摘要:

J. Chem. SOC., Faraday Trans. I, 1982,78, 2843-2850 Kinetics of Flame Inhibition by Sodium BY DAVID E. JENSEN AND GEORGE A. JONES* Propellants, Explosives and Rocket Motor Establishment, Westco tt , Aylesbury, Buckinghamshire HP18 ONZ Received 5th February, 1982 When sodium is added at mole fractions of ca. to fuel-rich premixed hydrogen/oxygen/nitrogen flames of temperature T between 1800 and 2200 K, accelerated recombination of excess hydrogen atoms and hydroxy radicals is observed. The effect is quantitatively interpreted in terms of the reactions k, NaOH+H Na+H,O k -1 k2 k-* Na+OH+M $ NaOH+M. Rate coefficients are as follows: log,, (k1/cm3 molecule-' s-l) = - 10.75 0.5 -430 T-' log,, (k-,/cm3 molecule-' s-l) = - 9.39 f 0.5 - 9500 T-I log,, (k,/cms s-l) = - 26.30 & 0.4 - log,, T log,, (k-,/cm3 molecule-' s-I) = - 2.60 f 0.4 - log,, T- 17 100 T-'.An earlier paper' offered a quantitative kinetic interpretation of the ability of potassium to lower radical concentrations in hydrogen/oxygen/nitrogen flames. Like potassium, sodium has long been known to be capable of inhibiting flame propagation, and the important role played by gas-phase radical removal reactions in such inhibition has received considerable attention.,-* For fuel-rich flames the most likely reactions for sodium are the analogues of those invoked for potassium in ref. (1): NaOH+H-,Na+H,O (1) Na+OH+M +NaOH+M (2) where M is an energy-removing collision partner (usually H,O, H, or N, in H,/N,/O, flames). The purpose of the work described in the present paper was to test and quantify an interpretation of observed accelerations of flame radical removal by sodium based on these reactions.The only previously available values of the rate coefficients k , and k, of reactions (1) and (2), respectively, are order of magnitude estimates stemming from flame experiments not specifically designed for kinetic measurements: k , x 3.5 x lo-', exp(- 1000/T) cm3 molecule-' s-' and k, z 5 x T-l cmS molecule-2 s-l. EXPERIMENTAL The burner, additive supply systems and photometric technique used in this work were similar to those described previously.l? 5 9 The flames were atmospheric pressure, laminar, shielded, cylindrical, premixed, fuel-rich H,/O,/N, flames in which distance above (downstream of) the 2843 92-22844 FLAME INHIBITION BY SODIUM primary reaction zones was a linear measure of isothermal reaction time available for recombination of the free radicals produced in greater than equilibrium amounts in these zones.Under the conditions of this work, the only flame radicals present in significant proportions were H and OH, concentrations of such species as 0 and HO, being very low. Principal composition features, burned gas temperatures and post primary reaction zone flow rates are indicated in table 1. Flames 3-8 are an isothermal set, with temperature 2065 & 15 K, in which the burned gas mole fraction of H, varies from 0.125 to 0.39. Care was taken to eliminate errors from slight temperature drift across the set by the method of Cu resonance line emission described in ref. (7).TABLE 1 .-FLAME TEMPERATURES AND COMPOSITIONS ~~ [H,Ol/ w 2 1 / [HI,,/ [HI 3 d [OH1 3 J reaction H,/N,/O, 10’’ molecule lo1’ molecule 10l5 molecule 1015 molecule 10l5 molecule flame (unburned) ~ r n - ~ ~ m - ~ ~ m - ~ ~ r n - ~ ~ m - ~ T/K (3 cm)/ms time 3.5/6.0/ 1 .O 4.0/5.0/ 1 .O 5.0/3.0/1.0 4.0/4.0/ 1 .O 3.5/4.5/1.0 3.2/4.8/1 .O 3.3/4.0/1.0 4.5/3.5/1.0 3.0/5.0/ 1 .o 8.6 8.6 8.9 8.9 8.9 8.9 8.9 8.9 9.3 6.4 8.6 14.0 11.0 9.0 6.8 5.4 4.5 6.1 0.74 1.7 5.6 5 .O 4.5 3.9 3.5 3.1 7.2 10.7 11.7 17.2 15.5 13.0 10.2 8.9 7.8 11.2 1 .o 1 .o 1.3 1.4 1.5 1.5 1.7 1.7 2.3 1830 1930 2065 2065 2065 2065 2065 2065 2180 0.99 0.99 1.03 1.03 1.03 1.03 1.03 1.03 1.08 [HI,, and [HI 3,, are hydrogen atom concentrations for equilibrium and for 3 cm downstream of the primary reaction zones, respectively.T is the measured Na D-line reversal temperature of the burned gases, which in every case is slightly elevated above that corresponding to no heating of the unburned gases [cf., e.g., ref. (14)]. Calculations based on thermochemical and kinetic data taken from ref. (8)-( I 1) strongly suggest that no sodium-containing species other.than Na and NaOH is formed in the flames of, this work in concentrations high enough to contribute significantly, in the present context, either to reaction rates or to p a ] , (the latter defined as C, si [S,], where [S,] is the concentration of the ith Na-containing species in the flame, which itself contains si sodium atoms per molecule). It is therefore assumed throughout this paper that ma], = “a] + [NaOH] and that reactions of sodium-containing species other than Na and NaOH are negligibly slow, although in view of the large uncertainties in some of the data used, independent confirmation of the validity of this assumption would be welcome.Sodium was added to the flames at concentrations “a], of 1014-1015 molecule cmL3 (mole fractions between 3 x as sodium dipivaloylmethane, [(CH,),CCO],CHNa, in the form of vapour from the supply reser~oir.~ Deposition of additive in the supply system and burner was minimised via heating of both (to a temperature slightly higher than was needed in the case of potassium’), but, because of doubts concerning the extent of deposition, in situ determinations of the delivery of sodium to the flames were made. For the purposes of these determinations, sodium was first supplied to the flames at known concentrations in the range 1 x lolo d [Na],/molecule cm-3 < 3 x 1013 from a calibrated atomiser5 and the curve of growth of ZNa*, the integrated emission intensity of the two components of the Na D-lines taken together, against [Na] was constructed.A small correction was made in the calculation of [Na] from “a], and [HI (measured as described below) for hydroxide formation on the assumption that reaction (1) is balanced, i.e. that (ma] [H,O])/([NaOH] [HI) = K,, where the equilibrium constant Kl = 0.043 exp (20900/T).s7 For “a], = [Na] (1 + [NaOH]/[Na]) > 4 x 1 011 molecule ~ m - ~ , the curve of growth was in the regime where IN&* = c[NaI0e5, where c is a constant. Sodium was then supplied to the flames at 1 x IOl4 < [Na],/molecule cm-3 < 1 x 1015 via addition of the dipivaloylmethane complex to the supply reservoir, [Na] obtained from J2Na*/c2 and the corresponding value of [Na], again calculated from measured [HI and Kl.The departures from balance of reaction (1) inferred below do not introduce significant errors into this calibration and 3 xD. E. JENSEN A N D G. A. JONES 2845 procedure, from which "a], is obtained with a precision of & 30%, because they are relatively small and because [NaOH]/[Na] is in any case always + 1. Hydrogen atom concentrations were measured by the Li/Na comparison method1, with an accuracy of ca. & lo%, lithium being supplied to the flames in known proportions from the atomiser and relative values of ILi* in the presence of trace and additive concentrations of sodium being determined.Because background interference from the alkali-metal continuum13 was significant at the high concentrations of sodium resulting from the addition of the dipivaloylmethane compound, it was necessary to employ values of [Li], as high as 4 x lo1, molecule ~ m - ~ . This meant that, in measurements of [HI, ILi* was proportional to [Li]o.5 rather than to [Li], with consequent loss of sensitivity to changes in [HI; even with this loss, however, the main factor determining the precision of the results was the reproducibility of delivery of sodium additive from the reservoir rather than the means of measuring [HI, so the penalty paid for working in the square-root regime was not severe.Equilibrium data for LiOH formation were taken from ref. (14). Hydroxy radical concentrations were calculated from [HI on the assumption that the rapid reaction H+H,O+OH+H, ( 3 ) [equilibrium constantY K3 = 4.3 exp (-7530/T); rate coefficient15 k, = 1.6 x exp (1 0 IOO/ T ) cm3 molecule-' s-l] is balanced throughout the burned gases. All photometric measurements were made at distances downstream from the primary reaction zones of 10-40 mm, in which region concentrations of the major flame constituents H,O, H, and N,, as well as temperatures, were, to a close approximation, constant. RESULTS A N D INTERPRETATION In the absence of any additive, the recombination of H and OH radicals in the burned gases may be described16 in terms of the reactions H+H+M+H,+M (4) H+OH+M + H,O+M (5) where [MI is the sum of concentrations of all flame molecules, k , = 2 x T1 and k? = 1.6 x T1 cm6 molecule-2 s-l.These values of k , and k , agree satisfactorily with other literature values.15* l7 The acceleration of hydrogen atom removal stemming from addition of sodium to the flames is illustrated in fig. 1, where [HI-' is plotted against reaction time for flame 5 (2065 K) without sodium added and for values of "a], varying from 1 x lo1* to 5 x 1014 molecule cm-,. That part of the recombination due to the presence of sodium is proportional to "a],, a feature consistent with a homogeneous acceleration process. Similar results were obtained for the other flames. Results for different temperatures and compositions are shown in fig. 2 and 3. Addition of the volatile ligand 2,2,6,6-tetramethyl-3,5-heptadione alone to the flames at concentrations equivalent to those introduced by the corresponding sodium compound caused no significant changes in flame temperature or composition ; the observed acceleration of flame radical recombination may therefore be attributed entirely to the influence of sodium.The observed decreases in radical concentrations caused by addition of sodium to the flames are considerably greater than "a],. Any interpretation of the effect must therefore be based on a cyclic, catalytic, reaction sequence involving the regeneration of Na and NaOH. A computer program16 was used to find values of k , and k , which, in combination with the known values of k,, k, and k,, made it possible to account for all measured [HI at different flame temperatures, compositions and "a], in terms of the simple regenerative cycle consisting of reactions (1) and ( 2 ) and the other three reactions.Both forward and reverse steps of each reaction were included in every2846 FLAME INHIBITION BY SODIUM 9" 0.5 1.0 1.5 react ion t ime/ms FIG. 1.