摘要:

QUARTERLY REVIEWS THE CHEMICAL SOCIETY PATRON HER MAJESTY THE QUEEN President SIR ALEXANDER TODD M.A. D.Sc. F.R.S. Vice-presidents who have filled the office of President 14. J. EhlELkUS C.B.E. M.A. D.Sc. SIR CHRISTOPHER INGOLD D.Sc. F.R.S. F.R.T.C. F.R.S. Sc.D. F.R.S. F.R.S. F.R.S. LL.D. F.R.S. SIR CYRIL HINSHLLM'OOD O.M. M.A. SIR ERIC RIDEAL M.B.E. M.A. D.Sc. E. L. HTRST C.B.E. D.Sc. LL.D. SIR ROBERT ROBINSON O.M. D.Sc. Vice-Presidents R. P. BELL M.A. F.R.S. F. BERGEL D.Sc. F.R.T.C. F.R.S. E. R. H. JONES D.Sc. F.R.T.C.,F.R.S. F. G. MANN Sc.D. F.R.I.C. F.R.S. J. M. ROBERTSON M.A. D.Sc. F.R.S. M. STACEY Ph.D. D.Sc. F.R.S. Honorary Treasurer M. W. PERRIN C.B.E. M.A. F.R.I.C. Honorary Secretaries J. CHATT M.A. Sc.D. F.R.I.C. K. W. A. W. SYKES M.A. JOHNSON D.Phi1. Sc.D. Ph.D. A.R.C.S.Ordinary Members of Council C. B. AMPHLETT Ph.D. D.Sc. .4. El. LAMBERTON Ph.D. R. G. R. BACON PIi.D. A.R.C.S. J . W. ialNNErr M.A. D.Phil. F.R.S. L. W. L o m Pli.D. A.R.C.S. D.T.C. G. E. COATES M.A. D.Sc. F.R.T.C. E. A. MOELWYN-HUGHES D.Phil. R. C. COOKSON M.A. Ph.D. A. C. FARTHING M.A. BSc. A.R.I.C. H . T. OPENSHAW M.A. D.Phil. 1. J. FAULKNER Ph.D. F.R.I.C. R. A. RAPHAEL Ph.D. D.Sc.,F.R.I.C. R. H.HALL,P~.D. A.R.C.S.,F.R.I.C. .I. C. RGBB D.Sc. Ph.D. C. €3. HASSALL M.Sc. Ph.D. F.R.T.C. R. H . THOMSON D.Sc.,Ph.D.,F.R.I.C. R. N. HASZELDINE M.A. Sc.D. A. I . VOGEL D.Sc. D.T.C.,F.R.I.C. W. A. WATERS Sc.D. F.R.T.C. F.R.S. B. A. HEMS D.Sc. F.R.I.C. W. B. WHALLFY D.Sc.,Ph.D.,F.R.I.C. E.Y Offieio J. W. COOK D.Sc. F.R.I.C. F.R.S. (Chairman of the Chemical Council) E. D. HUGHES D.Sc. F.R.T.C.F.R.S. (Chaiiman of the Joint Library Committee) D.I.C. D.Sc. Sc.D. F. R.I.C. General Secretary J. R. RUCK KEENE M.B.E. T.D. M.A. Librarian R. G. GRIFFIN F.L.A. QUARTERLY REVIEWS VOL. xrv 1960 Publication Committee Chairmai? H. J. EMEL~US C.B.E. M.A. D.Sc. F.R.S. G. 0. ASPINALL D.Sc. F.R.S.E. WILSON BAKER M.A. D.Sc. F.R.S. R. P. BELL M.A. F.R.S. E. ROYLAND D.Sc. Ph.D. D. M. BROWN Ph.D. G. M. BUKNETT Ph.D. D.Sc. 1. G. M. CAMPBELL B.Sc. Ph.D. N. CAMPBELL D.Sc. Ph.D. N.B. CHAPMAN M.A. Ph.D.,F.R.T.C. J. CHATT M.A. Sc.D. F.R.T.C. D. D. E L ~ Y Sc.D. Ph.D. D. H. EVERETT M.B.E. M.A. D.Phi1. R. 14. HALL Ph.D. A.R.C.S.,F.R.T.C. T. G. HALSALL Ph.D. M.A.,A.R.I.C. D. H. HEY D.Sc. F.R.I.C. F.R.S. D. J . G. IVES D.Sc. A.R.C.S.,F.R.I.C. A. W. JOHW)Y Sc.D. Ph.D. C. KEMBALL M.A. Ph.D. F.R.I.C.F.R.I.C. A.R.C.S. J. A. KITCHEYFK D.Sc. Ph.D. G. KOHNSTAM Ph.D. H. C. LOYC;ULT-HIGC;INS M.A. D.Phil. F.R.S. R. LYTHGOIC M . A . Ph.D. F.R.T.C. F.R.S. H. T. OPENSHAW M.A. D.Phil. M. W. PFRRIN C.B.F. M.A. F.R.I.C. R. A. RAPHAEL Ph.D. D.Sc. P. L. ROBINSON D.Sc. F.R.I.C. K. SCHOFIELD Ph.D. D.Sc. F.R.I.C. A. G. SHAHPC M.A. Ph.D. F.R.I.C. J. C. SPEAKMAN M.Sc. Ph.D. D.Sc. K. W. SYKES M.A. D.Phi1. SIR ALEXANDER T ~ D D M.A. D.Sc. H. C. L. W F I - I ~ Y D.Sc. A.R.C.S. I). H. \VHIFFL.Y M.A.. 5.Phil. M. C. WHITING M.A. Ph.D.,A.R.C.S. G. Wrl KINSOY Ph.D. A.R.C.S. A.R.C.S. F.R.I.C. F.R.S. F.R.I.C. Editor R. S. CAHN M.A. D.Phil.Nat. F.R.T.C. Deputy Editor L. C. CROSS Ph.D. A.R.C.S. F.R.I.C. Assistant Editor A. D. MITCHELL D.Sc. F.R.I.C. L O N D O N T H E C H E M I C A L S O C T E T Y CONTENTS PAGE LAMELLAR COMPOUNDS OF GRAPHITE.By R. C. Croft . . . 1 SHOCK WAVES. By H. 0. Pritchard . . . 46 -LOUR CENTRES IN ALKALI HALIDE CRYSTALS. By M. C. R Symons and W. T. Doyle . . . . . . . . 62 ALKALOIDS OF CALABASH-CURARE AND STRYCHNOS SPECIES. By A. R. APPLICATION OF ELECTRON DIFFRACTION TO THE STUDY OF THE CHEMICAL ARRHENIUS FACTORS (FREQUENCY FACTORS) IN UNIMOLEC ULAR REAC- PRIMARY PROCESSES IN PHOTO-OXIDATION. By R. M. Hochstrasser and Battersby and H. F. Hodson . . . . . . 77 BOND IN CRYSTALS. By B. K. Vainshtein . . . . 105 TIONS. By B. G. Gowenlock . 133 G. B. Porter . . . . 146 PHYSICOCHEMICAL ASPECTS OF SOME RECENT WORK ON PHOTOSYNTHESIS. By R. Livingston . 174 THE BORAZOLES. By J. C. Sheldon and B. C. Smith . . 200 Eastham . . . 221 BENZILIC ACID AND RELATED REARRANGEMENTS.By S. Selman and J. F. TRANSPORT PROPERTIES OF LIQUIDS IN RELATION TO THEIR STRUCTURE. By E. McLaughlin . . 236 CHEMISORPTION OF GASES ON METALS. Tompkins . . . . 