation effect is about ten times the hyper-conjugation effect of an a-hydrogen atom.Flitcroft, Skinner, and Whiting 37 have designed a calorimeter speciallysuited to the measurement of heats of hydrogenation in solution. Animportant point is that the reaction vessel is mechanically shaken. Theheats of hydrogenation of hex-l-ene, fumaric acid, maleic acid, dodeca-3 : 9-diyne, dodeca-5 : 7-diyne, and octa-1 : 7-diyne are reported. A value of10 kcal./mole is deduced for the overall conjugation energy of the system-CEC-CEC-.Neugebauer and Margravela have measured the heats offormation of CF,, C,F,, and C10,F by hydrogenation and decompositionin a bomb calorimeter. Their result (151.7 kcal./mole) for C,F, agrees wellwith that of D U U S ~ ~ but differs considerably from those of von Warten-berg39 and Kirkbride and D a v i d ~ o n . ~ ~ Their result for CF4 supports thatof Scott, Good, and Waddingt~n.~l Hill and Williamson 42 have derivedthe heat of formation of potassium manganate in solution by measuringthe heat of reduction of potassium permanganate by hydrogen peroxide.Recently heats of formation of organic chloro-compounds have been derived mainly from the combustion studies ofSmith and his co-workers at Lund and the U.S. Bureau of Mines Group atBartle~ville.~~ Where comparison can be made, the results of these twoschools generally agree, but as they employ basically the same techniquesome independent check has been needed.KirkbrideU has recentlysupplied this in a valuable paper on the calorimetry of both substitutiveand additive chlorination of hydrocarbons. He has determined directlythe heats of substitutive chlorination (RH + C1, + RC1 + HC1) forbenzene, chlorobenzene , toluene, cyclohexane, .ia-hexane, ethylene dichloride ,and chloroform and derived the heats of formation of 1 : 1 : S-trichloro-ethane, chlorocyclohexane, and benzyl chloride; and the heats of additivechlorination of cis-dichloro-, trichloro-, and tetrachloro-ethylene. Thechlorinations were carried out by bubbling chlorine gas through a speciallyconstructed reaction vessel immersed in a Dickinson-type calorimeter.For substitutive chlorinations in the aromatic nucleus anhydrous ferricchloride was used as catalyst.All other chlorinations were photoactivated.Kirkbride's results confirm the reliability of modern methods of combustioncalorimetry of organic chloro-compounds. They also support the value37 T. Flitcroft, H. A. Skinner, and M. C. Whiting, Trans. Faraday SOC., 1957,53, 784.a* H. C. Duus, Ind. Eng. ChePn., 1955,47,1445.3s H. von Wartenberg, 2. anorg. Chem., 1955, 278, 326.40 F. W. Kirkbride and F. G. Davidson, Nature, 1954, 174, 79.41 D. W. Scott, W. D. Good, andG. Waddington, J . Amel.. Chem. SOC., 1955, 77, 845.42 R. A. IV.Hill and J. F. Williamson, J., 1957, 2417.43 See H. A. Skinner, Ann. Reports, 1954, 51, 36.44 F. W. Kirkbride, J . Appl. Chem., 1956, 25, 519.Heats of halogenationMAC KLB THE RMOCIl E M I STHY . 77(-30.2) quoted by Smith et ~ 1 . ~ ~ for the heat of formation of carbon tetra-chloride. This is about 3 kcal./mole lower than the value quoted in theNational Bureau of Standards Circular 500. Finally, Kirkbride's value(32 kcal./mole) for the heat of chlorination of gaseous tetrachloroethylenemay be compared with that (-30) previously estimated from e q ~ i l i b r i a . ~ ~Ito's more recent value*' appears to be seriously erroneous. Lacheret ~ 1 . ~ ~ have measured the heats of vapour-phase addition bromination oftetrafluoro- and chlorotrifluoro-ethylene with ferric bromide and antimonybromide as catalysts, and of addition chlorination of perfluorinated but-l-ene, isobutene, and pent-l-ene with ferric chloride on activated carbon ascatalyst.The data obtained, together with those previously reported,49show that the heats of bromination and chlorination of a double bond aregreatly influenced by the substituents on its carbon atoms; variations upto 20 kcal./mole occur. The same authors 50 have redetermined the heatsof hydrobromination of propene and cyclopropane and found values of20-4 and 25.8 kcal./mole respectively. The latter is about 3 kcal./molehigher than their previous value. Benson and from equilibriumstudies of the side-chain bromination of toluene, have obtained a value of-20 kcal./mole for the heat of formation of benzyl bromide; this is about 6kcal./mole greater than that derived from kinetic studies by several authors,notably Szwarc, and it is contended that certain interpretations of the kineticdata have been oversimplified. Szwarc has replied to these criticisms.Skinner and his co-workers 52 have measured the heats of reaction ofbromine vapour with liquid tetramethyltin and of bromine and iodine withhexamethylditin and derived values of -41-4 & 11, -28.2 & 11, and-23.3 5 22 kcal./mole respectively for the heats of formation of gaseous(CH,),SnBr, (CH,),SnI, and (CH,),Sn2.The large error limits are due to anuncertainty of *lo kcal./mole in the only available value for the heat offormation of tetramethyltin.This uncertainty is due mainly to incompletecombustion of the metal alkyl. The heat of formation of titanium tetra-bromide has been derived independently by two groups 53 from the heatof bromination of titanium. Gross, Hayman, and Levi 53 have also revisedtheir earlier value for the heat of formation of titanium tetrachloride andreported a value for the heat of formation of zirconium tetrachloride.%Hydrolyses usually proceed cleanly and quantita-tively and are frequently used in thermochemistry. Sunner and Wadso 55have measured the heat of hydrolysis and deduced the heat of formation45 L. Smith, L. Bjellerup, S. Krook,and H. Westermark, Acta Chenz. Scand., 1953,7,65.413 K. J. Ivin and F. S. Dainton, Trans. Faraday Soc., 1947, 43, 32.47 J.Ito, Univ. Colorado Stadies, 1954, 29, 83,4 8 J. R. Lacher, L. Caseli, and J. D. Park, J . Phys. Chem., 1956, 60, 608; J. R.Lacher, A. Kianpour, and J. D. Park, ibid., 1957, 61, 584.4 0 J. R. Lacher, J. J. McKinley, C. M. Snow, L. Michel, G. Nelson, and J. D. Park,J . Amer. Chenz. Soc., 1949, 71, 1330; J. R. Lacher, J, J. McKinley, C. Walden, K. Lea,and J. D. Park, ibid., p. 1334.5 0 J. R. Lacher, A. Kianpour, and J. D. Park, J . Phys. Chem., 1957, 61, 1124.5L S. W. Benson and J. H. Buss, J . Phys. Ghem., 1957, 61, 104.53 J . B. Pedley, H. A. Skinner, and C. L.Chernick, Trans. Faraday Soc., 1957,53,1612.53 H. L. Schlafer and H. H. Smidtke, 2. phys. Chem. (Frankfurt), 1957, 11, 297;54 I d e m , ibid., p. 1285.55 S. Sunner and I, Wadso, ibid., p.455.Heats of hydrozysis.P. Cross, C. Hayman, and D. L. Levi, Trans. Faraday Soc., 1957, 53, 160178 GENE K A 1, il N L) PI3 YSI CA 1, C l i IS M I STKY.of thiolacetic acid. Their value for the latter (-52.3) may be comparedwith that (-51.5 kcal./mole) derived from heats of comb~stion.