-variation with reaction time of [HI-' in flame 5 (2065 K) for different concentrations (molecule cm+) of added sodium: A, ma], = 0; B, "a], = 1.0 x 1014; C, [Na]. = 2.4 x D, "ale = 4.0 x E, "a], = 5.0 x Lines correspond to best-fit rate coefficients obtained from all experiments. TABLE 2.-EQUILIBRIUM CONSTANTS AND RATE COEFFICIENTS OF REACTIONS reaction equilibrium constant rate coefficient H+H+M + H,+M 3.8 x exp (52650/T) 2 x T-' H+OH+M + H,O+M 8.9 x exp (60 180/T) 1 .6 ~ loF2* T-' H+H20+H,+OH 4.3exp(-7530/T) 1.6 x 10-lo exp (- 10 100/T) NaOH + H + Na + H,O 0.043 exp (20 900/T) 1.8 x lo-" exp (- lOOO/T) Na+OH+M +NaOH+M 2 . 0 ~ exp (39 300/T) 5 x lo-,' T-' source reference for rate coefficient 16 16 15 this work this work Units of molecule ~ r n - ~ s-l used throughout. Equilibrium constants from ref. (8), based on ref. (9).D. E. JENSEN AND G. A. JONES 2847 I I 0.5 1.0 reaction time/ms FIG. 2.-[H]-l as functions of reaction time for different flame temperatures. A, 1830 K, “a], = 6.0 x lOI4 molecule C, 2180 K, “a], = 5.0 x lOI4 molecule ~ m - ~ . A,, B, and C, are corresponding functions for “a], = 0. Lines correspond to best-fit values of rate coefficients obtained from all experiments.B, 1930 K, “a], = 6.5 x lOI4 molecule computation, the ratio of forward rate coefficient kj to reverse rate coefficient k-j for thejth reaction being equated to the equilibrium constant Kj. Values of Kj used are shown in table 2. Computed concentrations and reaction rates for the times of interest were insensitive to initial (time = 0) values of [NaOH]/[Na]. Computations in which k , and k , were set equal to the previously estimated* values k: = 3.5 x exp (- 1000/T) cm3 molecule-’ s-’ and kg = 5 x T1 cm6 s-l produced rates of radical removal lower than those observed experimentally. For these values of k , and k,, reaction (1) is calculated to be close to balance and upwards revision of k , does not greatly increase the calculated rate of radical removal.It may therefore be inferred immediately that the true value of k , exceeds k:. An excellent fit to the observations is obtained with k, = 10 k: and2848 FLAME INHIBITION BY SODIUM I I 0.5 1.0 1 reaction time/ms FIG. 3.--[H]-' as functions of reaction time for different flame compositions at 2065 K. Numbers attached to lines are those of the flames used. For flames 3 and 5, ma], = 5.0 x 1014 molecule ~ m - ~ . For the other flames, ma], = 4.0 x 1014 molecule ~ m - ~ . Lines correspond to best-fit values of rate coefficients obtained from all experiments. Results for flame 8 with "a], = 2.0 x 1014 molecule are omitted because they almost coincide with those shown for flame 7. k , = 5 ky. Increasingly less satisfactory fits are obtained as k, is increased above 10 kg and k , correspondingly decreased below 5 k;, the fit for k, = 20 k; and k , = 1.5 k: being barely adequate.Computations in which k, lies outside the range (1.5-5)kf or k, outside the range (1 0-20)kg lead to significant discrepancies with experiment. The best values of k , and k, emerging from analysis are thus 1.8 x loLZ1 exp (- 1000/T) cm3 molecule-' s-l and 5 x s-', respectively. The computed lines of fig. 1-3 correspond to these values. Calculated rates of reactions for conditions of negligible ("a], = 8.2 x 1Olo molecule ~ m - ~ ) and significant ("a], = 5 x 1014 molecule ~ r n - ~ ) accelerations of radical removal are illustrated in table 3. r1 cmsD. E. JENSEN AND G. A. JONES 2349 The uncertainties in k, and k , are hard to specify precisely; possible errors in measurement of [Na] and [HI and in K, and K, all contribute.Estimated overall errors, however, are such that k, and k, may reasonably be expressed by log,, (k,/cm3 molecule-l s-I) = (- 10.75 0.5) -430 T-' and log,, (k,/cm6 molecule-2 s-l) = - 26.30 &- 0.4 -log,, T. Despite this convenient formal association of error bounds with the temperature-independent terms for the relatively narrow temperature range of this work, there is substantial uncertainty in the temperature dependences of both k , and (especially) k, [cf. ref. (l)]. Future measurements of these coefficients at lower temperatures would be highly desirable. TABLE 3.-cALCULATEiD REACTION RATES FOR FLAMES CONTAINING SODIUM rates for "a], = 8.2 x 1Olo molecule ~ 1 1 1 ~ ~ rates for "a], = 5.0 x lOI4 molecule ~ r n - ~ reaction forward reverse net forward reverse net H+H,O+OH+H, 2 .2 9 ~ loz2 2 . 2 8 ~ 10'' 1 . 1 6 ~ lo'' 1 . 7 9 ~ 10'' 1 . 7 9 ~ 1 . 1 5 ~ 10'' H+H+M+H,O+M 1 . 6 3 ~ 1 0 ' ~ 7 . 1 5 ~ 1 0 ' ~ 1 . 5 5 ~ 10l8 1 . 0 ~ 1 0 ' ~ 7 . 1 7 ~ 1 0 ' ~ 9 . 2 9 ~ 1 0 " H+OH+M -P H,O+M 1.46 x 10" 6.20 x 1017 1.40 x lo'' 8.97 x 10l8 6.21 x 1017 8.35 x 10l8 NaOH+H + Na+H,O 2 . 0 4 ~ 1015 6.67 x 1014 1.37 x 1015 1.02 x 10'' 4.05 x 10l8 6.17 x 10l8 Na+OH+M -+ NaOH+M 1.58 x 1015 2.07 x 1014 1.38 x I O l 5 7.52 x 10l8 1.32 x 10l8 6.20 x lo1* Rates calculated for a distance downstream from the primary reaction zones of 15 mm in flame 5 (2065 K). Computed rates at this distance are insensitive to the initial ( t = 0) ratio of [NaOH] to "a].All rates in molecule ~ m - ~ s-l. Initial concentrations: [H,] = 9 x lo1', [H,O] = 8.9 x lo1', [HI = 6.5 x 1Ol6 and [OH] = 7.3 x lOI5 molecule ~ m - ~ . DISCUSSION AND CONCLUSIONS The observed accelerations of radical removal may be satisfactorily interpreted in terms of contributions from reactions (1) and (2), with rate coefficients k , = 1.8 x 10-l' exp (- 1000/T) cm3 molecule-' s-l k-, = 4.1 x 1 0-lo exp ( - 2 1 900/ T ) cm3 molecule-l s-l k, = 5 x T-l cm6 s-l k-, = 2.5 x T-l exp (- 39 300/T) cm3 molecule-' s-l. The value of k, is approximately equal to that found for the corresponding potassium reaction., The pre-exponential terms in both k - , and the corresponding rate coefficient for potassium closely approach the collision frequency. That the best value for k, exceeds the best value for the rate coefficient of the potassium analogue of this reaction' by a factor of ca.3 is perhaps at first sight surprising, but it must be remembered that the factor of uncertainty in each value is large and that theoretical estimates of these rate coefficients would be expected to be sensitive to details of the interaction potentials for alkali atom, OH and M. Reaction (1) is seen here as not being balanced even under conditions of negligible acceleration of radical removal (cf. table 3). This does not imply that previous flame determinations of the bond energy of Na-OH,18-20 resting on the assumption that balance is achieved, are significantly in error: the determinations of ref. (1 8) and (19) rely largely on measurements performed for hotter flames, where departures from balance of reaction (1) are smaller, and that of ref.(20) invokes a method of analysis of results which makes potential errors stemming from imbalance small.,,2850 FLAME INHIBITION BY SODIUM As in the corresponding work on potassium,' [MI has been set equal to the total concentration of all flame molecules throughout. No apparent variation of k , [MI with isothermal composition was observed. This observation, however, would be consistent with any one of three possibilities: (a) all three major flame species H,O, H, and N, have roughly equal efficiencies as M in reaction (2); (b) H,O is much more efficient than both H, and N,; (c) H,O is much less efficient than H, and N, and the latter two have approximately equal efficiences.Further work aimed at distinguishing amongst these possibilities would be welcome, as would an investigation of the pressure dependence of reaction (2). D. E. Jensen, G. A. Jones and A. C. H. Mace, J. Chem. SOC., Faraday Trans. I , 1979, 75, 2377. * K. Sridhar Iya, S. Wollowitz and W. E. Kaskan, 15th Inr. Symp. Combustion (The Combustion Institute, Pittsburgh, 1975), p. 329. W. A. Rosser, S. H. Inami and H. Wise, Combust. Flame, 1963,7, 107. R. Friedman and H. Levy, Combust. Flame, 1963, 7, 195. D. E. Jensen and G. A. Jones, J. Chem. SOC., Faraday Trans. I , 1972, 68, 259. D. E. Jensen and G. A. Jones, J. Chem. SOC., Faraday Trans. I , 1973, 69, 1448. 'I D. E. Jensen and G. A. Jones, Proc. R. SOC. London, Ser. A , 1978,364, 509. a D. E. Jensen and G. A. Jones, Combust. Flame, 1978, 32, 1 . JANAF Thermochemicaf Tables, ed. D. R. Stull and H. Prophet, NBS NSRDS No. 37, 1971. Supplement 1: J. Phys. Chem. Re5 Data, 1974, 3, 311. lo D. Husain and J. M. C. Plane, J. Chem. SOC., Faraday Trans. 2, 1982, 78, 163. l1 D. E. Jensen, J. Chem. SOC., Faraday Trans. I , 1982, 78, 2835. l2 E. M. Bulewicz, C. G. James and T. M. Sugden, Proc. R. SOC. London, Ser. A, 1956, 235, 89. l3 C. G. James and T. M. Sugden, Proc. R. SOC. London, Ser. A, 1958, 248, 238. l4 D. E. Jensen and G. A. Jones, J. Chem. SOC., Faraday Trans. I , 1975, 71, 149. l5 D. L. Baulch, D. D. Drysdale, D. G. Home and A. C. Lloyd, Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1972), vol. 1. l6 D. E. Jensen and G. A. Jones, J. Chem. Phys., 1974, 60, 3421. l7 G. Dixon-Lewis and D. J. Williams, Comprehensive Chemical Kinetics, volume 17: Gas-phase la D. E. Jensen and P. J. Padley, Trans. Faraday SOC., 1966, 62, 2132. *O D. H. Cotton and D. R. Jenkins, Trans. Faraday SOC., 1969, 65, 1537. Combustion, ed. C . H. Bamford and C. F. H.'Tipper (Elsevier, Amsterdam, 1977), chap. 1 . R. Kelly and P. J. Padley, Trans. Faraday SOC., 1971, 67, 740. D. E. Jensen, Combust. Flame, 1972, 18, 217. (PAPER 2/2 15)