257 TETRONIC ACIDS. By L. J. Haynes and J. R. Plinimer . 292 Cross . . 317 By P. M. Gundry and F. C. THE CHEMISTRY OF NATURALLY-OCCURRING 1,2-EPOXIDES. By A. D. THE INTERACTION OF FREE RADICALS WITH SATURATED ALIPHATIC COM- THE PINACOL REARRANGEMENT. By C. J. Collins . * 357 INFRARED SPECTRA OF ADSORBED GASES. By V. A. Crawford . 378 THERMODYNAMICS OF ION ASSOCIATION IN AQUEOUS SOLUTION. By G. H. Nancollas . . 402 POUNDS. By J. M. Tedder . . . 336 ELECTRON RESONANCE IN CRYSTALLINE TRANSITION-METAL COMPOUNDS. By A. Carrington and H. C. Longuet-Higgins . 427 ERRATA . . 454 CUMULATIVE INDEXES . . 455

ISSN:0009-2681    

DOI:10.1039/QR96014FP001

出版商:RSC    

年代:1960

数据来源: RSC

摘要:

SHOCK WAVES By H. 0. PRITCHARD SHOCK waves arise in air because a compressive disturbance can become more and more sudden as time goes on owing to the faster propagation of the high-pressure parts of the disturbance. Weak shock waves are produced by the clap of a hand or the crack of a whip; strong shock waves are equally familiar to us and are associated with for example thunder the motion of supersonic aircraft and projectiles and with explosions of all kinds. The way in which a shock wave builds up can be shown by consider- ing the motion of a wave in which the pressure variation is initially sinusoidal. We consider the disturbance entering a gas at the left-hand side of Fig. 1 and travelling towards the right. Any small pressure disturbance is propagated through the medium with the local velocity of sound and it is a property of any fluid that the velocity of sound increases with pressure.Thus the more intense parts of the disturbance will travel more quickly weaker parts so that the wave-form of the pressure variation as (CHEMISTRY DEPARTMENT UNIVERSITY OF MANCHESTER MANCHESTER 1 3) throughany point in the gas will be a distorted sine wave. This t b c 3 3 m w 4 than the it passes f i m r distonce FIG. 1 distortion increases until after a sufficient distance the high- and low- pressure disturbances arrive simultaneously i.e. the pressure rise becomes instantaneous; this is a shock wave. In fact all sound waves will degener- ate into small periodic shock waves after travelling a few hundred wave- lengths unless sufficiently attenuated by dissipative effects (i.e.diffusion and thermal conduction from the wave). Whilst this effect is of little practical concern a knowledge of the properties of shock waves is of crucial importance in other fields of technology most of them military; like several other techniques in physical chemistry the use of shock waves has filtered through as a by-product of military necessity. The shock tube The behaviour of shock waves is most conveniently studied by using a shock tube. The design of such tubes varies but one suitable for kinetic studies might consist of a metal tube about 6 in. in diameter and say 20 feet long. It is divided into a high-pressure and a low-pressure com- partment by a thin diaphragm (Fig. 2); this diaphragm may be of metal foil celluloid cellophane or some similar material depending on the 46 PRITCHARD SHOCK WAVES 47 High pressure Low pressure (dri v or) tion of the higher-pressure disturbance it becomes sharper until in the sixth profile we have a shock wave.This shock continues to travel along the tube in a uniform manner provided the internal walls of the tube are not too rough. At any instant during the experiment there are four distinct regions in which the local conditions differ very markedly. If we consider the final profile there are the two regions in which the gases are stationary and in the same condition as they were before the experiment started i.e. the as yet unexpanded driver gas at the extreme left and the as yet uncompressed See Payman and Shepherd Proc. Roy. SOC. 1946 A 186,293 for historical references. * White J. Fluid Mechanics 1958 4 585.48 QUARTERLY REVIEWS gas at the extreme right. These two regions may be characterised thermo- dynamically by their pressure density and temperature so that we have Pi(‘) pi(‘) Ti(‘) and Pi pi Ti respectively where the initial