~6 Hearneand White 57 have measured the heat of solution of uranium tetrachloridein aqueous hydrochloric acid-lithium chloride mixtures at constant ionicstrength. The observed variation of this quantity with the hydrochloricacid concentration conflicts with current views on the hydrolysis of theuranium(1v) ion. The authors conclude that any attempt to derive heatsof hydrolysis from heats of solution is liable to be seriously misleadingunless adequate data are available from which the effect of the medium onthe heats of solvation of the ions can be evaluated.Flitcroft and Skinner 58have measured the heats of hydrolysis of ethyl orthosilicate and chloro-triethylsiloxane and derived the corresponding heats of formation. Theheat of the gaseous redistribution reaction between ethyl orthosilicate andsilicon tetrachloride to form chlorotriethoxysilane is estimated to be 4.3kcal./mole. Other thermochemical data derived from heats of hydrolysisinclude the heats of formation of Na202, NaO,, and K02,59 nitramide,60and cyanuric chloride.6l The last result leads to a new value for the heatof trimerisation of cyanogen chloride. The heats of hydrolysis of adenosinetriphosphate 62 and hydroxylamine hydrochloride 63 have also been reported;the former is a reaction of great importance in biological energy transfers.Heats of miscellaneous reactions. Considerable attention has beengiven recently to the energetics of formation of complexes and co-ordinationcompounds.As part of an extended investigation of steric effects in dis-placement reactions Brown and Gintis measured the heats of reaction ofgaseous trimethylboron and diborane with pyridine bases in nitrobenzenesolution. The calorimetric system described is of general interest in thatit is specially suited to work where one reactant is gaseous and the otherliquid. From the difference in the heats of reaction of trimethylboronwith the 4- and the 2-alkylpyridines it can be inferred that a steric strainof about 6 kcal./mole exists in 2-picoline, thus supporting the predictionby Brown et aE.65 of strains of this magnitude for all homomorphs of o-tert.-butyltoluene.Brown and Holmes 66 claim to have shown, contrary tosuperficial expectation, that the relative strengths of the boron halides asLewis acids decrease in the order BBr, > BCI, > BF,. Their conclusionsare based on measurement of the heats of formation of the 1 : 1 molecularcomplexes of the boron halides with pyridine and nitrobenzene. It appearsthat resonance contributions play a dominant r81e in determining therelative acceptor properties of the boron halides. McCoy and Bauer 6756 S. Sunner, Ada Chem. Scand., 1955, 9, 847.5 7 J. A..Hearne and A. G. White, J., 1957, 2081.5* T.Flitcroft and H. A. Skinner, J., 1956, 3355.6s P. W. Gilles and J . L. Margrave, J . Phys. Chew$., 1956, 60, 1333.60 J. D. Ray and R. A. Ogg, ibid., p. 1460.62 R. J. Podolsky and M. F. Marales, J. BZoZ. Chern., 1956, 218, 946.63 S. S. Muhammad, D. H. Rao, and M. A. Haleem, J. Indian Chern. Suc., 1957,34,101.84 H. C. Brown and D. Gintis, J. Amer. Chern. SOC., 1956, 78, 5378, 5384.H. C. Brown, G. K. Barbaras, H. L. Berneis, W. H. Bomer, R B. Johannesen,H. C. Brown and R. R. Holmes, ibid., 1956, 78, 3173-A. R. Humphries and G. R. Nicholson, J., 1957, 2429.M. Grayson, and K. L. Nelson, ibid., 1953, 75, 1.s7 R. E. McCoy and S . H. Bauez, ibid., p. 2061~r.ux~x : THBKMOCHEMISTRY. 79have estimated the bridge-breaking energy of diborane based on the heatsof reaction of (i) trimethylboron with ammonia and the methylamines, (ii)diborane with the methylamines, and (iii) tetramethyldiborane with tri-methylamine.Their value, 28 3: 2 kcal./mole, is subject to certainassumptions. The heats and entropies of combination of various alkaline-earth ions with the ligand anions of ethylenediaminetetra-acetic acid,nitrilotriacetic acid, etc., have been derived by Martel 68 from cell measure-ments of dissociation constants. These studies supplement earlier ones 69and the most significant general feature of the accumulated data is that thestabilities of the chelate compounds are due almost entirely to a favourableentropy increase, the enthalpy changes being relatively unimportant.These general conclusions are supported by direct calorimetry by Charles 70and by Care and S t a ~ e l e y , ~ ~ but the detailed results of the latter workersthrow doubt on the overall reliability of the AH values obtained by Martel'smethod.The energies and entropies of the molecular association of amidesin benzene have been reported by Davies and Thomas.72 The hydrogen-bridge energy is found to be 3.6 kcal./mole in all cases. From optical-density estimations of equilibrium constants at different temperaturesBier 73 has estimated the heats of complex-formation of s-trinitrobenzenewith a series of aromatic hydrocarbons and aromatic amines. These liewithin the range 0.45 to 3 kcal./mole and depend, as might be expected,upon the degree of electron-donating substitution of the benzene ring.Thermodynamic studies of solutions of iodine in solvents with which itforms molecular complexes have been reported by Jepson and Rowlinson. 74The heats of solution calculated from solubility-temperature measurementsagree well with those determined directly.75 The complex-forming powerof the various solvents appears to increase in the following order : paraffins <halogenobenzenes < benzene < mesitylene < ethyl bromide < ethylether < pyridine < ethyl iodide. Chernick et aZ.76 have measured theheats of addition of rhombic sulphur to triethyl phosphite and tri-n-propyl-and tri-n-butyl-phosphine, and deduced values for the dissociation energiesof the thiophosphoryl bonds, S=PR,. If*the value chosen by the authorsfor AH&,) is correct, these all lie close to 91 kcal./mole.The nature of Rappears to have no appreciable effect on D(S=PR,). Compounds in whichphosphorus, arsenic, or antimony forms a direct donor-acceptor bond togallium afford another means of studying the interplay of several factorson bond strength. The energies involved in the molecular addition reactionsbetween GaCl, and POCl, and GaC1, and PCl, have been measured recentlyby Greenwood et al.; 77 this work necessitated the design of an all-glass68 A. E. Martel, Rec. Trav. chinz., 1956, 75, 781.6 8 F. F. Carini and A. E. Martel, J . dmer. Chenz. Sor., 1952, 74, 5745; 1953, 75,7 0 R. G. Charles, ibid., p. 5854.73 M. Davies and D. K. Thomas, J . Phys. Chem., 1956, 80, 763, 767.73 A.Bier, Rec. Trav. chirn., 1956, 75, 866.74 W. B. Jepson and J. S. Rowlinson, J . , 1956, 1279.7 5 K. Hartley and H. A. Skinner, Trans. Faraday SOC., 1950, 46, 621.7 6 C. L. Chernick, J . B. Pedley, and H. A. Skinner, J., 1957, 1851.7 7 N. N. Greenwood and P. G. Perkins, J . Inorg. Nuclear Chewz., 1957,. 