ISSN:0300-9599    

DOI:10.1039/F19827802843

出版商:RSC    

年代:1982

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1982,78, 2851-2860 Hydrophobicity of Amino-acid Molecules Solvation of Amino-acid Hydrobromides in Mixtures of Water and NN-Dimethyl formamide BY MEINDERT BOOIJ AND Gus SOMSEN* Department of Chemistry, Free University, De Boelelaan 1083, 108 1 HV Amsterdam, The Netherlands Received 15th February, 1982 Enthalpies of solution of 8 amino-acid hydrobromides are measured calorimetrically in NN- dimethylformamide + water mixtures at 298.15 K over the whole composition range. A deviation from linear behaviour at high water content for the alkyl-substituted 2-amino acids is considered to result from hydrophobic hydration. This effect becomes more pronounced when it is considered with respect to glycine-HBr. The solvation of the alkyl groups is described by a hydrophobic hydration model involving two adjustable parameters, i.e.the enthalpic effect of the hydrophobic hydration and a measure of the number of water molecules in a clathrate-like structure around an alkyl group. Trends in the enthalpic contributions of the alkyl groups parallel those obtained for other compounds and the commonly used but more arbitrary measures of hydrophobicity based on the transfer properties of amino acids. Hydrophobicity has been a much debated subject among biochemists and physical chemists in the last decades.l It manifests itself in hydrophobic hydration: the entropically unfavourable solution of apolar molecules (or residues) in water. Recently our group proposed a model to describe the enthalpic effect of hydrophobic hydration.2 In this model cooperative formation of hydrogen-bonded clathrate-like ‘structures’ of water around apolar groups is assumed.These entities, which are differently structured from bulk water, break up upon introduction of a cosolvent. NN-Dimethylformamide (DMF) proved to be a particularly suitable cosolvent as it is aprotic and its dielectric constant is not so low as to cause extensive association of ions. The hydrophobicity of the side-chain of an amino acid is a useful concept in discussions about spatial structures of globular proteins. It is now possible to make predictions about the three-dimensional structure of a protein with the aid of computer calculations in which the hydrophobicity, in addition to a number of other properties of amino-acid side chains, is A recent illustration of this is the work by Akeroyd et al.on the hydrophobic, phosphatidyl choline transfer p r ~ t e i n , ~ for which an X-ray structure determination has not yet been determined. The commonly used measure of hydrophobicity is the scale proposed by Nozaki and T a n f ~ r d , ~ which was completed for all twenty natural amino acids by Jones.6 It was assumed that the interior of a protein is similar to a non-aqueous solvent. The Gibbs energy of transfer for a side chain A(AG:r), or Ah’r in the notation of ref. (9, i.e. the difference AGE (amino acid) -AGE (glycine) from the non-aqueous medium to water, was taken as a quantitative measure of hydrophobicity. Depending on the solubility of the amino acid the non-aqueous medium was chosen as ethanol, 1,4-dioxan, butanol or acetone.In our previous papers [see ref. (2)] we derived a quantity Hb(W) for a number of molecules which we consider to be a quantitative measure of their hydrophobic 285 12852 HYDROPHOBIC IT Y OF AM INO-A C I D MOLECULES properties. In order to test the usefulness of this concept further we decided to extend our investigations to amino-acid molecules. With this aim we have measured enthalpies of solution of several amino-acid hydrobromides in DMF + water mixtures. The values obtained for Hb(W) are compared with the hydrophobicity given in the literature on the basis of the solubility of amino acids, particularly in ethanol + water mixtures. Our choice of DMF as a cosolvent is also attractive because DMF contains a peptide bond.In this respect it might be a suitable model for the protein interior. Calorimetric measurements of enthalpies of solution of amino acids in water are scarce; one example is the work of Spink and Auker’ on mixtures of water and ethanol up to mole fraction XEtoH = 0.30. More enthalpic data can be derived from the temperature dependence of the solubility, but this method does not generally provide accurate thermodynamic quantities. Also, the solubility of amino acids with alkyl side chains is small in non-aqueous solvents.8 Moreover, they dissolve slowly and tend to float on the surface of the solvent, which makes accurate measurements cumbersome. Therefore, we decided to use the hydrobromic acid salts of the amino acids, which dissolve in pure DMF virtually instantaneously.In this way we are able to consider enthalpic properties of all amino-acid molecules with respect to one non-aqueous solvent only, which because of the solubility problems proved difficult with amino acids themselves. As the neutral amino acid occurs in the zwitterionic form, the HBr salt differs from it in the protonation of the carboxylate group. We assume that this protonation does not influence the hydrophobic properties of the molecules to a large extent. This assumption is substantiated by a comparison of previous results on substituted ammonium bromides and amine~.~ EXPERIMENTAL The enthalpies of solution were measured with an LKB 8700-1 precision calorimetry system equipped with a 100 cm3 vessel. The experimental procedure and test of the calorimeter have been reported before.lO DMF (Baker, analysed reagent) was stored over molecular sieves (Baker 4A) and used without further purification.The solvent mixtures were prepared by mass and distilled deionized water was used. Table 1 gives the source and the purity of the reagents. The hydrobromides were prepared by the method of Frost:11 a small excess of freshly distilled concentrated hydrobromic acid (Baker, analysed reagent) was added to a hot concentrated aqueous solution of the amino acid. Upon evaporation of the solvent the hydrobromides crystallized, were filtered and dried in U ~ C U O over KOH and subsequently over P,O,. Table 1 TABLE l.-sOURCE AND PURITY OF THE REAGENTS R in stated purity R-CH-COOH purity HBr salt I reagent abbreviation source (%) (%) NH,+ gl ycine L-alanine ~~-2-aminobutyric acid L-valine m-norvaline L-leucine L-isoleucine 4-aminobutyric acid glY ala 2-aba Val norval leu ile 4-aba Baker Baker Fluka Merck Fluka Merck Merck Merck 99.6 99 99 99 99 99 99 98 99.2f0.1 H 98.7fO.1 CH, 99.1 f 0.3 CH,CH, 99.1 & 1 .O (CH,),CH 99.4 +_ 0.1 CH3(CH2)2 100.1 & 0.I (CH,),CHCH, 100.0+0.7 98.3 & 0.5 CH,CH,CH(CH,) -M. BOOIJ A N D G. SOMSEN 2853 states the final purity as judged from the Br- content, which was obtained by potentiometric titration with AgNO,. As all hydrobromides are hygroscopic and corrosive, they were handled in a dry box and contact with metal was avoided. RESULTS The measurements of the enthalpy of solution AH,,, were carried out in such a way that the final concentrations ranged from 1 x loe3 to 1 x mol dmV3.All enthalpies of solution refer to a temperature of 298.15 0.05 K. The value of AH,,, was generally taken to be the average, after corrections as outlined below, of 2-4 measurements agreeing within 0.4 kJ mol-l. The process of interest is the dissolution of the solid amino-acid hydrobromide (aaHBr) in DMF +water mixtures to the protonated amino-acid ion (aaH+) plus the free bromide ion. The actual calorimetric process yields a solution containing aaH+, Br-, the zwitterion, H+ and the ion-pair aaH+-Br-. Therefore several corrections should be applied. First, a correction was made for the dissociation of aaH+ to its zwitterion. For the calculations of the degree of dissociation a, in water we used values of the acid dissociation constants Kdiss and the corresponding enthalpies AHdiss compiled by Martell and Smith.', In order to estimate the values of AHdiss and pKdiss in DMF it was assumed that the changes in these properties when aaH+ is transferred from DMF to water are equal to the same changes for acetic acid (HAc).For the latter we used PKdis, = 4.76 in water12 and p&i,s = 13.4 in DMF,13 and AHdiss = - 0.4 kJ mol-1 in water12 and AHdiss = €7.5 kJ mo1-l in DMF.13 Moreover, the assumption was made that these quantities vary linearly with the mole fraction of water. This gives PKdiss(aaHf~ xW) = (XW - l ) [p&is,(HAc, W)-pKdiss(HAc7 DMF)l +pKdiss(aaH+, w, (I) and an analogous expression for AHdiss. In pure water this correction is generally < 1.6 kJ mol-l, except for glycine, owing to its relatively large enthalpy