temperatures of the driver Ti(‘) and the driven gas Ti are usually the same. We then have a region to the left of the composition boundary which consists of expanded driver gas characterised by Pf(d) p P Tf(d). Finally there is the region which consists of gas which has been compressed characterised by P f pf Tf with Pf = Pf(d); this is the region in which we are interested. This gas has been suddenly compressed and its temperature has risen. The mag- nitude of the temperature rise can be calculated from the Rankine- Hugoniot relations,lPs which are a consequence of the fact that mass momentum and energy must be conserved across the shock front; i.e.if we consider a frame of reference which moves along with the shock front then the mass momentum and energy of the unshocked gas entering from the right must be the same as for the shocked gas leaving to the left. In essence where ,$ is the “pressure ratio” Pf/Pi and+ is a linear function of the average specific heat of the gas between the two temperatures Ti and Tf; in the case of a monatomic gas is independent of time and the pressure ratio 5 can be eliminated if the velocity V of the shock wave is known since v2=- PI t4 + 1 pi 4 - 1 For a weak shock (6 E l) V is only a little greater than the velocity of sound in the unshocked gas but for strong shocks ( f $ l) Vcan be several times the speed of sound and is usually described by a Mach number (i.e.a number of multiples of the velocity of sound in the unshocked gas). Thus if we know the specific-heat function #and the initial state Pi pi Ti of the unshocked gas we can calculate the final temperature if we measure the velocity Y of the shock wave; this is one use for the observation stations at the right-hand end of the tube in Fig. 2. The energy which causes the rise in temperature is derived from the energy of flow of the driver gas down the tube and anything which in- creases the speed of flow of the driver into the low-pressure section will result in a higher value of P&d) (and therefore 5) and consequently a bigger temperature rise. To some extent increasing the driver gas pressure is advantageous but it causes difficulties with diaphragm materials etc.The relevant equations are given in a number of places e.g. (a) Bleakney and Taub Rev. Mod. Phys. 1949 21 584; (b) Bleakney Weimer and Fletcher Rev. Sci. Inst. 1949 20 807; (c) Penney and Pike Rep. Progr. Phys. 1950 13 46 (d) Griffith and Bleakney Amer. J. Phys. 1954 22 597; (e) Hirschfelder Cuttiss and Bird “Molecular Theory of Gases and Liquids” Wiley New York 1954. PRITCHARD SHOCK WAVES 49 Increasing the actual velocity of the driver gas molecules is also useful so that hydrogen or helium is the most efficient driver and it is possible to gain a little extra by heating the driver gas to a high temperature before- hand; this can be done either physically (e.g. an electric heater inside the high-pressure chamber) or chemically (the ignition of a mixture of hydrogen and oxygen in the driver section has been used to initiate the flow4) Another device which roughly doubles the temperature rise is to allow the shock wave to be reflected at the right-hand closed end of the tube whereupon it then begins to move leftwards through the already shocked gas and raises its temperature again ; the quantitative interpretations of reflected shock studies are however open to some criti~ism.~ We can now see what considerations determine the size of the two compartments in a chemical shock tube.Owing to the non-ideal bursting of the diaphragm a good shock is not produced until the compression has moved several diameters down the tube. Then if we wish to study chemical reactions taking place in the hot zone behind the shock sufficient gas must be shock-heated so that the necessary observations can be made before the cold front arrives at the observation post.This determines the length of the low-pressure section and in consequence the driver section must be sufficiently long for the left-moving rarefaction wave not to be reflected back down the tube so as to interfere with the observations. The scope