4, 291;4810; 1954, 76, 2153.R. A. Care and L. A. K. Staveley, J . , 1956, 4571.N. N. Greenwood, P. G. Perkins, and K. Wade, J . , 1957, 434580 GENERAL AND PHYSICAL CHEMISTRY.precision calorimeter suitable for work with hygroscopic or reactive sub-stances in an inert atmosphere. The small value (3.4 kcal./mole) for theheat of the reaction between GaCl, and PCl, implies that the complexCl,Ga+PCl, is not very stable. The gas-phase heat of formation of theGaCl,,POCl, complex is 22.6 kcal./mole.This gives some indication ofthe Cl+Ga bond strength.Other thermochemical studies reported include the thermal decom-position of silane at 680" in a flow cal~rimeter,~~ the results of which supportthe lower values for the heat of formation of silane; the heat of the gas-phase reaction between dinitrogen pentoxide and nitric oxide, leading to avalue of -3 kcal./mole for the heat of formation of gaseous dinitrogenpentoxide; 79 the heats of a number of semiacetalisation reactions;the dissociation energy of indium phosphide; the heats of reaction withdilute hydrochloric acid of Sr3P2, Li,Bi, Ba,Bi,, BaBi, Li,As, Mg,As,, andZn,As, from which are deduced values of -160, -39, -128, -40, -81,-96, and -30 kcal./mole respectively for the heats of formation of thesecompounds; 8, the estimation from electron-impact studies of the heat offormation of the C2H radical and the energies of the C'C and C-H bonds inacetylene and of several bonds in substituted acetylenes; 83 the heats of for-mation of the aqueous oxide ions of americium, AmO,+(aq) and Am0,2+(aq),from microcalorimetric measurements ; the heat of formation of aluminiumnitride by direct nitridation in a bomb calorimeter ; 85 the heats of formationof NaA10, and LiA10,; 86 and the ortho- and meta-silicates of barium andstrontium, dibarium trisilicate, and barium di~ilicate.~~ Muldrow andHepler s8 have determined the heats of solution in water or dilute aqueousperchloric acid of K2Cr207, K,CrO,, and (NH,),Cr,O, and the heats ofreaction of K,Cr,O, and CrO, with aqueous alkali and of K2Cr0, withaqueous acid.From the results the heats of formation of K,CrG,, K2Cr,07,(NH,),Cr,O,, (Cr0,2-) (as) and (Cr207,-) (aq) are derived. With theexception of the value for ammonium dichromate these heats of formationappear more reliable than any previously published. The value (-425)for (NH4),Cr20, may be contrasted with that (-429) recently reported byNeugebauer and Margrave s9 and with that (-430 kcal./mole) derivedfrom heats of combusti~n.~~ It is, however, based on a value of -138for the heat of formation of CrO,, whereas Neugebauer and Margrave 897 8 E. 0. Brimm and H. H. Humphreys, J . Phys. Chem., 1957, 61, 829.7 B J.D. Ray and R. A. Ogg, ibid., p. 1084.M. Bakes, Compt. rend., 1957, 244, 2726.K. Weiser, J . Phys. Chem., 1957, 61, 513.82 S. A. Shchukarev, M. P. Morozova, and Kho-yn Kan, Zhur. obshchei Khirn., 1957,27, 289; S. A. Shchukarev, M. P. Morozova, Kho-yn Kan, and V. T. Sharov, ibid., p.290; S. A. Shchukarev, M. P. Morozova, Kho-yn Kan, Tszi-Tao Kuan, and E. Vol'f,ibid., p. 293.8a F. H. Coats and R. C. Anderson, J . Amer. Chem. SOC., 1957, 79, 1340.84 S. R. Gunn and B. B. Cunningham, ibid., p. 1563.85 C. A. Neugebauer and J. L. Margrave, see ref. 18.8 6 J. P. Coughlin, J . Amer. Chenz. SOC., 1957, 79, 2397.87 R. Baranay, E. G. King, and S. S. Todd, ibid., p. 3639.88 C. N. Muldrow and L. G. Hepler, ibid., p. 4045.so A. F. Kapustinski, A.A. Shidlovskii, Izvest. Sekt. Platiny i Drug. Blagorod MetalInst. Obshchei i Neorg., Akad. Nauk S.S.S.R., 1956, 30, 31,C. A. Neugebauer and J. L. Margrave, J . Phys. Chem., 1957, 61, 1429MACBLE : TIIERMOCHERIISTRY. S lassert that the correct value for the latter is -142 kcal./mole. Price andTrotman-Dickenson,gl from studies of the rate of pyrolysis of (CH,) 2Hg,(CH,) ,Cd, and (CH,),Zn, have deduced values for the bond-dissociationenergies, D(CH,-MCH,) and D(CH3-M-) where M is Hg, Cd, and Zn. Theseare 50 and 7 for the compounds of mercury, 46 and 21 for those of cadmiumand 47 and 35 kcal./mole for those of zinc. Dainton and his co-workers 92used an isothermal fusion calorimeter to measure the heats of copoly-merisation of sulphur dioxide with certain olefins..These correlate wellwith the corresponding heats of hydrogenation except for cyclopentenewhich has the lowest heat of hydrogenation but the highest heat of copoly-merisation; this discrepancy is discussed. The present results point to avalue of about 81 kcal./mole for the sum of the two carbon-sulphur bonddissociation energies in polysulphones ; other data indicate that the corre-sponding quantity in dimethyl sulphone is 80 kcal./mole. The heats offormation of twenty-six substances, mainly ureas and diphenylamines,have been reported.g3 Goton and Whalley 94 have critically reviewedliterature data for various thermodynamic properties of benzoic acid.They recommend a value of -380,140 -& 290 abs. joules mole-1 for theheat of formation at 2 5 " ~ .A most important development in alloythermochemistry was the introduction of the method of tin-solutioncalorimetry by Ticknor and Bever 95 which has proved capable of providingfar more accurate data on the heats of formation of solid binary alloys thanhad hitherto been possible. During the past three years it has been notablyexploited by Kleppa 96 and Kleppa and Kaplan 96 who reported the heatsof formation of the following alloys : tin-rich binary and ternary alloys, liquidalloys of copper, liquid mercury-indium alloys, and solid alloys of gold withcadmium, indium, tin, and antimony.Heats of Fusion, Vaporisation, Sublimation, and Atomisation.-Among themost intractable problems of chemistry during the last few decades havebeen those of obtaining unambiguous values for the heats of dissociationof nitrogen and carbon monoxide and the heat of sublimation of carbon.Various authors at different times have recommended widely differentvalues for these q~antities.~' In the past two or three years, however,more evidence in support of the higher values has acc~mulated.~~ Byelectron-impact studies with use of essentially monoenergetic electronsBurns 99 and Clarke loo have arrived at a value of 9.65 ev for D(N,) andtheir work has been confirmed by Frost and McDowell.lO1 By a similar91 S.J. W. Price and A. F. Trotman-Dickenson, Tvans. Favaday Soc., 1957, 53,939, 1208.92 F. S. Dainton, J. Diaper, K. J . Ivin, and D. R. Sheard, ibid., p. 1269.93 P. Tavernier and M.Lamouroux, Mdm. Poudres, 1957, 38, 65.94 R. Goton and E. Whalley, Canad. J . Chern., 1956, 34, 1506.85 L. B. Ticknor and M. B. Bever, J . Mefals, 1952, 4, 941.9 6 0. J. Kleppa. J . Phys. Chem., 1955, 59, 175, 354; 1956, 60, 446, 842, 846, 852,858; 0. J. Kleppa and M. Kaplan, ibid., 1957, 61, 1120.97 See refs. 2 and 43.g8 L. Brewer and A. W. Searcy, Ann. Rev. Phys. Chem., 1956, 7, 259.J. F. Burns, J . Chew. Phys.. 1955, 23, 1347.loo E. M. Clarke, Canad. J . Phys., 1954, 32, 764.l o 1 D. C. Frost and C , A. McDowell, Proc. Roy. SOC., 1956, A , 236, 278.The thermochemistry of alloysmethod, Lagergrenlo2 has concluded that 11.1 ev is the correct value forD(C-0) and this is supported by Brackett's work.lo3 In a most importantpaper Chupka and Inghram,lo4 using a mass spectrometer, have determinedthe composition of carbon vapour in equilibrium