of dissociation.The corrections become negligible for Xw < 0.5. Secondly, from conductometric studies14 it is known that alkylammonium bromides are not fully dissociated in pure DMF. To calculate the degree of dissociation a, we adopted the value of the association constant Kass = 125 dm3 mol-l determined for ethylammonium bromide.14 De Visser and Somsen15 calculated AH,,, = 4.9 f 0.5 kJ mol-l for three tetra-alkylammonium bromides from the concentration depen- dence of the enthalpy of solution. In our case the combination K,,, = 125 dm3 mol-l and AHass = 5 kJ mol-1 described the concentration dependence in pure DMF well, and was used for all salts except norvaline-HBr (see below). A third and generally small (< 0.4 kJ mol-l) correction was made to allow for the concentration dependence of the enthalpy of dilution according to the limiting Debye-Huckel law.For a 1 : 1 electrolyte the apparent molar enthalpy of solution at infinite dilution AHm is given by16 AHgI = AH,,, -3SH c$. (2) For the Debye-Huckel slope S , in water a value of 2.962 kJ mol-g dmg was used. The value of SH in DMF, 7.50 kJ mol2 dmg, was calculated from ref. (17). Also, in this instance SH was interpolated linearly as a function of Xw. Summarizing, we have2854 HYDROPHOBICITY OF AMINO-ACID MOLECULES TABLE 2.-sTANDARD ENTHALPIES OF SOLUTION, AHgI, OF SOME AMINO-ACID HYDROBROMIDES IN MIXTURES OF WATER AND DMF AT 298.15 K AH&kJ mol-l DL-2-aminobutyric- XW gl ycine-HBr L-alanine-HBr acid-HBr 0.000 0.060 0.189 0.325 0.450 0.550 0.650 0.770 0.850 0.900 0.950 1 .ooo - 28.98 f 0.26 - 26.97 f 0.13 -24.21 fO.10 - 20.25 f 0.05 - 15.39 f 0.06 - 10.16f0.10 - 3.87 f 0.04 4.14 f 0.16 8.62 k0.02 11.14fO.08 13.22f0.08 13.50+0.03 - 31.48 & 0.14 - 29.88 f 0.14 - 27.41 f 0.09 - 24.18 f 0.07 - 20.1 1 f 0.02 - 15.23f0.19 -9.36f0.11 - 1.51 fO.10 2.85 f 0.08 4.75 f 0.12 6.05 f 0.08 5.90 f 0.02 - 26.85 & 0.08 - 25.19 & 0.14 - 22.73 & 0.08 - 19.26 f 0.01 - 15.03f0.17 - 10.05 f 0.20 - 3.93 f 0.04 3.51 fO.10 7.35 0.04 8.83f0.10 9.18 f 0.12 8.1 4 f 0.07 ~~-4-aminobutyric- acid-HBr L-valine-HBr L-norvaline-HBr 0.000 0.060 0.189 0.325 0.450 0.550 0.650 0.770 0.850 0.900 0.950 1 .ooo - 15.97 +_ 0.05 - -11.79k0.18 - - 3.87 f 0.03 6.35 +_ 0.08 17.92 f 0.05 20.1 1 & 0.04 21.93 f 0.06 22.74 & 0.14 - -26.56k0.20 - 24.12 f 0.18 - 22.10 f 0.06 - 18.03f0.18 - 13.81 f O .1 1 - 9.02 f 0.19 -2.81 f0.17 4.37 f 0.22 8.16 f 0.17 9.20 _+ 0.14 9.00 f 0.13 7.22 & 0.13 -28.10 (see text) - 25.68 f 0.28 -23.59f0.13 - 20.32 f 0.02 - 14.47f0.10 - 8.79 f 0.09 -3.21 f0.06 4.47 f 0.05 8.30 f 0.08 9.49 f 0.04 9.25 f 0.01 7.01 f 0.06 AH$&/kJ mo1-I X W L-leucine-HBr L-isoleucine-HBr 0.000 0.060 0.189 0.325 0.450 0.550 0.650 0.770 0.850 0.900 0.950 1 .ooo - 26.35 f 0.06 - 28.79 & 0.45' -21.66f0.06 - 17.80f0.05 - 12.92f0.12 - 7.57 f 0.02 - 1.25f0.13 6.25 f 0.03 10.71 k0.03 11.58 k 0.06 10.65 f 0.08 7.84 & 0.05 -29.81 kO.10 - 27.50 f 0 . 14 - 25.06 f 0.26 - 21.98 f 0.08 - 17.29 & 0.09 - 11.89f0.12 - 5.29 f 0.05 2.97 f 0.04 6.67 f 0.22 7.49 +_ 0.01 6.77 & 0.11 4.08 f 0.13 ' We suspect that this large uncertainty is due to association.Indeed, application of a correction similar to that in pure DMF yields a much smaller uncertainty. However, lack of data prevents us from accounting in a reliable way for association in the solvent mixtures.M. BOOIJ AND G . SOMSEN 2855 where all corrections for our systems are in the exothermic direction. After these corrections systematic deviations from a constant AHZl were absent. AHgl can now be identified as the standard molar enthalpy of solution AH&$ of aaHBr. Values of AH$J for the different compounds are given in table 2. The uncertainties quoted in this table are average deviations from the mean final value. This procedure was not applicable to norvaline-HBr in DMF.Here two batches of material gave different results. In both cases enthalpies of solution were observed which implied stronger association than in the other cases. On graphical extrapolation the results of both batches yielded coinciding values at infinite dilution. The value in table 2 is evaluated according to this procedure. DISCUSSION The results in table 2 show that at low Xw, AHgl of all compounds increases with increasing water content and exhibits an inflexion near Xw = 0.7. However, at high Xw different behaviour is observed: for two of the compounds studied, glycine-HBr and 4-aminobutyric acid-HBr there is a further increase in AHgl up to X , = 1, while for the other compounds AHgl reaches an endothermic maximum between X , = 0.80 0 0.25 0.50 0.75 1.00 xw FIG.1 .-Enthalpies of solution of some amino-acid hydrobromides in DMF+ water mixtures at 298. I5 K. x , glycine-HBr; 0, valine-HBr; W, isoleucine-HBr; A, Caminobutyric acid-HBr.2856 HYDROPHOBICITY OF A MI NO-A C ID MOLECULES and 0.90, after which a decrease in AHgl to the value in pure water occurs. Some representative curves are shown in fig. 1 ; the shapes of the curves for norvaline-HBr and leucine-HBr, which are not given in fig. 1, show only small differences with those of their isomers, valine-HBr and isoleucine-HBr, respectively. The general behaviour of these compounds is comparable to that of ammonium salts:2 ammonium bromide, like glycine-HBr, exhibits this continuous increase in AHgl upon going from DMF to water.On the other hand, leucine and isoleucine, which are butyl-substituted glycines, show a similar maximum in AHgl as butylammonium bromide. Also the magnitudes of the maxima, ca. 4 kJ mol-1 with respect to the value in pure water, are approximately equal. Comparable exothermic shifts upon a decrease of the amount of cosolvent to zero have been found for hydrophobic solutes of several types and can be considered as a unique property of water. The other 2-amino-acid hydrobromides show behaviour intermediate between glycine-HBr and the leucine salts. In 4-aminobutyric acid-HBr, however, the behaviour is different. Apparently the terminal ammonium group provides a close resemblance to the solution properties of glycine-HBr. This corroborates the previously found gradual disappearance of the endothermic maximum upon successive substitution of the tetraethylammonium ion with terminal hydroxy groups.Again it shows that alkyl chains separating two not too distant polar groups do not exhibit hydrophobic properties. These distinctions can be illustrated in a more quantitative manner by means of the enthalpies of transfer, AHg (DMF + W). This quantity decreases with increasing chain length, as was also observed earlier, e.g. with a series of alcohols as solutes,18 where little change in AHP (DMF + W) was observed when the number of carbon atoms in the chain, a,, was > 3. In this study the earlier finding18 that AHt? (DMF + W) is more endothermic for a straight chain than for a branched chain is confirmed: AH$ (DMF + W) of norvaline-HBr (35.1 k0.3 kJ mol-l) is ca.1.3 kJ mol-1 more positive than the value for valine-HBr. Unfortunately, a compound to test this apparent rule further, norleucine-HBr, proved to be extremely hygroscopic and could not be obtained in a purity high enough for calorimetry. In order to emphasize the influence of the alkyl groups the transfer properties were also expressed relative to those of glycine-HBr. Curves resulting from this procedure are shown in fig. 2, which shows that these difference quantities expose the peculiar influence of the different alkyl groups more clearly. They also have the additional advantage that errors in the assumptions necessary to obtain AHg1 (see above) tend to cancel, to a large extent. In fig. 2 the relatively small deviations from linear behaviour for alanine and 4-aminobutyric acid stand out.For the other compounds much larger deviations occur. This phenomenon can be described by our hydrophobic hydration model, which for differences in enthalpies of solution (AHgJ between amino-acid hydrobromides and glycine-HBr in solvent mixtures M gives the equation Eqn (4) can be written in terms of enthalpies of transfer as A(AHg1, M) = Xw A(AHg1, W) + (1 -Xw) A(AHg1, DMF) + (XG -xw) Hb(W). (4) A(AHg, W + M) = (1 - Xw) A(AHg, W + DMF) + (XG - Xw) Hb(W). (5) It is eqn ( 5 ) which is represented in fig. 2. The last term in eqn (4) and ( 5 ) represents the deviation from linearity and determines the shape of the curves relating A(AHgl) and Xw. It contains two parameters, Hb(W) and n.In both equations Hb(W) represents the enthalpic effect of the hydrophobic solute in pure water. Because it is derived from measurements over the whole concentration range it contains moreM. BOOIJ AND G. SOMSEN 14 12 2857 I I I - - 14 - - 12 - FIG. 2.