of shock-tube measurements If an inert gas say argon is shocked we have a sharp rise in the temperature pressure and density across the shock front and then a uniform region of hot gas. The discontinuity is very sharp and the distance between uniform unshocked gas and uniform shocked gas is only a few mean-free-paths; i.e. the shock front is only of the order of a micron 0 /O 20 Mach number FIG.4 thick. As the shock strength is increased the shock velocity and the temperature increase until at about Mach 10 the temperature is about 8000"~ (Fig. 4). For stronger shocks however the temperature tails off Resler Lin and Kantrowitz J . Appl. Phys. 1952 23 1390. Strehlow and Cohen J. Chem. Phys. 1959 30 257. 50 QUARTERLY REVIEWS because of the thermal ionisation of the argon atoms; at higher tempera- tures still doubly ionised atoms have been observed in thermal equilibrium with their surroundings. Thus the specific heat of the gas (and the function +) increases by successive steps as the successive ionisation processes become important. If the gas is diatomic other things can happen. Starting with a weak shock travelling only a little faster than sound we can observe effects due to the sort of processes which cause anomalous dispersion in sound waves e.g.rotational and vibrational relaxation. The gas is heated suddenly to a new temperature but it takes many collisions before the molecular rotation and vibration come to thermal equilibrium with the translational motion. Thus the gas behind the shock does not become uniform immediately and by measuring the thickness of this non-uniform region the rate of these equilibration processes can be inferred. At stronger shock strengths temperatures are reached where the diatomic molecule begins to dissociate; this is again a slow process and the rate can some- times be studied under suitable conditions. It may also be possible to study the further reactions of these atoms once they have been produced.At higher temperatures still ionisation again occurs and even this is a slow process; however although rates of ionisation (about 1 psec. at 1 cm. pressure) and recombination have been measured4y6 these are not quantities which have yet found their way into chemical thinking. In addition there is radiation of energy from the shocked gas at most temperatures so that spectral information can be obtained. Shock-tube instrumentation Apart from the obvious pressure-measuring and pumping equipment most of the instrumentation is concerned with the detection of the shock wave the measurement of its velocity and following the variations behind it. If the shock front can be detected and its arrival at the observation post converted into an electrical pulse then the measurement of the velocity simply reduces to the need for a suitable device to time the progress between two adjacent stations.Since the velocity of the shock front is of the order of lo5 cm./sec. and the two observation stations may be 10 cm. apart we have to time an interval of about lo-* sec.; thus to obtain the velocity to better than 1 % needs sub-microsecond electronic techniques. One interesting technique for strong shocks and blast waves is to direct 3 cm. radar waves upstream at the approaching shock and measure the Doppler change in frequency of those waves reflected back by the ions in the shock front.' There are a great variety of methods available for the detection of the arrival of the shock front; they depend on observing the sharp change ' (a) Niblett and Blackinan J. Fluid Mechanics 1958 4 194; (b) Manheimer-Timnat and LOW J.Fluid Mechanics 1959 6 449; (c) Lamb and Lin J. Appl. Phys. 1957 28 754; (d) Toennies and Greene J. Chern. Phys. 1957,26,655. Cook Doran and Morris J. Appl. Phys. 1955 26,426. PRITCHARD SHOCK WAVES 51 in temperature pressure density or in strong shocks conductivity associated with the shock. The detection of a change in electrical conduct- ivity can be particularly simple requiring only a couple of electrodes with a potential across them and a suitable amplifier ;8 automobile sparking plugs can even be used. The