with carbon in a Knudsencell at 2500" K.The vapour consists mainly of C(g), C,(g), and C,(g) andthe calculated heats of sublimation of these species are 171, 190, and 200kcal./mole respectively. Thus the high value of around 170 kcal./mole forthe heat of sublimation of monatomic carbon seems established. It issupported by the high D(C-0) value already discussed, by the total vapour-pressure measurements of several workers,lo5 by the mass-spectroscopicLangmuir-type experiments of Honig,lo6 and by the more recent evaporation-and effusion-rate experiments of Thorn and Wins10w.l~~ A review on thedetermination of the latent heat of carbon L(C) has been published byKern.lo8 The following values are now generally accepted: D(N,) = 9-76 ev(225.04 &- 0.1 kcal./mole); D(C0) = 11.09 ev (25576 0.43 kcal./mole);L(C) = 170.89 & 0.5 kcal./mole.The value of the effusion cell-mass spectrometer method is well illustratedby its contribution to the solution of the problem of the latent heat ofsublimation of carbon, but this is only one important example of its power.Since it was developed five years ago, the method has been applied withconspicuous success to the elucidation of the chemical composition andtemperature-pressure behaviour of many vapours at high temperatures,notably of inorganic oxides.The entire subject was reviewed some timeago by Brewer and S e a r ~ y . ~ ~ Since then the method has been applied tothe determination of the heats of sublimation of boron and boric oxide,lo9the gaseous oxides of zirconium, tungsten, and titanium,l1° and severalmetals of low volatility.111Using a saturated vapour method, Allen 112 has determined the heat ofsublimation of chromous iodide.The value (71.4 kcal./mole), when com-bined with known values for the heat of formation of CrI,(c) and the heatsof atomisation of chromium and iodine, gives a value of 55.7 kcal./molefor the Cr-I average bond energy. The heats of vaporisation of the followingsubstances have been derived from vapour-pressure studies: 2 : 3 : 3-tri-chlor~heptafluorobutane,~~~ cobalt nitrosyl carbonyl,ll* acetone,l15 andl o 2 C. R. Lagergren, Diss. Abs.. 1956, 16, 770.lo3 T.E. Brackett, J. Phys. Chem., 1956, 24, 1103.lo* W. A. Chupka and M. G. Inghram, ibid., 1955, 59, 100.Io5 M. Hoch, P. E. Blackburn, D. P. Dingledy, and H. L. Johnston, ibid., p. 97;K. J . Thorn and G. H. Winslow, J . Chew. Phys., 1955, 23, 1369; P. Goldfinger, MLm.SOC. roy. sci. Lizge, 1955, 15, 341.Io8 R. E. Honig, J. Chern. Phys., 1954, 22, 126.lo' K. J . Thorn and G. H. Winslow, ibid., 1957, 26, 1S6.lo6 D. M. Kern, J. Chem. Educ., 1956, 33, 272.lo9 A. W. Searcy and E. Myers, J. Phys. Chem., 1957, 61, 957.J. Berkowitz, W. A. Chupka, and M. C. Inghram, -1. Chem. Phys., 1967,26, 1207;1957, 27, 85; J . Phys. Chem.. 1957, 61, 1569.111 R. G. Johnston, D. E. Hudson, W. C. Caldwell, F. 11. Spedding, and M'. R.Savage, J. Chern. Phys., 1956, 25, 917.112 T.L. Allen, J. Anzer. Chern. Soc., 1956, 78, 5476.113 R. H. Capps and W. M. Jackson, J. Phys. Chew., 1956, 60, 811.114 B. Mohai and G. Bor, Naturwiss., 1957, 44, 325.115 R. A. Pennington and K. A. Dobe, J . Amel.. Chew. SOC., 1957, 79, 805NELSON DIELECTRIC MEASUREMEN?'S. 83n- and iso-propyl and wand iso-butyl nitrate ; 116 and from vapour-flow calori-metry: 1 : 1 : 2-trichloroethane, propan-1-01, and propan-2-01.117Petit et aZ.118 have measured the heats of fusion of KF, LiF, CaF,, SrF,,and BaF, by high-temperature cryometry and those of the alkali boratesand molybdates by using a thermal diagram method. Kemp et aZ.119 havereported cryoscopic heat of fusion and vaporisation data for a series ofaliphatic di- and tri-nitroxy-compounds.Waddington's group at theU.S. Bureau of Mines have reported comprehensive investigations of thethermodynamic properties of a number of compounds of key importanceto the petroleum industry.120 Among the experimental methods employedwere those of flow and low-temperature calorimetry and comparativeebulliometry. The results, in conjunction with previously or currentlydetermined heats of combustion , yield thermodynamic data, includingheats of formation of the vapours and liquids, and heats of fusion andvaporisation. The compounds studied include thiophenol, butane-l-thiol,methyl-n-propylamine, ethanethiol, dimethylamine , fluorobenzene , cyclo-heptane, cyclooctane, 1 : 3 : 5-cycZoheptatrieneJ and a series of l-olefins.Li 121 has summarised data on the heats of vaporisation and fusion of pyr-idine. Bondi and Simkin have discussed the hydrogen-bond contributionto the heats of vaporisation of aliphatic alcohols.From data in theliterature, Papini and Cuomo 123 calculated the heat of vaporisation ofethyl alcohol from 0" to 200" c. Marcus 124 has devised formulae by whichthe energies and entropies of vaporisation of liquids and metals may beestimated.H. M.DIELECTRIC MEASUREMENTS.SINCE Debye's formulation of the theory of the electrical polarisation ofmatter, by far the most important application of dielectric measurementshas been to evaluate dipole moments. Although dipole-moment studiescontinue valuable in the field of molecular structure, a rapidly growinginterest in the wider subject of dielectric relaxation is now evident and thisReport is confined to it.However, for molecular polarisabilities and dipole116 P. Gray and M. W. Pratt, J., 1957, 2163.11' K. D. Williams and R. H. Harrison, J . Chem. Phys., 1957, 26, 1049.11* G. Petit and A. Crbmieu, Compt. rend., 1956, 243, 360; G. Petit and M. Jaeger,llg M. D. Kemp, S. Goldhagen, and F. A. Zihlman, J . Phys. Chem., 1957, 61, 240.l20 D. W. Scott, J. P. McCullough, W. D. Good, J. F. Messerly, R. E. Pennington,T. C. Kincheloe, I. A. Hossenlopp, D. R. Douslin, and C,. Waddington, J . Amer. Chem.Soc., 1956, 78, 5457; D. W. Scott, J. P. McCullough, W. N. Hubbard, J. F. Messerly,I. A. Hossenlopp, F. R. Frow, and G. Waddington, ibid., p. 5463; H. L. Finke, D. W.Scott, M.E. Gross, J. F. Messerly, and G. Waddington, ibid., p. 5467; J. P. McCullough,W. N. Hubbard, F. R. Frow, I. A. Hossenlopp, and G. Waddington, ibid., 1957, 79, 561;D. W. Scott, H. L. Finke, J. P. McCullough, J. F. Messerly, R. E. Pennington, I. A.Hossenlopp, and G. Waddington, ibid., p. 1062; J. P. McCullough, H. L. Finke, M. EGross, J. F. Messerly, and G. Waddington, J . Phys. Chem., 1957, 61, 289.ibid., 1957, 244, 1734, 1900.Ie1 K. Li, J . Phys. Chem., 1957, 61, 782.14t A. Bondi and D. J. Simkin, J . Chem. Phys,, 1956, 25, 1073.las G. Papini and S. Cuomo, Antincindio, 1956, 8, 338.gZ4 R. J. Marcus, J . Chem. Phys., 1957, 26, 176584 GENERAL AND PHYSICAL CXEMISTRY.moments we mention the books by Smith and Smyth and the review bySutton which have appeared since these topics were last reported; we omitalso more specialised fields of ferro-electrics and dielectric saturation andbreakdown.The period reviewed is confined to 1955-1957, except wherea topic has not been reviewed before.General Theory of Relaxation Phenomena.