-Enthalpies oftransfer from water (W) to DMF +water mixtures (M) relative to those of glycine-HBr for a number of amino-acid hydrobromides at 298.15 K: 0, alanine-HBr; x ,2-aminobutyric acid-HBr; 0, valine-HBr; D, isoleucine-HBr; A, 4-aminobutyric acid-HBr. TABLE THE ENTHALPIC EFFECT Hb(W) OF THE HYDROPHOBIC HYDRATION, THE PARAMETER n, WHICH IS A MEASURE OF THE NUMBER OF WATER MOLECULES IN THE HYDRATION CAGE, AND THE MEAN DEVIATION 6 BETWEEN THE VALUE OF A(dH*) CALCULATED WITH THESE PARAMETERS AND THE EXPERIMENTAL VALUES FOR THE SIDE CHAINS OF SOME AMINO-ACID HYDROBROMIDES AND OF CORRESPONDING PRIMARY ALCOHOLS~~ IN DMF +WATER MIXTURES AT 298.15 K H b W ) 6 /kJ mol-l n /kJ mol-l H W ) 6 /kJ mol-l n /kJ mol-l ala -0.8 (18.0) 0.16 C2H50H - 5.5 5.9 0.08 Val -7.1 7.6 0.26 (CH,),CHCH,OH - 10.7 9.4 0.28 leu - 8.4 11.6 0.24 ile - 7.7 12.9 0.35 2-aba -4.1 (9.9) 0.14 n-C,H,OH - 8.4 8.1 0.12 norval -7.4 9.8 0.24 n-C,H,OH -10.0 11.0 0.21 - - - - - - - - - - - - n-C5Hl,0H -11.4 13.0 0.3 1 information than AH&?(DMF --+ W).Originally the parameter n was considered to be equal to the number of water molecules forming a clathrate-like cage around one alkyl group. Recently,2 it was shown that the value of n is not unambiguously defined by the model. However, trends in n are significant.2858 HYDROPHOBICITY OF AMINO-ACID MOLECULES Computer fits of our data to eqn (4) gave good agreement between calculated and experimental data, as judged from the mean deviation 6 between them (see table 3).Also shown in table 3 are values of Hb(W) and n for a number of alcohols. These were obtained by subtraction of AHgl of methanol from AHgl of the other alcohols18 for each X , and fitting the values of A(AHgJ defined in this way to eqn (4). From the results we conclude that Hb(W) provides a better distinction with regard to the hydrophobic properties as a function of the length of the alkyl chain than the transfer quantities : the differences between the valine salts with 2-aminobutyric acid-HBr on one hand and the leucine salts on the other are larger for Hb(W) than for A(AHtF).Fig. 2 illustrates this: the main differences between valine-HBr and isoleucine-HBr do not lie in the difference of their properties in pure DMF and pure water, but in the mole fraction range where the maximum in AHgl occurs. In terms of the clathrate model this means that upon addition of cosolvent the water-clathrate structure breaks up more readily around an isopropyl group than around a branched butyl chain. IF I I I I I I / + - Y- I f C H Me Et Pr Bu FIG. 3.-Enthalpic effect Hb(W) of the hydrophobic hydration plotted against the number of carbon atoms in the side chain: 0, amino-acid hydrobromides in DMF+water; x , n-alcohols in DMF+water;I8 +, amino acids in ethanol + water.8 In fig. 3 Hb(W) is plotted as a function of the number of carbon atoms in the side chain, n,.Note that the line for the amino-acid hydrobromides from Me on runs virtually parallel to that for the n-alcohols. Apparently the influence of the functional group on the clathrate does not stretch further than the first carbon atom in the side chain. Consequently, the CH,-group increments for Hb(W) appear to be independent of the functional group in the molecule. This conclusion is not substantiated by results of a similar analysis for amino-acid side chains in ethanol + water mixtures based on literature datas for the solubility S of amino acids at different temperatures by means of the approximation AH,,, = - Rd In S/d( 1 / T ) . Although the result (see table 4) givesM. BOOIJ AND G . SOMSEN 2859 the same trend as we found, fig.3 shows that the dependence of Hb(W) on n, does not run parallel with those for our compounds or for the alcohols. We assume that this discrepancy is related to the hydrogen-bonding ability of the cosolvent ethanol in contrast to the relative inertness of aprotic DMF. TABLE 4.-THERMODYNAMIC PARAMETERS OF AMINO-ACID SIDE CHAINS DERIVED FROM SOLUBILITY DATA hydrophobicity parameter /kJ mol-l na /kJ mol-' /kJ mol-l Hb(W)a 6" A(AGt9 ala - 2.6 4.3 0.08 2.1b 3.2f 2-aba Val - 11.9 2.7 0.18 6 . 4 6 7.4-f leu - 12.5 7.3 0 . 0 4 7Sd 8.7f - - - - 12.8f ile norleu - - 10.9" - - 5.OC - - - - a See table 3; ref. (5), ethanol; estimated from data in ref. (19) with the procedure ref. (5), average of values of ref. (5); from ethanol, butanol and acetone; f ref.(6), in most cases adapted from ref. (5). ref. (5), average of values from dioxan and ethanol; In table 4 we have also listed the hydrophobicity scales proposed by Nozaki and Tanford5 and by Jones.6 These are based on the Gibbs energy of transfer A(AGtF) from a non-aqueous solvent to water. For the limited amount of data that allow comparison, trends in the absolute values of Hb(W) are very similar to those in A(AGt$+). The similarity of the numbers for - Hb(W) and A(AG,?) should be regarded as coincidental. The calculated values for n given in table 3 only show the regular increase with the chain length for the valines and the leucines. No significance should be attached to the values of n for alanine-HBr and 2-aminobutyric acid-HBr as the magnitudes of the deviations from linearity of A(AHgl) as a function of X, are small.Indeed, as was found for the comparable alcohols,ls n for norvaline-HBr, which carries a straight propyl group, is larger than n for valine-HBr, which has a branched propyl group. Possibly the larger value of n for isoleucine-HBr than for leucine-HBr reflects the more ' straight-chain ' character of the former. The solid lines in fig. 2 represent the calculated curves according to eqn (5). Deviations from the measured points indicate the approximate nature of the model. The exponent n is largely determined by the mole fraction of water where the curve deviates from linearity: the higher this X, is, the larger n is. In all cases except 4-aminobutyric acid it seems that the model underestimates n because observed points around X, = 0.85 lie above the calculated curve.On the other hand, the experimental values at X , = 0.95 lie below the curve. An explanation for this last discrepancy could be that addition of a few percent of DMF to water does not destroy clathrate structures to the extent assumed in the model. For example, when the model is extended to allow two cosolvent molecules to break up the clathrate, better fits at X, = 0.85 and 0.95 are obtained. Hb(W) changes only little, while n assumes values between 20 and 30 in this adapted model. Some deviations also occur at low X,, although they are only slightly larger than the experimental uncertainty and probably are related to a difference in association2860 HY DROP HOB1 CI TY OF A MI NO-AC ID MOLECULES to ion-pairs between compounds with longer side chains and glycine (see also the footnote in table 2), whereas an association correction (see above) was only applied to measurements in pure DMF.F. Franks, in Water, A Comprehensive Treatise, ed. F. Franks (Plenum Press, New York, 1975), vol. 4, chap. 1. W. J. M. Heuvelsland, M. Bloemendal, C. de Visser and G. Somsen, J . Phys. Chem., 1980,84,2391 and references therein. G. D. Rose and S. Roy, Proc. Natl Acad. Sci. USA, 1980, 77,4623; M. Kanehisa and T. Y. Tsong, Biopolymers, 1980, 19, 1617; P. Y. Chou and G. D. Fasman, Adv. Enzymol., 1978, 47, 45. R. Akeroyd, J. A. Lenstra, J. Westerman, G. Vriend, K. A. Wirtz and L. L. M. van Deenen, Eur. J . Biochem., 1982, 121, 391. Y. Nozaki and C. Tanford, J . Biol. Chem., 1971, 246, 221 1. D. D. Jones, J. Theor. Biol., 1975, 50, 167. ' C. H. Spink and M. Auker, J. Phys. Chem., 1970,74, 1742. M. S. Dunn and F. J. Ross, J. Biol. Chem., 1938, 125, 309. A. C. Rouw and G. Somsen, J . Solution Chem., 1981, 10, 533. lo W. J. M. Heuvelsland, C. de Visser and G. Somsen, J. Phys. Chem., 1978, 82, 29. 'l W. S. Frost, J. Am. Chem. Soc., 1942, 64, 1286. l2 A. E. Martell and R. M. Smith, Critical Stability Constants (Plenum Press, New York, 1974), vol. 1. l3 E. J. King, in Physical Chemistry of Organic Solvent Systems, ed. A. K. Covington and T. Dickinson I4 P. G. Sears, R. K. Wolford and L. R. Dawson, J. Electrochem. Soc., 1956, 103, 633. l 5 C. de Visser and G. Somsen, Reel Trau. Chim. Pays-Bas, 1972, 91, 942. l6 H. S. Harned and B. B. Owen, The Physical Chemistry of Electrolytic Solutions (American Chemical l7 R. P. Held and C. M. Criss, J. Phys. Chem., 1967, 71, 2487. la A. C. Rouw and G. Somsen, J. Chem. Thermodyn., 1981, 13, 67. l9 J. P. Greenstein and M. Winitz, The Chemistry of the Amino Acids (Wiley, New York, 1961), vol. (Plenum Press, New York, 1973), p. 402. Society, Washington, 3rd edn, 1958). 1, table 5-12. (PAPER 2/274)