method works down to temperatures of 700”~ where there should be no thermal ionisation but the reason for this is not known.9 On the other hand the measurement of the temperature change across the shock is not easy but thin films of platinum or gold sputtered on a Pyrex surface have been used as resistance thermometers;1° the particular thermometers described have time lags of less than 1 psec.Nor is the measurement of the pressure change particularly easy but piezoelectric microphones hot-wire anemometers and mechanical pressure switches have been successfully used. Most of the methods of detection (and measurement) make use of the change in density. There are two optical techniques which give essentially direct pictures of the shock front-the shadowgraph and the schlieren method. In the former method all that is necessary is to trigger an intense flash of light as the shock passes the observation post; the light is colli- mated so as to be parallel when passing through the shock tube and then falls directly on a photographic plate.A shadow is cast by those regions in which the optical depth (i.e. density) has a non-zero second derivative in the plane perpendicular to the light beam.ll In the schlieren method the light from the triggered flash is focused on a second slit after passing through the shock tube and then into a camera; if there are regions in the optical path in which the optical depth (density) has a non-zero first derivative,ll light will be deviated from the observation slit and so cause a shadow to be cast on the photographic record. These two techniques give good qualitative representations of the density change in the shock wave but are of little use for quantitative purposes. However with a third optical technique it is possible to measure the actual change in density across the shock this is the Mach-Zehnder interferometer.12 In this case the light from the triggered spark is collimated and then split into two parallel beams by use of half-silvered mirrors; half the light passes through the shock tube and half through a dummy sample of the un- shocked gas.The two beams are then recombined and interference fringes are obtained. When the density in the shock tube changes the fringes will move and the position of the shock front is therefore indicated by a sharp discontinuity in the fringes. If the beam is off-set so as to make an angle of 1” or 2” with the shock front the discontinuity is spread out and it is * Knight and Duff Rev. Sci. Inst. 1955,26 257. lo (a) Blackman J. Fluid Mechanics 1956,1 61 ; (b) Rabinowicz Jessey and Burtsch l1 Liepmann and Puckett “Introduction to the Aerodynamics of a Compressible l2 Winckler Rev.Sci. Znst. 1948,19,307; Curtiss Emrich and Mack Rev. Sci. Inst. Manheimer and Nahmani Rev. Sci. Inst. 1956,27 174. J. Appl. Phys. 1956 27 97. Fluid” Wiley New York 1947. 1954 25 679. 52 QUARTERLY REVLEWS possible to trace the individual fringes through the shock thus giving an absolute measure of the change in density. Excellent examples of photo- graphs taken by all these three techniques are given in refs. 3(a) 3(6) and 3(4 and in many of the other references quoted in this Review. Another important method of measuring density changes was developed in the study of detonation waves.13 This depends on the change in attenua- tion of X-rays by a gas as the density changes and by using a triggered X-ray flash it is possible14 to measure the ratio of the densities on the two sides of the shock to about &l%.All these methods work with transparent gases. Clearly if the shocked gas is coloured e.g. a halogen relatively simple photometric methods will work; these howeverd will be discussed in relation to the particular problem involved. Spectra and shock waves Since very high temperatures can be attained in strong shocks molecular fragments may be formed in states of high excitation and they will then emit radiation as they fall back to the ground state. For example strong shocks in methane and ammonia emit the spectra of C2 and CN presum- ably formed via C and N atoms.15 If fine dusts (e.g. MgO