-Several important reviewshave appeared. One by Bottcher emphasises the molecular interpretation.An excellent summary of dielectric absorption in solids and liquids is givenby Dryden and Meakin~.~ Smyth’s book is the most comprehensivetreatise on dielectric behaviour available.Further attempts torefine Debye’s expression 6 relating the relaxation time of a molecule to itsmolecular dimensions and the inner friction of the medium have been made.While often yielding the correct order of magnitude for the size of therelaxing molecule, the Debye equation (in which the macroscopic viscosityis commonly used in place of the inaccessible coefficient of inner friction) issometimes conspicuously inadequate , especially for spherical molecules inmedia of widely differing macroscopic viscosities.Hill divides polar liquidsinto two classes according to whether or not the rotation of the dipoles is pre-vented by freezing. For liquids which lose all orientational freedom on solidi-fication, an equation similar to Debye’s is offered to describe the variation ofrelaxation time with viscosity ( 7 ) . Debye’s “ molecular radius ” is replacedby the mean radius of gyration ( K ) of the molecule about any axis normalto the dipole axis :Relaxation time, viscosity, and molecular dimensions.Satisfactory agreement with experiment for a number of organic liquids withrigid structure is reported from the use of this equation, which includesPowles’s expression relating the macroscopic relaxation time (T*) to themicroscopic, or molecular, relaxation time (T).isthe dielectric constant at zero frequency and elco that a t high frequencies. Theprimes (’) and seconds (”) are used to denote the real and imaginary parts,respectively, of the complex dielectric constant.No simple dependence of T* on 7 is to be expected for liquids which retainorientational freedom on solidification, but Fairweather lo has suggestedthat, analogously to macroscopic turbulence, the energy loss should beV is the molar volume,1 J .W. Smith, ‘‘ Electric Dipole Moments,” Butterworths Scientific Publications,2 C. P. Smyth, “ Dielectric Behaviour and Structure,” McGraw-Hill Book Co., Inc.,L. E. Sutton, ‘ I Determination of Organic Structures by Physical Methods,” ed.C. J. F. Bottcher, Chew. WeekbEad, 1956, 52, 460.5 J. S. Drydy and R. J. Meakins, Rev. Pure Afipl. Chem. (Australia), 1957, 7, 15.P. Debye,R. S. Holland, G. N. Roberts, and C. P. Smyth, J . Amer. Chew. Soc., 1956, 78, 20. * N. E. Hill, Proc. Roy. Soc., 1957, A , 240, 101.J. G. Powles, J . Chem. Phys., 1953, 21, 633.lo A. Fairweather, Pioc. Phys. Soc., 1955, 68, B, 1038London, 1955.New York, 1955.Braude and Nachod, Academic Press Inc., New York, 1955, ch. 9.Polar Molecules,” Chemical Catalog Co., New York, 1929, ch.VNELSON DIELECTRIC iblvlEASUKEhlEN?’S. 85related to density rather than viscosity when T* is small, -q being the dominantfactor with processes of long T*. This approach was tested quantitativelyin the microwave region for dilute solutions of benzophenone in benzene andcarbon tetrachloride at different temperatures ; results in fair agreement withtheory are claimed, although the experimental results may be in errorowing to the unusual form of the tan &frequency curves. Emphasising theinadequacy of taking a sphere as a model for all molecules, and following theearlier ideas of Perrin l1 and Fischer,l2 Le F h r e and his co-workers l3 intro-duced the use of “ shape factors ”. They sought a correlation between T*of a standard molecule (nitrobenzene) in various solvents and certainproperties of the solvent. It was noticed that T* was more linearly relatedto the product of q of the solvent and some measure of the anisotropy of thesolvent, than to y1 itself. Two empirical equations were developed whichpermit an a priori calculation of T* from the polarisability ellipsoids of thesolute molecules and the viscosities, depolarisation factors, and dielectricconstants of the solvents.The absence of a close correspondence between T* and y1 for both solutionsand pure liquids is sometimes attributable to special effects, such as non-rigidity or molecular association.For example, intermolecular hydrogen-bonding may be responsible l4 for the substantially larger T* of py-rrolidinethan of pyrrole which has the larger 3.In fact, Aihara and Davies l5 usedsuch departures to assess the degree of non-rigidity of certain molecules, acondition for detecting non-rigidity being that T* should be less than thatexpected for a rigid structure. Many substituted benzene, aniline, alicyclic,and oxalic acid derivatives were studied and qualitative estimates of rigiditymade in most cases. Similar arguments were used to account for the shortrelaxation times of solutions of diphenyl ether and certain cychhexanederivatives.16 A more detailed high-frequency study in decalin solution ofthree hydroxy-compounds in which the hydroxyl groups are protected bybulky radicals, thus hindering formation of hydrogen-bonds, shows theexistence of two distinct absorption regions.1’ The lower-frequency absorp-tion was attributed to rotation of the molecule as a whole and the higher oneto independent rotation of the hydroxyl group about the carbon-oxygenbond.Both processes have similar activation energies (2.8-3-1 kcal./mole),the larger frequency factor of the latter giving rise to the higher frequencyof absorption. Dipole-moment components along the axes and at rightangles to the axes of the molecules, calculated from bond moments, agreedwell with values calculated from the experimental data by use of Onsager’sequation, thus supporting the interpretation of the absorptions. The rigidmolecule, o-dichlorobenzene, in contrast, showed a single relaxation time,though Poleyls has suggested that a second dispersion for such moleculesl1 F.Perrin, J . Phys. Radium, 1934, 5, 497.l2 E. Fischer, 2. Physik, 1949, 12’9, 49.l 3 J. Y. H. Chau, R. J. W. Le Fkvre, and J. Tardif, J . , 1967, 2293.l4 R. S. Holland, Diss. Abs., 1966, 16, 34.l5 A. Aihara and M. Davies, J . Colloid Sci., 1356, 11, 671.l6 F. Dieringer, 2. Physik, 1956, 145, 184.l7 M. Davies and R. J. Meakins, J . Chem. Phys., 1957, 26, 1584.18 J. P. Poley, AppL Sci. Res., 1955, 4(5), 33786 GENERAL AND PHYSICAL CHEMISTRY.may exist at even higher frequencies, because of the discrepancy betweenemf and n2. Indeed, a small rise in d f at f > 1O1O c./sec. was observed forlarge molecules such as nitrobenzene. A molecular resonance mechanismhas been suggested for this absorption.lgDistribution of relaxation times.A useful summary and critical dis-cussion 2o of the various ways of analysing and representing dielectric datahas been given. The equations of Fuoss and Kirkwood 21 and of Cole andCole 22 for symmetrical and that of Davidson and Cole 23 for unsymmetricaldispersions having a distribution of relaxation times are the most satisfactory.Poley's 24 suggestion that the asymmetry of dispersion observed for poly-hydroxy-compounds 