ISSN:0300-9599    

DOI:10.1039/F19827802851

出版商:RSC    

年代:1982

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1982, 78, 2861-2864 Thermodynamics of Oligomeric Alkane Liquid Mixtures at High Pressures BY ERIC DICKINSON Procter Department of Food Science, University of Leeds, Leeds LS2 9JT Received 16th February, 1982 For binary liquid mixtures of n-alkanes, the previously reported changes in sign and magnitude of the experimental excess volume with increasing pressure are found to be consistent with the phenomenological theory of corresponding states. In describing the thermodynamic state of a liquid mixture of volume V at pressure p and temperature T, we say that the applied pressure is high if it is comparable to or greater than the ‘internal pressure’ T(ap/a T)v. Typically, T(ap/aT), takes a value of ca. 2 kbar, and therefore experiments done at atmospheric pressure (ca.1 bar) occur at effectively negligible external pressure. As recognized by Bridgman,l experimental behaviour at low or negligible pressure is a poor guide to what is likely to happen at high pressure. For binary liquid mixtures of n-alkanes at ambient pressure, the reported excess volumes are invariably negative.2 The magnitude of the volume change increases with (a) the temperature and ( b ) the difference in chain length of the pure-component molecules. This behaviour can be understood in terms of the principle of corresponding states as applied to mixtures of oligomers by Prig~gine.~ With oligomers belonging to the same homologous series, the negative sign of the excess volume is the direct consequence of the form of the reduced equation of state, and the magnitude of the excess volume is related in a simple way to the difference in the reduced temperatures of the pure component^.^ Positive volume changes are observed experimentally at atmospheric pressure,2 but only with mixtures of oligomers that are chemically different.In non-polar examples of this latter type (e.g. n-alkane + linear dimethyl- siloxane), the positive excess volume is attributed5 to the unequal pressure reduction factors of the two components. In a recent experimental study of several binary mixtures of n-alkanes at pressures up to 5 kbar, Dymond et aZ.6$7 found that the magnitude of the excess volume decreases with increasing applied pressure. Most interestingly, however, they report that the excess volume eventually becomes positive so long as the temperature and pressure are high enough.It is the purpose of this short paper to examine whether these new high-pressure data are consistent with the corresponding-states theory for mixtures of homologues. We shall not be concerned here with any anomalies that arise from proximity to critical points. According to the phenome_nological formulation of the principle of corresponding states,6 the reduced volume 6 of a pure o1igomeric)iquid i of molar volume Vm, is a universal function of the reduced temperature = T/T,* and reduced pressure pi = p/p,* : q = vm, i/ vg = Q P i , Q. (1) 286 12862 OLIGOMERIC ALKANE LIQUID MIXTURES The reduction factors V f , Tf andpf for a given homologous series depend only on the chain length n. For a mixture of molar volume V,, eqn (1) may be rewritten as (2) where (0 = T / ( T*) is the reduced temperature of the mixture, ( p " ) = p/( p*) is the reduced pressure of the mixture, and ( V * ) , ( T * ) and ( p * ) are average volume, temperature and pressure reduction factors, respectively.The molar excess volume Vg of a binary mixture (i = 1, 2) at constant temperature and pressure is given by v = Vm/( V*) = V((P), ( F ) ) where x, is the mole fraction of component 1. The magnitude of the predicted exce_ss volume depends to a considerable extent on the rules for calculating ( p " ) and ( T ) from the pure-component reduced pressures and temperatures. For a mixture of chain molecules having uniform force fields and no special 'end effects', Patterson and ~ o w o r k e r s ~ ~ ~ ~ have argued that the reduced quantities for the mixture are given by (4) ( 5 ) (6) (7) (p")-' = 41 p"l'+4, p";' ( F ) = x, E+X, z.The volume fraction 4, in eqn (4) and the surface fraction X, in eqn (5) are defined 41 = x, V,*/(Xl V;" +x, V,*> Xl = XlP;" ~;"l(XlP,* v;" +X,P,* C). by The two fractions are equal if p,* = p;. sum of three contributions: For conceptual purposes, it is convenient to regard the excess volume as being a VZ = VE(1) + VE(I1) + VE(II1). (8) The quantity VE(1) is the notional contribution to V: from mixing the components at constant reduced pressure; VZ(I1) is the contribution from mixing at constant reduced temperature; and Vz(II1) is a cross-term. Whzn the p_ure-com_ponent_reduced temperatures are not too dissimila_r, we_may expand V(( p"), q) _and V(( p"), T,) about p(( p"), ( F ) ) in powers of AT = q- T,.To second order in AT, VE(1) then has the form VZ(1) = -(x, X2 V,* - X, Xl V,*) AT'(aV/a( F))(;) -$(x, Xi V,* + X, V,*) (AT), (a2 V/a( T)')(;). (9) At atmospheric pressure, when mixing occurs at essentially constant reduced pressure, VE(1) is the only contribution that need be ~onsidered.~ At high pressures, when p";' a_nd p';l_are not too dissiFilar, it is ctnvenient, because of the form of eqn (4), to expand V(p",, ( T ) ) and r(P,, ( T ) ) about V(( p'), ( T ) ) in powers of A(p"-l) = p"il - fi;'. To second order in A(p"-l) we have vg(11) = -$(x, 4; v;" + X, 4: v;) [~(p"-1)]2 (aV/a( p"-y)(n. (10) We note that the expansion in A(p"-l) is not valid at low pressure,At high pressure, the final term Vz(II1) in eqn (8) involves the product of AT[A(p"-l)] and the cross-derivative (a2 p/a( na( 8-l)).It is clear from eqn (8)-(10) that a detailed knowledge of the reference equation of state is needed for the calculation of excess volumes at finite reduced pressures, andE. DICKINSON 2863 that the scarcity of precise pure-component equation-of-state data is the main limitation on quantitative prediction. We prefer to concentrate here on qualitative and semi-quantitative aspects, Of particular interest is the simple expression for VE obtained if p: = p ; : (1 1) This assumption of equal pressure reduction factors has been shown4 to be valid for a mixture of two n-alkanes. According to eqn (lJ), th_e sign and magnitude of Vg are determined by the sign and magnitude of (a2V/a( T)')(z), which in turn depend on the curvature of V as a function of T for the conformal reference fluid at constant pressure.It is well known that, at low pressures, the isobaric expansivity ap = (l/V)(aV/aT), of a pure liquid increases as the temperature rises [(a2 V/aT2)p > 01 and ultimately diverges at the gas-liquid critical point. What is less widely known is that at high pressures the sign of (a2V/8T2), is reversed. According to Bridgman,l the first trace of this phenomenon was seen by Amagatll near the upper end of his pressure range (ca. 3 kbar), but apparently the effect seemed to Amagat so unlikely that he ascribed it to experimental error! With measurements up to higher pressures, Bridgman and many others have conclusively demonstrated the reality of the effect.Recalling the thermodynamic identity involving the heat capacity C , V g = -]i(~, & V: +x, & V,*) (AT)' (a'V/a( T)')(i;l) + (acP/aP)T = - T ( P v / ~ T ~ ) , (12) Bridgman notes' that 'this reversal in the sign of (i32V/i3T2)p is obviously a most important point for any theory of liquids'. f a C I - T+ FIG. 1.-Variation in the derivativ: of reduced volume P with respect to reduced temperature F. The quantity dP/dF is plotted against T for three fixed and widely separated values of the reduced pressure: (A) low reduced pressure ( p - 0), (B) intermediate reduced pressure [ p - T(dp/W),], (C) extremely high reduced pressure [ p B T(i3p/dT),]. In fig. 1 the form of (aV/aF)$ as a function of for a real liquid is shown schematicall1 fo_r low, intermediate and high-reduced pressures.At low reduced pressures (a V/aT),- is an increasing function of T, and so V g from eqn (1 1) is ne_gacve at all temperatures. On the other hand, at extremzly high reduced pressures (a V/aT)$ is a slow, monotonically decreasing function of T, and V z from eqn (1 1) is small and positive at all temperatures. At intermediate reduced pressures (well away from the critical point), the predicted excess volume is sm_all in magnitude, and its sign may be positive or_negative depending on whether (a V/tlT)i3 is a decreasing or increasing function of T. That is, at intermediate pressures, the corresponding-states theory predicts that V: is negative at high temperatures and positive at low temperatures.2864 OLIGOMERIC ALKANE L I Q U I D MIXTURES To get an idea of the pressure at which the predicted excess volume changes sign, let us consider the system n-hexane( 1) + n-hexadecane(2).It is convenient to choose n-undecane as the conformal reference substance because its chain length [n = $(6 + 16)] is such that the reduced temperature of the reference substance is almost exactly _equal to that of the equimolar mixture (4, = 0.29). The second derivative (d2v/dT2) at constant pressure is related to the expansivity ap by (13) Based on specific-volume data12 for n-undecane in the temperature range 303-573 K and the pressure range 0-5 kbar, fig. 2 shows a plot of a; against pressure at 373 K. The same graph shows experimental values of V z for an equimolar mixture of n-hexane + n-hexadecane at 373 K over the same pressure range? The strong corre- lation between the sign and relative magnitude of V$ and the sign and relative magnitude of a; confirms the semi-quantitative validity of eqn (1 1) for n-alkane (da,/dT)+a; = a’p = ( PT*2)-1(d2V/dT2). mixtures.-1 0 I I I I 0.5 0 - d ; -1.0 L. -0.5 cI \ WE -1.5 0 1 2 3 4 PlkbW FIG. 2.-Correlation between the function a; [defined in eqn (13)] for n-undecane [ref. (12)] and the equimolar excess volume V g for n-hexane+n-hexadecane [ref. (6)]. The quantities a; and V g at 373 K are plotted against the pressure p . As a final comment on eqn (ll), we note that when (a2P/3(p)2)(gJ is smalljn magnitude it may change in sign across the composition range. This is becau2e ( T ) is itself a function of composition [eqn (5)]; and it could so happen that <iY-v/a( T)2),5> is negative at low values of x, and positive at high values Qf x,.For n-hexane+n- hexadecane at intermediate pressures, this would imply a predicted negative excess volume at high mole fractions of n-hexane and a positive one at low mole fractions. Indeed, such S-shaped V$ against x, curves are found6 experimentally at 3 1 kbar. P. W. Bridgman, The Physics of High Pressures (Bell and Sons, London, 1949), chap. 5. Y. P. Handa and G. C. Benson, Fluid Phase Equilibria, 1979, 3, 185. I. Prigogine, The Molecular Theory of Solutions (North-Holland, Amsterdam, 1957), chap. 16. E. Dickinson and I. A. McLure, J. Chem. SOC., Faraday Trans. I, 1974, 70, 2328. J. H. Dymond, K. J. Young and J. D. Isdale, J . Chem. Thermodyn., 1979, 11, 887. ’ J. H. Dymond, J. Robertson and J. D. Isdale, J. Chem. Thermodyn., 1982, 14, 51. J. Hijmans, Physica, 196 1, 27, 433: S. N . Bhattacharyya, D. Patterson and T. Somcynsky, Physica, 1964, 30, 1276. * D. Patterson and J. M. Bardin, Trans. Faraday SOC., 1970, 66, 321. lo D. Patterson and G. Delmas, Trans. Faraday SOC., 1969, 65, 708. l1 E. H. Amagat, Ann. Chim. Phys., 1893, 29, 68. l2 A. K. Doolittle, J. Chem. Eng. Data, 1964, 9, 275. (PAPER 2/285)

ISSN:0300-9599    

DOI:10.1039/F19827802861

出版商:RSC    

年代:1982

数据来源: RSC

摘要:

Reviews of Books Physical Chemistry. By J. R. BROMBERG. (Allyn & Bacon, Boston, 1980.) Pp. xiv+882. Price €9.95. During the past decade or so, a large number of text books on Physical Chemistry have appeared; this is a sure sign that a really satisfactory one does not yet exist. There are in principle two possible extreme types of such books, perhaps best exemplified by the two famous ones of the late 1940s and early 1950s, viz. Glasstone’s Textbook and Hinshelwood’s Structure of Physical Chemistry. The former attempted to cover the entire field required by an honours student. It was rightly criticised for some lack of perspective and its preoccupation with detail to the detriment of presenting a unified whole. Nevertheless, this reviewer believes it to have been a good book for its time (and we all used it).In the latter book, Hinshelwood painted a complete picture where perspective was crucial and the interrelationships between sections of the subject were clearly identified. It was a superb book to read after Glasstone, but one would hardly have recommended it to a student as a standard text (nor indeed would the author have wished this). Most texts published since these two have attempted, predominantly, to replace Glasstone rather than Hinshelwood. But Physical Chemistry has continued to grow and so too has what we expect students to know of it. Thus texts have tended to contain more and in a more compressed form. Nevertheless some authors have attempted to show a thread running through the subject and present some sort of ‘whole’.The present book by J. P. Bromberg moves a little in this direction. In just under 900 pages it is not now possible to cover Physical Chemistry in an exhaustive way. Either much must be left out or the treatment must be excessively brief or superficial or a combination of these. The author has elected to leave some things out but not many. In other cases the treatment tends to be sketchy to the point where perhaps they were better not mentioned at all. The treatment of Thermodynamics has a slightly old fashioned look (Carnot cycles and the odd piston) but is reasonably comprehensive and the student who does the problems will have learnt enough thermodynamics and be able to do relevant calculations. Indeed throughout the book there are numerous problems of greatly varying degrees of difficulty (any student who did half of them would know a great deal of Physical Chemistry and sail through most finals papers), a few are rather poorfy defined but many are excellent and some unusual.It would have helped to have had answers. Thermodynamics is followed by a discussion of the ‘ Statistical Approach. ’ including the Maxwell-Boltzmann distribution of velocities, transport properties of gases and finally Statistical Mechanics. Nearly a quarter of the book is devoted to the Quantum Mechanics of Atoms and Molecules and then a substantial section on Solids. The final section representing appreciably less than 10% of the complete work is on Chemical Kinetics and is the poorest part of the book. While we all have biases, 8 pages on the Ultracentrifuge, compared with 2 on Collision Theory or 7 on Activated Complex Theory (including potential energy surfaces) or 4 on Unimolecular Reactions does not seem a reasonable division.Throughout there are many diagrams and drawings which are uniformly well done (only one with an error was noted) and the text has a most pleasing appearance. In addition, there are thumb-nail biographies of many famous scientists which certainly add interest to the volume. The book represents value for money and can be recommended to the average to good student (especially if he can be persuaded to do the problems), the really good student will do better with Atkins. Having said that, if funds are not too limiting maybe the real advice is to get separate books on the main branches of Physical Chemistry and having perused them end up by reading Hinshelwood, which though dated and containing many errors, does show one how the pieces fit together. H.M. FREY Received 7th January, 1982 28652866 REVIEWS OF BOOKS Dielectric Properties of Binary Solutions. A Data Handbook. By Y. Y. AKHADOV. (Pergamon Press, Oxford, 1981.) Pp vi+475. Price E47.00, $1 12.50. A compendium of experimental data has certain attractions for a Physical Chemist and the volume at present under review will probably prove to be no exception to this generalisation. The original compilation evidently summarised the literature up to 1972 but an additional chapter (chap. V) has been added with its own bibliography and index which extends the survey from 1973 up to 1979.In chap. 1 the author has followed the precedent set by F. Buckley and A. A. Maryott in their compilation of dielectric dispersion data of 1958, by summarising the various numerical relationships and theoretical equations used in the literature to represent or interpret experi- mental data. The information incorporated in subsequent chapters includes values of permittivity measured at a single frequency (usually sufficiently low for these to approximate to the static values) as a function of both composition and temperature. These results are then followed by data for the real and imaginary permittivities of binary mixtures made over the range of frequency appropriate to the dispersion. Where the authors of the original papers have chosen to present their experimental results graphically, this format has been retained in chap.IV. In a few cases, the frequency dependence of the complex permittivity has been represented by the values of the parameters derived from one or other of the standard expressions given in chap. 1, but this is by no means universally employed even when this information has been provided in the original paper. No attempt has been made to assess the reliability or precision of the data sum.marised or to assign limits of accuracy to any derived parameters. The Russian origin of this text is betrayed by the appearance of the Cyrillic script in a number of places, e.g. on p. 71, 196 and elsewhere. In addition there are many other trivial typographic errors including the misspelling of the names of several authors.Fortunately these inaccuracies do not appear to extend to the references themselves. However, for a book of this price, greater care in the preparation of the text might reasonably have been expected. Perhaps the most serious criticisms involve the omission of any reference to the units employed particularly when various thermodynamic parameters of activation are being quoted, for example the values of AFand AHgiven on p. 230,324 and elsewhere. Another objectionable feature is the use of 10-l2 z or even .r/1012 (p. 241) when 1OI2 t should clearly be used in the headings of tables of dielectric relaxation times. This applies even when the correct representation has been used in the original paper. A similar criticism can also be made of some tabular values of tan 6 and molarity.Nevertheless the comprehensive coverage of the literature, which is the most impressive feature of this book, more than compefiates for these minor errors. E. A. S. CAVELL Received 17th December, 1981 Principles of Polymer Morphology. By D. C. BASSETT. (Cambridge University Press, 1981 .) Pp. ix+251. Price 625 (€8.95 p/back). This is a considerable book, with detailed coverage and a range of micrographs and diagrams which belie its size if not its price. The text tells two tales. On one hand, it presents the principles of crystalline polymer morphology as a logical sequence which will commend the book not only to the general reader, but also as a student text for suitably advanced courses. On the other, it measures the author’s dedication to the subject over two decades and cannot but help underline his signal contributions.It is fitting that a new method of sample preparation, developed in his Reading laboratory, has opened up fresh horizons for the subject and made possible many of the beautiful micrographs which are such a feature of the book. As perhaps the title might suggest, the emphasis is on structures which can be seen in the microscope, and the author restricts himself to ‘crystalline’ as opposed to non-crystalline or liquid-crystalline polymers. After the introduction, in which due respect is paid to the principles of molecular conformation, the text proper opens with a treatment of spherulitic morphology which is set in the context of Keith and Padden’s 1963 theory.Chap. 3 is an authoritative account of the structure of polyethylene single crystals grown from solution. Chap. 4 develops the same themeREVIEWS OF BOOKS 2867 to include pyramidal habits and twinning, but in addition considers growth of aggregates of single crystals of a range of different polymers. It also introduces the reader to a remarkable series of micrographs of lamellae in melt crystallised polyethylene. The treatment in the next chapter of the effects of annealing on the crystal structures, draws much more heavily on microscopic evidence than the available diffraction information. A topic which is both current and contentious presents a problem to any author. He has either to appear to ignore issues just when they seem to be on everyone’s lips, or to attempt to construct a path amongst the arguments while they are yet changing.Dr. Bassett takes the first course in his treatment of crystallization theories. He presents the picture much as it stood in the mid 70s, and tacitly avoids dwelling on the impact of recent ideas of Flory and others, or of new experimental approaches such as neutron diffraction. Nevertheless chap. 6 is a clear statement of the longer-established theories with just the right amount of detail. Chap. 7 is memorable for the author’s account of high pressure (or anarbaric as he calls it) crystallization, which in a commendably concise way summarises and updates his earlier review of the subject. It also covers the area of strain-induced crystallization and includes ‘ shish-kebabs’ and row-nucleated morphologies.The remainder of the book is given over to a description of degradation, concentrating mainly on polyethylene and its response to both chemical attack and radiation, and selected aspects of mechanical behaviour which are of particular morphological interest. These latter, which form the final chapter, include crystal deformation processes such as slip, twinning and stress-induced martensite, as well as Hay and Keller’s in situ observations of drawing spherulites. The book is well assembled with adequate reproduction of the many telling micrographs. At some points the text reads more easily than at others, but it is never confused. ‘Principles of Polymer Morphology’ fills an important gap on the polymer bookshelf. It is welcome indeed ! A.H. WINDLE Received 7th January, 1982 Maintaining and Troubleshooting HPLC Systems: A User’s Guide. By D. J. RUNSER. (Wiley- Within its hundred and sixty-three pages, this book is a mine of detailed, practical information on how to operate, maintain and troubleshoot h.p.1.c. equipment. It neatly fills the gap between general books on the theory and practice of high performance liquid chromatography and the manuals of equipment manufacturers. Wisely, however, the author avoids drawing too sharp a boundary between his topic and other aspects of practice because preventive maintenance is very much a matter of proper operation in the first place. Thus, the chapter on maintaining and avoiding problems with pumps necessarily involves detailed descriptions of the different types of pump and their characteristics.For the choice of mobile phase to achieve a desired separation the reader is referred elsewhere but there are other aspects of this choice which bear on trouble-free operation of the system and these are fully covered. Similarly there is a useful short section on column selection, based on the chemistry of the sample. Included is a chapter on laboratory safety for h.p.l.c, a detailed troubleshooting guide, instructions for calibrating a laboratory strip chart recorder, and a checklist of what to do before calling the service representative. The writing is direct and concise so that one can forgive some infelicities of style and ambiguities of meaning. Occasionally points are alluded to tersely where a few more words of explanation would have been welcome.The book is well produced, indexed and referenced. It should provide a valuable guide for the user of h.1.p.c. who already has a general or theoretical knowledge of the subject and it is well suited to desk reference or use at the laboratory bench. J. R. CONDER Received 26th January, 1982 Interscience, Chichester, 1981.) Pp. xiii+ 163. Price f 17.65.2868 REVIEWS OF BOOKS Nonaqueous Solution Chemistry. By 0. POPOVYCH and R. P. T. TOMKINS. (Wiley-Interscience, New York, 1981.) Pp. xiv+500. Price E36.75. Described as a concise compendium of information on the chemistry of non-aqueous solvent systems, this book, according to the fly-leaf, aims at bringing together widely scattered and often over-specialised literature into a coherent presentation that explains and evaluates the approaches to ion-ion and ion-solvent interactions, acid-base equilibria and mechanisms of chemical and electrochemical reactions in non-aqueous solvents.In fact it ably summarizes information drawn largely from the five or six key monographs published between 1966 and 1976. There is a notable lack of reference to primary publications and even reviews from the last five years. After a very short introduction, chap. 2 (26 pp.) deals with solvent-solute interactions and is followed by a review of the general characteristics and classification of nonaqueous solvents (44 pp.). Chap. 4 (89 pp.) is devoted to thermodynamic properties and there follow discussions of the first author’s specialities, thermodynamic transfer functions (36 pp.) and acid-base equilibria (53 pp.).Spectroscopy (chap. 8, 55 pp.) is sandwiched by the second author’s special interests in transport properties (59 pp.) and electrode processes (51 pp.). The chosen coverage and particularly the illustrative spectra for chap. 8 betray the lack of direct experience of the authors in this area. For example, the omission of reference to distinguished recent contributions from Popov, Hertz and Laszlo, to mention only three of those who have used n.m.r. spectroscopy with conspicuous success, constitutes a real weakness. The rates and mechanisms of chemical reactions are discussed in chap. 10 (45 pp.) and the final chapter includes three essays on applications of nonaqueous solvents to hydrometallurgy, metal electrodeposition and batteries (27 pp.). Ths book is essential reading for any graduate student starting research with non-aqueous solvents and certain chapters should be useful to the final honours undergraduate.It is a better book than Gordon’s strangely named ‘ The Organic Chemistry of Electrolyte Solutions’ (1975) from the same stable. The standard of typesetting and illustration production, as expected from this publishing house, is excellent. Strongly recommended for all libraries and well filled pockets. A. K. COVINGTON Received 7th January, 1982 Membrane Filtration. Applications, Techniques and Problems. Ed. by B. J. DUTKA. (Marcel This book is a review of the developments and uses of membrane filters in water microbiology. As such it is, quite correctly, a detailed and specialist work concerned with only a very restricted subject area.The individual chapters are factual and give, in often considerable practical detail, information on materials, methods and techniques employed in the various applications of membrane filtration in the systems under consideration. In this sense the book’s principal use will be as a practical manual rather than as a theoretical text. The book has twenty-one chapters over 612 pages (including a brief Subject Index) in camera-ready type. The material is well laid-out and presented, with reasonable use of diagrams and illustrations; it does not suffer from the fragmentary nature and loose organisation of so many of the post-symposium