A120,) are present in the tube even quite moderate shocks (2000"~) will excite the diatomic molecular spectra but much stronger shocks are usually required before the atomic lines appear;le such spectra are of interest for comparison with the emission of meteoric dusts.Quite often spectra are produced from trace impurities in the shocked gas for example strong shocks in argon or krypton have been known to give the Swan bands of carbon and the spectra of CN Hg Ca and Na; the mercury lines appear at a later time than the C2 or CN bands indicating that electronic excitation of mercury atoms by collision is a relatively slow process.17 The sodium-atom spectrum is fairly easily excited and the emission has been used to measure the temperature as a check on the shock-tube equations for the temperature rise.l* In very strong shocks e.g. argon at 18,000"~ the atomic lines suffer broadening and a red shift due to the perturbation of neighbouring ions and e1ectr0ns.l~ Strong shocks in the inert gases also give rise to a continuous spectrum which is emitted after an induction period of some tens of microseconds.This induction period is temperature dependent and in the case of xenon the temperature coefficient over the range 6000-1 1 ,OOO"K corresponds Is Kistiakowsky and Kydd J. Chem. Phys. 1956,25 824. l4 Knight and Venable Rev. Sci. Inst. 1958 29 92. l6 Charatis Doherty and Wilkerson J. Chem. Phys. 1957 27 1415. l6 Nicholls and Parkinson J. Chem. Phys. 1957 26 423. 17 Turner and Rose Phys. Rev. 1955,99,633 ; Rose quoted in Clouston and Gaydon 18 (a) Losev Proc. Acad. Sci. (U.S.S.R.) Phys. Chem. Sect. 1959 120 467; (6) 19 Petschek Rose Glick Kane and Kantrowitz J.Appl. Phys. 1955 26 83. Spectrochim. Acta. 1959 14 56. Clouston Gaydon and Glass Proc. Roy. SOC. 1958 A 248,429. PRITCHARD SHOCK WAVES 53 to an activation energy of 8.3 ev which is the excitation potential of one of the excited states of the xenon atom. These observations are interpreted20 to mean that the Xe atom is excited by collision to Xe*(5s25p56s) and that a stable excited state of Xe is formed by the reaction Xe*+Xe-+Xe,*; this then falls back to its ground state Xe which is repulsive and consequently the radiation emitted must be continuous. The same phenomenon occurs in argon but the excited state is more than 11 ev above the ground state. A continuous spectrum is also emitted from shocks in bromine between 1300" and 2300"~ at pressures of 1-2 atm.21 This arises from a two-body recombination of bromine atoms; no radiation is observed which arises from the normal three-body recombination.Two processes i.e. Br(2P,,2) + Br(2P,,2) and Br(2P,,& + Br(2P3,2) appear to be important; they lead to the formation of excited states of the bromine molecule and these emit continuous radiation in falling back to the ground state. A study of the temperature coefficient of the emission at various wavelengths leads to some information on the actual form of the potential-energy curves for these excited states. Emission however is not confined to the visible and the ultraviolet region. Radiation has been observed in the infrared but measurements are much more difficult because of the lack of suitably fast infrared detectors.However with a lead sulphide detector of 30 psec. response time the infrared emission of the 2-2-0 band in CO has been studied at 2 ~ 3 5 p . ~ ~ The emission builds up rather slowly in pure CO (relaxation time of 77 psec. at 0.24 atm. and 1470"~) but it is not possible because of the experimental difficulties to decide whether the excitation takes place directly i.e. v=0+2 or stepwise i.e. v=0+1-+2. As is common to many of these relaxation processes there is a considerable acceleration by traces of water. Spectral measurements on shocked gases can also be made in absorption. For example air in the range 2000-6000"~ shows the Schumann-Runge bands in abs~rption,~~ and at the higher temperature can be shown to contain about 5 % of NO.24 Shocks in hydrocarbon-oxygen mixtures exhibit absorption corresponding to C and CH for the first 30 psec.but after this only the absorption spectrum of OH persists; on the other hand in shocks using oxygenated compounds e.g. acetaldehyde the C2 and CH spectra do not appear until after the OH has di~appeared.,~ Such obser- vations will help in the interpretation of combustion and explosion processes; clearly they are complementary to the study of spectra in flame gases and explosion products. 