23 arises from a superposition of several relaxationeffects fails to make the data fit. Other examples of viscous polar liquidswhere Davidson and Cole's skewed-arc representation applies best have beenThat the asymmetry cannot be due to long-range interactionthrough hydrogen bonds has been pointed out by Denny25 who observedasymmetric dispersions for alkyl halides at low temperatures.An interestingcase has been reported by Winslow et al. for solutions of tolyl xylyl sulphonein supercooled o-terphenyl, where the distribution of relaxation times de-creased with dilution.26 Clearly, dipole-dipole interaction cannot be thedominant factor here and it is thought that the condition for Debye behaviour,namely, that the period of the applied field should be large compared withthe average time between inelastic collisions, is not fulfilled. A theoreticaltreatment 27 for spherical molecules in a crystalline field shows that thepresence of barriers of different magnitude between equilibrium orientationsmay produce a discrete set of relaxation times, the maxima of dielectric lossfrequently being asymmetrical.Hydrogen-Bonded Systems.-Multiple dispersion has been found forseveral short-chain alkyl alcohols.28 The principal absorption, characterisedby a single relaxation time, is believed to involve partial breaking and re-forming of intermolecular hydrogen bonds to permit reorientation ofhydroxyl groups, while the high-frequency dispersion, described by a rangeof relaxation times, arises from orientation of the alkyl group with respectto the H-O-H plane.The latter process, being less specifically co-operative,is the faster. Smyth and his co-workers 29 prefer these mechanisms to theearlier views of Brot et aZ.30 that the dispersions are due to quasi-crystallinecomplexes and free molecules, respectively.Values of E,' in excess of n2l9 J. P. Poley, J . Chem. Phys., 1955, 23. 405.2O R. H. Cole, ibid., p. 493.21 R. M. Fuossand J . G. Kirkwood, J . Amer. Chenz. Soc., 1941, 63, 385.22 K. S . Cole and R. H. Cole, J . Chem. Phys., 1941, 9, 341.2s D. W. Davidson and R. H. Cole, ibid., 1961, 19, 1484.24 J. P. Poley, Physicu, 1953, 19, 300.25 D. J. Denny, J . Chem. Phys.. 1957, 27, 259.26 J. W. Winslow, R. J. Good, and P. E. Berghausen, ibid., p. 309.2 7 J. D. Hoffman and B. Axilrod, J . Res. Nut. Bur. Stand., 1955, 54, 357; J. a.Hoffman, J . Chem. Phys., 1955, 23, 1331.28 F. X. Hassion and R. H. Cole, ibid., p. 1756; W. Dannhauser and K. H. ('ole,ibid., p. 1762; D. J. Denny and R. H.Cole, ibid., I>. 1767.z 9 G. B. Rathmann, A. J. Curtis, P. L. McGeer, and C. Y. Smyth, J . Anier. Ckem.Soc., 1956, 78, 2035.30 C. Brot, M. Magat, and L. Reinisch, Kolloid Z., 1953, 134, 101NELSON : DIELECTRIC; MEASUREMENTS. 87suggest a third dispersion a t higher frequencies; this has been observed byBrot31 Empirical values of Kirkwood’s 32 correlation factor g were cal-culated and their temperature-dependences analysed in terms of associationequilibria of the type (ROH),* (ROH),+,.28 The onset of local struc-ture, leading ultimately to glass formation, appears to be responsible for thecurvature of the plot of log T* against 1/T plots a t low temperatures. As-sociation in poly(ethy1ene glycols) 33 and in solutions of o-cresol and eugenol 34has been studied at microwave frequencies, and intramolecular hydrogen-bonding identified as the origin of the radio-frequency absorption in certainsubstituted o-phen~ls.~~Recent work36 on the dielectricrelaxation process in ice supports B jerrum’s lattice-defect mechanism.37Imperfections of two types were assumed : (i) orientational defects producedby the rotation of a water molecule around one of its four bonds in thehexagonal lattice, and (ii) ionised states where a proton moves to a neighbour-ing molecule forming H30+ and OH- ions.For both cases the possibleproton jumps were treated statistically and the theory was extended tomixed hydrogen fluoride-ice crystals. The results showed that the protontransfer at H30+ ions is the dominant mechanism at the lower concentrationsof hydrogen fluoride and for high concentrations the orientational-defectprocess is the more important.36 Riehl 38 has assessed the activation energyfor ion-pair formation (8-9 kcal./mole) and for orientation (12-13 kcal./mole). On the basis of the greatly reduced relaxation times and lowactivation energies (ca.4 kcal./mole) for solid solutions of ammoniumfluoride in ice, Zaromb and Brill 39 have suggested that ions might generatefault sites which are propagated over large distances in the lattice; it wascalculated that the rotation of as many as 2-5 x lo4 water molecules isaffected by 0.002% of ammonium fluoride.*ORecent measurements indicate that the dispersion for pure water is moreconsistent with a narrow spectrum of relaxation times than a singleIt is surprising that the Debye equation should be so well obeyed for water,a system where marked deviations might be expected.Grant,42 however,has shown that a similar equation can be derived by starting from the morerealistic model of the structure of the liquid due to Haggis et aZ.43 Whilethis model adequately explains the decrease in relaxation time observed fordilute ionic solutions in terms of an increasing number of broken hydrogenIce, water, and aqueous ionic solutions.31 C . Brot, Arch. sci. (Geneva), 1956, 9, Spec. No., 49.32 J. G. Kirkwood, J . Chem. Phys., 1939, 7, 175.33 N. Koizumi and T. Hanai, J . Phys. Cherut., 1956, 60, 1496; N. Koizumj, J . Client.34 E. Fischer and N. Zengin, Z.Physik, 1957, 147, 113.35 R. J. Meakins, Trans. Faraday Soc., 1955, 51, 371.36 H. Granicher, C. Jaccard, P. Scherrer, and A. Steinemann, Discuss. I;araday Soc.,1967, 23, 50; Helv. Phys. Acta, 1955, 28, 300.37 N. Bjerrum, Kgl. danske Videnskab. Selskab, Mat-fys. Medd., 1951, 27, No. 1.38 N. Riehl, Zhur. $2. Khim., 1955, 29, 1372.39 S. Zaromb and R. Brill, J . Chpm. Phys., 1956, 24, 896.* O S. Zaromb, ibid., p. 1110.r1 E. H. Grant, T. J. Buchanan, and H. F. Cook, ibid., 1957, 26, 156.dl E. H. Grant, ibid., p. 1575.43 G. H. Haggis, J. B. Hasted, and T. J. Buchanan, ibid., 1952, 20, 1452.Phys., 1957, 27, 62588 GENERAL AND PHYSICA4L CHEMISTRY.bonds, it fails to account for effects at high concentrations where the trendis reversed. These observations were interpreted in terms of hydration ofions by Harris and O’Konski and discussed in relation to various types ofion-solven t interaction .uPhase Transitions and Orientation Freedom in Solids.