volumes similarly published in this format.The contributors are mainly from the United States and Canada, with ‘local’ statements from the U.K., South America, Japan, South Africa and New Zealand. While the primary focus of the material presented is water quality and public health, some consideration is also given to stress injury and recovery, ecological studies and industrial applications. The book will be of value to microbiologists in general, and to environmentalists, engineers, and civic and industrial authorities concerned with resource management and water quality assessment. The first two chapters deal with the development of membrane filtration and its utilisation since 1957 in the United States for microbiological analysis of potable water supplies. The matter of membrane and pore ultra-structure is raised and the need for standardisation stressed.This question of standardisation is brought forward also by several other contributors, with regard to both microbiological methods and the choice of filter used. Dekker, New York, 1981.) Pp. xi+612. Price Sfr 185.REVIEWS OF BOOKS 2869 The following eight chapters consider the problems associated with microbiological identi- fication and enumeration, the use of indicator organisms, the direct examination of specific pathogens, and the application of membrane filtration to studies of fungi and virus, this last group being studied with the aid of the concentrating effect arising from the adsorption of the virus particles on the filter. Five chapters are then devoted to the application and use of membrane filtration in water analysis in other geographical locations throughout the world.Here it is fascinating to observe the tangled web arising from EEC-inspired legislation, and to note that in Japan with its many short, cold and comparatively clean rivers the chief problems arise from industrial pollution with consequently biological and chemical oxygen demand being more important than colifonn counts. The remaining six chapters deal with individual items including studies of injury and recovery from environmental stress, and the development of a new hydrophobic grid membrane filter allowing very considerably increased recovery and accuracy in enumeration. The significance is stressed of these matters to the quantitative assessment of microbiological analyses and the conclusions that are drawn from them.Altogether this book constitutes a timely and authoritative statement on an important technology which is now well established, and is likely to develop further in its own and in related fields. W. A. HAMILTON Received 7th January, 1982 Structural Order in Polymers. Ed. by F. CIARDELLI and P. GIUSTI. (Pergamon Press, Oxford, 1981.) Pp. xiv+247. Price E30. This book is the collected principal lectures delivered at an IUPAC conference held in Florence in September, 1980, to commemorate twenty-five years of stereospecific polymerization and dedicated to the memory of Prof. G. Natta. It contains sixteen articles mostly of CQ. 10000 words or fewer, by distinguished authors, which between them touch on most aspects of the very broad general title.They are arranged in three groups. The first group of six articles is devoted to the stereospecific polymerization of olefins and diolefins. Flory leads with consid- eration of chain configurations and crystallinity and is followed by Wilks on the fascinating history of the development of stereospecific polymerization. Corradini deals with the crystallo- graphic characterization of molecular and crystal structures while reaction mechanisms are discussed by Yermakov (for polypropylene) and Porri (dienes). Isotactic polypropylene is one of the principal commercial successes of stereospecific polymerization and its development over the quarter-century is reviewed by Galli. There are a further six lectures on the wider themes of constitutional and configurational order in synthetic and bio-polymers.Two of these are devoted to molecular order: heterogeneity in lactam polymers (Sebenda) and the synthesis of sequence-defined polynucleotides (Caru- thers). Much the longest article is that by Keller, on morphology and structure research in solid polymers. He shows how complementary use of many investigative techniques is now giving fine detail of how molecules and lamellae actually are organised in the bulk, for both synthetic and biological macromolecules. Globular proteins are discussed by Liquori, macromolecules in liquid crystal solvents by deGennes and Veyssie and there is an account of work on polymer blends from Stein’s laboratory. The final group of four articles has the theme ‘Polymers tailored to Specific Purposes’ and a biological emphasis.Lyman discusses the background to a successful synthetic polymer prosthesis for repairing small diameter blood vessels. There is a report from Smets’ laboratory on the influence of polymer matrices on photochemical reactions while immobilised enzymes and cells is Mosbach’s subject. Finally, Stannett considers the structure and performance of synthetic membrances. This conference report seems to me to be good of its kind with two particular merits. First, it has achieved good coverage across a very wide and important area which is fundamental to understanding much of polymeric behaviour. Secondly, not only are the articles authoritative, they are almost always succinct and commendably clear. There is no stale repetition of old2870 REVIEWS OF BOOKS material.On the contrary, the authors appear collectively to have achieved the ideal of being able to attract a reader’s attention beyond a specific interest into wider areas and then hold it. It would be an unfortunate reader who did not profit from perusing this volume. D. C. BASSETT Received 8th January, 1982 The Combustion of Organic Polymers. By C. F. CULLIS and M. M. HIRSCHLER. (Clarendon Press: Oxford University Press, Oxford, 1981.) Pp. xf419. Price €37.50. According to an interview reported in Chemical and Engineering News, Lord Todd, President of the Royal Society, believes that chemistry has had its biggest impact on society through the development of the products of polymerization reactions. Many polymers are used in forms which have a very high surface/volume ratio and, since they are mostly flammable, there may be a significant fire hazard in general use.Since combustion is a chemical reaction, there is a clear relationship between basic chemistry and the level of risk in practical applications; it is the object of the present volume to bring together these two aspects of the subject, and this it achieves most satisfactorily . The literature pertaining to the drastic effect of heat on polymers has, until very recently, consisted of three very different types of communication, none of them a text-book. There is very extensive coverage of the fundamental chemistry of degradation process brought about by heat in both the presence and absence of oxygen; secondly, there is the technological element, mostly in patents, on the treatment of textile fibres to render them non-flammable; finally, there are reports from and proceedings of symposia on combustion, flame retardancy and related topics.Two text-books have appeared recently, one by Aseeva and Zaikov, published in the U.S.S.R. in Russian, and one by Pal and Macskasy, published in Budapest in Hungarian. The former of these deals mainly with chemistry and the latter with testing methods so, in addition to the language barrier, neither has the breadth of the Cullis and Hirschler book. There are four distinct aspects of the present volume. Chap. 1 is background in the form of a review of the principal types of organic polymers; it includes highly relevant information regarding the main uses to which the materials are put.Chap. 2 discusses the hazards arising from polymer combustion, and reviews standard tests applied to plastic materials to determine the level of flammability. A particularly welcome feature here, and indeed throughout the book, is the truly international scope of the survey. As might be expected, the question of assessment of degrees of hazard brings the subject into the legal ambit, and the authors have included a section which compares the legal approach to questions of fire safety in various countries: even politics get a mention. Chap. 3 and 4 deal with the more chemical aspects of polymer combustion. Chap. 3 is an excellent review of the fundamental studies that have been carried out on the burning of polymers. Having made a distinction between degradation and decomposition, the authors present a review of the various stages of the combustion process, as revealed by studies of fundamental chemistry.The difficulty inherent in attempting to unravel the details of this complicated process is illustrated by the fact that there is still a lack of general agreement about the role of oxygen in the initial breakdown of hydrocarbon polymers. Part of this chapter contains discussions of the oxidative decomposition of individual polymers, and this is related to the Appendix, which is really a fifth chapter on the combustion behaviour of specific polymers. Chap. 4 discusses the chemistry of the reverse side of chap. 3, i.e. inhibition of corn bus tion. The references number some 1250 and include, inter alia, publications from Eastern Europe and Japan. As is usual with Oxford books, the text is beautifully printed and very well illustrated.In attempting to combine basic studies of oxidative degradation of polymers with the practical problems of fire hazards involved in applications of plastics, this book must be judged to have succeeded admirably. A. D. JENKINS Received 9th February, 1982REVIEWS OF BOOKS 287 1 Numerical Methods in the Study of Critical Phenomena. Ed. by J. DELLA DORA, J. DEMONGEOT and B. LACOLLE. (Springer-Verlag, Berlin, 198 1 .) Pp. ix + 267. Price DM60.00, $27.50. This book is Volume 9 in the Springer Series on Synergetics, and both it and the series need explanation. The word synergetics was coined by Hermann Haken of Stuttgart who, in 1975, wrote an article in Reviews of Modern Physics with the title ' Cooperative Phenomena in Systems farfrom Equilibrium'.On this he based his book of 1977, the first in the Springer series, which had the word Syrfergetics as its main title, and a sub-title of ' Non-equilibrium Phase Transitions and Self-organization in Physics, Chemistry and Biology '. The present book, which is a collection of some of the papers given at a conference in France in 1980, is loosely tied to these two themes, but has a title that is itself not very informative. The thirty papers cover a range of topics from pure mathematics, through physics, chemistry and biology to demography. Not one is on the familiar gas-liquid critical point, and few will help directly those who want to calculate the numerical values of critical indices or related properties.The transitions discussed, often obliquely, include gelation, spin-glass formation, the Kosterlitz-Thouless transition, the onset of oscillations in chemical reactions and the functioning of telephone networks : all-in-all, a book for the eclectic mathematician rather than the physical chemist. J. S. ROWLINSON Received 4th January, 1982 A.C.S. Symposium Series, no. 162. Photon, Electron and Ion Probes of Polymer Structure and Properties. Ed. by D. W. DWIGHT, T. J. FABISH and H. R. THOMAS. (American Chemical Society, Washington D.C., 198 1 .) Pp. xi + 442. Price $37. Camera-ready publications are often poorly prepared, do not present a balanced presentation of material and are poor value for money.This is not true of this publication which as the editors intended can be considered to be a benchmark for the state of current knowledge and future possibilities for the use of electron and ion probes of polymer structure and properties. It should, however, be added that the area of coverage of the text is not quite as broad as the title suggests. The interaction of photons with polymers is limited to high energy and is restricted to a consideration of far and vacuum ultraviolet and X-ray radiation. The book begins with a series of chapters which review the basic theory and methods associated with beam/specimen interactions, the nature of ionic and excited states produced and their transport in molecular solids. The topics covered range from gas-phase monomers to amorphous and crystalline polymers.This book is of particular interest to workers in the area of contact charging, chapters 3 and 4 presenting different theoretical approaches to the problem of charging and migration in insulators. The theoretical aspects of electron, photon and ion interaction are explored from a number of different viewpoints and this series of chapters constitute the bulk of this volume. The latter chapters are concerned with experimental studies and illustrate the topics developed theoretically in the introductory chapters. Topics included range from the now almost traditional techniques of ESCA-XPS to the newer methods of SIMS, resonant electron scattering and ETS. The book is the symposium report of the March 1980 Texas meeting of the American Chemical Society.A number of the contributions are dated March 1981 and appear to have been written as review papers rather than abstracts of papers presented. Certain of the chapters mention topics rather superficially, which in a comprehensive review treatise should ideally have been treated more thoroughly. However, such an expansion would probably have increased the cost and also delayed or inhibited publication. As with any conference proceedings, the volume lacks the coherence or unified presentation possible with the specially commissioned benchmark review work. However, the selection of material and quality of presentation is sufficiently high to make this contribution to the literature of value as a reference work for a number of years.At four pence a page and with a good subject index this is good value for money. The editors should be complimented on their efforts, and readers interested in electron and ion probe interactions of polymers should seriously consider adding this volume to their bookshelves and research libraries. R. A. PETHRICK Received 1st February, 19822872 REVIEWS OF BOOKS Studies in Modern Thermodynamics, Volume 3. Phase Theory. The Thermodynamics of Heterogeneous Equilibria. By H. A. J. OONK. (Elsevier, Amsterdam, 1981). Pp. xiv+269. Price Df1140.00, $59.50. There is no doubt that the Dutch have an enthusiasm for the Phase Rule that no other country can match. It appeared early, in the work of van der Waals, Kamerlingh Onnes and van Laar, reached its apogee in the five-volume treatise of Bakhuis Roozeboom and Schreinemakers, but is still strong in Zernike’s book of 1955, which is the best modern account of the field. Dr Oonk is another enthusiast in this tradition who has given us a highly personal view of the subject. He opens with four chapters that set out the conventional classical thermodynamics of the phase equilibria, although he ignores such modern developments as the use of fields and generalized densities, and the scaling of the free energy at critical and tricritical points. It then appears, however, that he has only one real aim in this book and that is the calculation of isobaric phase diagrams of binary systems from a knowledge of the excess Gibbs free energy, GE, as a function of temperature, T, and composition, x, and vice versa. The first calculation presents few problems, but the second is more difficult, since a phase diagram describes only a set of trajectories in a T, x-space, and so generally cannot give GE as a function of both variables without additional information or assumptions. He describes, with detailed examples, how this programme can be carried out. The book was written on a word-processor and the typography is exceedingly ugly. Moreover, the number of letters per page is so few that the book is even more expensive than it appears. J. S. ROWLINSON Received 19th January, 1982

ISSN:0300-9599    

DOI:10.1039/F19827802865

出版商:RSC    

年代:1982

数据来源: RSC