-Smyth has col-lected and summarised most of the available data up to 1953, and gives over100 references.The review by Dryden and Meakins also is fairly com-prehensive. Molecular shape has been correlated with orientational freedomin solid phases for tetrahalogenomethanes 45 where the condition for freedomof rotation is that the van der Waals radii along the carbon-halogen axesshould differ by no more than 9%. For molecules of more irregular shape,rotation of segments or groups within the molecule may be the cause ofabsorption, as observed for certain solid triglycerides,46 camphor deriv-atives:’ and liydroxy-compounds.4s The parallelism between relaxationtime, activation energy, and frequency factor on the one hand, and chain-length on the other, has confirmed that the low-frequency absorption inlong-chain aliphatic esters and ethers arises from a rotation of the moleculeas a whole about the long axis.49 The need for the presence of lattice im-perfections has been suggested.49, 50 No explanation of the microwavedispersion in these compounds has yet been established, though Harper andO’Dwyer’s model,51 based on free rotation of the dipoles, is consistent withthe data for long-chain methyl esters.52 Cole and his collaborators havestudied the changes in dielectric behaviour accompanying the order-disordertransitions in solid hydrogen and deuterium halides 53 and hydrogen sul-phide.54 The experimental results were discussed in relation to possiblestructures of the various phases; dipole interactions alone do not adequatelyaccount for the observed results and the need for an extension of the measure-ments to higher frequencies (>1 Mc./sec.) has been stressed.The low-temperature phases showed multiple dispersion, suggesting that anisotropymay be important, as in solid methanol and CH,0D.55 The staticdielectric constants for the high-temperature phases in both the halides andthe sulphide were in reasonable agreement with values calculated from gasdipole moments by Onsager’s equation, thus indicating the absence ofsignificant co-operative effects from orientation.Phase transitions insodium ~almitate,~G thiocy~lohexane,~~ long-chain t h i ~ l s , ~ * and mixtures of44 F. E. Harris and C. T. O’Konski, J . Phys. Chem., 1957, 61, 310.45 R. C. Millar and C. P. Smyth, J . Anwr. Chenz. Soc., 1957, 79, 20.46 A. Di Giacomo and C. P. Smyth, ibid., 1956, 78, 2027.* 7 M. Freymann, J . Phys. Radium, 1956, 17, 326.* 8 R. J. Meakins, Trans. Furaday Soc., 1956, 52, 320.4g J. S. Dryden and S. Dasgupta, ibid., 1955, 51, 1661; J. W. Arnold and R. J.6 O J. S. Dryden, J . Chem. Phys., 1957, 26, 604.61 P. G. Harper and J. J. O’Dwyer, Proc. Phys. SOC., 1955, 68, A , 1184.62 J. S. Dryden and H. K. Welsh, Austra2. J. Sci. Res., 1951, 4, 616.53 R. H. Cole and S. Havriliak, Discuss. Faraday SOC., 1957, 23, 31; J .Chem. Phys.,54 S. Havriliak, R. W. Swenson, and R. H. Cole, ibid., p. 134.55 D. W. Davidson, Canad. J . Chem., 1957, 35, 458.6 6 H. E. Wirth and W. W. Wellman, J . Phys. Chew, 1956, 60, 919.5 7 L. Reinisch, Compt. rend., 1956, 242, 2915.58 A. Di Giacomo and C. P. Smyth, J . Amer. Chem. Soc., 1966, 78, 2032.Meakins, ibid., p. 1667.1955, 23, 2455NELSON DIELECTRIC MEASUREMENTS. 89dichloro-nitro-o-xylenes 59 have been studied by dielectric methods. Thethiols did not show the high dielectric constants and losses characteristic ofthe corresponding alcohols.Polymers.-Several reviews and books have 63* 62 Powles 63has correlated the dielectric, mechanical, and nuclear magnetic absorptionsof polyisobutene, poly(methy1 methacrylate), and poly(methy1 cc-chloro-acrylate) .The close relation between dielectric and mechanical relaxationprocesses, not always obvious from a comparison of the respective spectra,can often be shown when the data are treated by the method of reducedvariables described by Ferry et aZ.a In this treatment an empirical function( bT) was suggested to describe the temperature dependences of both electricaland mechanical relaxation processes in a remarkably wide range of systems;the universality of the function arises because the rates of all the processesdepend on temperature principally through their common dependence onfree volume. Activation energies evaluated from bT for poly(methy1acrylate) and several vinyl polymers were strongly temperature-dependentand larger than those found by Offergeld from conventional (linear) rateplots.65 Increase in chain-length of the side-groups in the acetals of poly-(vinyl alcohol) 66 increased the most probable relaxation time while theintroduction of bulky groups may prevent rotation completely, as doesbenzoylation of the hydroxyl groups in cellulose and ~tarch.6~ Carbonylgroups in polyethylene, which seem always to be present, can cause lossesover a wide range of frequencies and Mikhailov et aZ.68 have shown a directproportionality between the magnitude of the loss and the number of suchgroups present. Low- and high-frequency absorptions were attributed tothe movement of carbonyl groups in crystalline and amorphous regions,respectively, although both dispersion regions in polychlorotrifluoroethyleneare associated with processes in the amorphous zones.69 The effect ofplasticisers on the dielectric properties of poly(viny1 chloride), 70 poly(viny1-idene chloride),71 and amylose and amylopectin triacetates 72 has been in-vestigated. While the presence of plasticiser usually facilitates rotation ofpolar groups through the formation of a more open structure, decreasing the6D R. E. Wood and C. Boyars, J . Phys. Chem., 1956, 60, 1584.6o H. Stager, “ Werkstoff lrunde der Electrotechnischen Isolierstoffe,” Gebruder61 D. W. McCall, “ The Technology and Uses of Ethylene Polymers,” ed. Renfrew62 R. H. Norman, Proc. Inst. Rubber Ind., 1957, 4, 47.63 J. G. Powles, Arch sci. (Geneva), 1956, 9, Spec. No., 182.64 J. D. Ferry, M. L. Williams, and E. R. Fitzgerald, J . Phys. Chem., 1955, 59,403; M. L. Williams, R. F. Landel, and J. D. Ferry, J . Amer. Chem. Soc., 1955,77, 3701.66 G. Offergeld, Nature, 1956, 178, 1460.66 I. M. Erlikl and P. H. Shcherbak, Zhur. tekh. Fix., 1955, 25, 1575.67 P. Abadie, R. Charbonni&re, A. Gidel, P. Girard, and A. Guilbot, Compt. rend.,1955, 240, 1772; 1955, 241, 1137; see also C. W. Lewis and D. H. Hogle, J . PolymerSci., 1956, 21, 411.68 G. P. Mikhailov. S. P. Kabin, and B. I. Sazhin, Zhur. fekh. Fiz., 1955, 25, 590;G. P. Mikhailov, A. M. Lobanov, and B. I. Sazhin, ibid., 1954, 24, 1553.69 G. P. Mikhailov and B. I. Sazhin, ibid., 1956, 26, 1723.‘O P. Caillon and E. Groubert, Conzpt. rend., 1956, 242, 1313.71 B. L. Funt and T. H. Sutherland, Canad. J . Chem., 1955, 33,1669.7a C. F. Ferraro, J. J. Maurer, and W. T. Zager, J . Polymer Sci., 1956, 21, 427.Borntraeger, Berlin, 1955.and Morgan, Iliffe and Sons, London, 1957, ch. 890 GENERAL 4 N D PHYSICAL CHEMISTRY.activation energy and increasing the frequency of maximum absorption (fc) ,the opposite trend has been observed for amylose and amylopectin acetatesplasticised with, e.g., dimethyl phthalate, the branched-chain polymer showinga second dispersion at high freq~encies.~~ The loss in the unplasticisedsystems was attributed to co-operative motion of segments of neighbouringmolecules, and in the plasticised polymers to rotation of acetate groups. Itwas also suggested that the negative entropy value for the high-frequency dis-persion might be due to a decrease in the number of configurations availableto a branch-chain or segment before orientation. Plasticiser efficiency hasbeen related to the polarity of the plasticiser molecule 73 and to the enthalpyof acti~ation.~lThe Kirkwood-Fuoss theory of dielectric dispersion in polymer solutions,modified to include hydrodynamic interactions 74 between chain-segments,has been applied to van Beek’s data 75 for poly(viny1 acetate) in toluene atradio-frequences. 76 Theoretical and experimental values of the maximumreduced dispersion and activation energies agreed well, but the inversedependence offc on 2/M (where M is the molecular weight) required by theorywas not observed. van Beek and Hermans 77 have recently formulatedalternative equations based on a model in which each polymer molecule canbe subdivided into N sub-molecules whose ends carry electrical charges.Two dispersion regions were predicted, one at low frequencies (fccc 1/N2) andone at high frequencies (fc independent of N ) , neither region being dependenton M. Solutions of cellulose acetate in dioxan were studied and in this casefc depends on the degree of polymerisati~n.~~ The low-frequency loss (inexcess of that caused by D.C. conduction) observed for metal carboxylategels in non-polar solvents has been attributed to the hindered movement ofmicellar ions.79 Application of the Wagner-Sillars theory to the data forlead stearate in liquid paraffin suggests that the average shape of theparticles is that of a long prolate spheroid.81Adsorbed Molecules.-Both apparent polarisation and energy loss in avariety of systems under different conditions of surface coverage, tem-perature, and frequency have been measured. Plots of the electrical capacityof a condenser containing the solid-adsorbate system against volume of gasadsorbed usually show two almost linear sections. 82-86 With adsorbed ethylchloride, sulphur dioxide, and ammonia on non-porous rutile, studied by73 C. F. Ferraro and J. J. Maurer, J . Phys. Chem., 1956, 60, 382.74 W. G. Hammerle and J. G. Kirkwood, J . Chem. Phys., 1955, 23, 1743.75 L. K. H. van Beek, Thesis, Leiden, 1955.7 6 W. G. Hammerle and J. G. Kirkwood, J . Chem. Phys., 1956, 24, 1277.7 7 L. K. H. van Beek and J. J. Hermans, J . Polymer Sci., 1957, 23, 211; I.. deHrouchPre and L. K. H. van Beek, Rec. Trav. chim., 1956, 75, 355.78 P. C. Scherer, D. W. Levi, and M. C. Hawkins, J . Polymer Sci., 1957, 24, 19.70 S. M. Nelson, A. Gilmour, and R. C . Pink, J . , 1956, 3463.* O R. W. Sillars, J . Inst. Elect. Eng., 1937, 80, 378.81 J. Nesbitt and R. C. Pink, Paper presented a t Second International Congress ofSurface Activity, 1957.8a R. McIntosh, E. K. Rideal, and J. A. Snelgrove, Proc. Roy. SOL, 1951, A ,208, 292.83 L. N. Kurbatov, Zhur. $2. Khim., 1954, 28, 287.8p I. V. Zhilenkov, ibid., 1966, 30, 2519.86 G. Khodadadi, Compt. rend., 1957, 244, 198.88 M. Shimizu, J. Chem. Soc. Japan, 1964, 75, 885; 1955, 76, 1030, 1126NELSON DIELECTRIC MEASUREMENTS. 91McIntosh and his co-worker~,~~ the change in slope corresponded to the com-pletion of a unimolecular layer. The apparent polarisation at the higherlevels of adsorption approximated to that of the bulk liquid, whereas thatfor the incompletely covered surface was lower. In contrast, the apparentpolarisation of polar molecules adsorbed on silica gel decreased with increas-ing volume of gas a d s ~ r b e d . ~ ~ - ~ ~ $ ~ ~ The position of this discontinuity wasnot related to the area occupied by the adsorbed molecule, but rather to thenumber of adsorption centress8 This behaviour is believed to be charac-teristic of porous ad~orbents.8~ For butane and ethyl chloride on silica gel,two types of film, differing in density, were suggested, while for waterrotational freedom in the first adsorbed layer may be limited to two di-mensions. 82 Although various evaluations of the dielectric constant of theadsorbed species have been attempted,s8s 9O no entirely satisfactory formula isyet available. At least two dispersion regions have been observed for thesilica gel-water system.91392 Rolland and Bernard 91 attributed these to" free " and " bound " water, a Debye-type mechanism being implied.However, there is substantial evidence for a Maxwell-Wagner origin for theaudiofrequency loss. Heukelom and van Reijen 93 showed that the low-frequency dielectric constant was independent of the nature and quantity ofthe substance adsorbed. Kamiyoshi and Odaki g4 also favour an ionicmechanism, on the evidence of an increase of the heights with risingtemperature. In agreement with this view Zhilenkov 84 observed a move-ment of to higher frequencies on increasing the electrolyte con-centration in the gel. A change with time, from an " amorphous " to amore ordered structure, has been suggested for adsorbed water on variousglasses 95 and ionic crystals.g6 Both dipolar and ionic mechanisms havebeen suggested for certain clay mineral-water systems,97 the former seemingthe more probable; the positions of the loss maxima (lo2-lo7 c./sec.)indicate that the adsorbed water exists in a much more highly ordered statethan in liquid water and, under certain conditions, than in ice. The increasein fc with increase in adsorbate concentration was attributed to a disorderingeffect on the first adsorbed layer by molecules in the second layer. Themultiple adsorption sometimes observed may be due to water films ondifferent layer surfaces. Dipolar relaxation was also shown by adsorbedwater on c e l l u l ~ s e . ~ ~ ~ ~ ~ Muus 98 has ascribed the low-frequency loss (at lowwater contents) to the displacement of protons in hydrogen-bonds between87 M. H. Waldman, J. A. Snelgrove, and R. McIntosh, Canad. J . Chem., 1953,8 8 J. A. Snelgrove, H. Greenspan, and R. McIntosh, ibid., 1953, 31, 72; E. TIT.8g S. E. Petrie and R. McIntosh, ibid., 1957, 35, 183.g1 M. T. Rolland and R. Bernard, Compt. rent., 1951, 232, 1098.92 J. Le Bot and S. Montagner, ibid., 1951, 233, 862.93 W. Heukelom and L. L. van Reijen, J . Chinz. Phys., 1954, 51, 632.s4 I(. Kamiyoshi and T. Odake, J . Chem. Phys., 1953, 21, 1295.95 S. Kurosaki, S. Saito, and G. Sato, ibid., 1955, 23, 1846.O 6 J. Baruch and W. Low, BulE. Res. Couticil IsvaeE, 1953, 3, 31.O 7 J. Muir, Trans. Faraday Soc., 1954, 50, 249; B. J. Goldsmith, Thesis, Hull, 1950.98 L. T. Muus, Trans. Danish Acad. Tech. Sci., 1953, No. 4.9s R. Seidman and S. G. Mason, Canad. J . Chem., 1954, 32, 744.31, 998.Channen and R. McIntosh, ibid., 1955, 33, 172.G. C. Benson, E. W. Channen, and R. McIntosh, J . Colloid Sci., 1956, 11, 69392 GENERAL AND PHYSICAL CHEMISTRY.lccalised bound water molecules and hydroxyl groups of the polymer. Athigher water contents the absorption was characterised by a large activationenergy (38 kcal./mole) and was proportional to the quantity of non-localisedbound water.The Reporter thanks Mr. H. 13. Huang for his assistance.S. &I. N.F. D. S. BUTEMENT.C. KEMBALL.A. LEDWITH.H. MACKLE.S. M. NELSON.J. SHERIDAN.L. H. SUTCLIFFE.H. R. THIRSK.C. F. TIPPER