2o Roth and Gloersen J. Chem. Phys. 1958 29 820. 21 Palmer J. Chem. Phys. 1957 26 648. 28 Wurster Treanor and Glick J. Chem. Phys. 1958 29 250. e4 Wurster and Glick J . Chem. Phys. 1957,27 1218. l5 Campbell and Johnson J. Chem. Phys. 1957,27 316. Windsor Davidson and Taylor J. Chem. Phys. 1957 27 315. 54 QUARTERLY REVIEWS Vibrational and rotational relaxation in shock waves As mentioned earlier it is possible to study relaxation processes by measuring the thickness of the shock front.In light diatomic molecules the conversion of translational energy into rotational energy may be observed ; in more complicated molecules the equilibration between translational and vibrational energy is important in the shock front. If the rotations were not easily excited the density profile across the shock would be represented by curve 1 in Fig. 5. On the other hand if the Dittonee FIG. 5 rotations take up their energy immediately we have a larger specific heat; thus the temperature rise is not so great and so for the same pressure ratio there is a greater increase in density as in curve 3. In diatomic molecules the rotations come to thermal equilibrium in less than 150 collisions and the density profile is represented by curve 2; we have an initial rise in density similar to that in curve 1 followed by a gradual cooling i.e.a further gradual increase in density until the final state represented by curve 3 is reached. The same happens in the case of vibrational equilibration. In both processes the shock front or region of non-uniform density becomes extended and in the case of vibrational relaxation in very weak shocks may even extend over the better part of a centimetre.26 Three methods have been used to measure the thickness of the front. If it is reasonably thick then the standard interference fringe method can be ~ ~ e d ~ ~ ~ * ~ ~ p ~ ~ with the light beam of course being exactly per- pendicular to the motion of the shock.The second method which has been used fairly extensively is to measure the reflection of a light beam projected at grazing angle to the shock front;28 in the steady state no light is reflected into the detector (apart from some scattering) but there is substantial scattering by the shock front and the duration of this reflection pulse together with the known speed of the shock gives the thickness. The third method which has been used at low densities makes use of the attenuation of an electron beam directed across the tube.29 26 Griffith and Kenny J. Fluid Mechanics 1957 3 286. e7(4Griffith Brickl and Blackman Phys. Rev. 1956 102 1209; (b) Smiley Wider and Slawsky J. Chem. Phys. 1952,20,923; 1954,22 2018. z8 Greene Cowan and Hornig J. Chem. Phys. 1951 19 427; Greene and Hornig ibid.1953,21,617; Anderson and Hornig ibid. 1956,24,767. 29 Ballad and Venable Physics of Fluids 1958 1 225. PRITCHARD SHOCK WAVES 55 The results obtained by these methods are in general agreement with those obtained by other measurements i.e. ultrasonic dispersion pro- jectile studies and impact or pitot-tube measurements. Rotational relaxa- tion in hydrogen takes about 150 collisions and less in other molecules e.g. about 20 collisions in nitrogen or oxygen. Vibrational relaxation in simple molecules is very slow e.g. many thousands of collisions in N, 0, CO, N,O etc. but relatively fast in more complex molecules such as CH or CF2C12. Again the well-known catalytic effect of water is found but it is suggested27a that this effect is confined to bending modes of vibration only; it has long been thought that relaxation occurs via the lowest vibrational mode in the molecule and this would seem to fit in with that idea.Chemical reactions in shock waves The problem of studying a chemical reaction in a shock wave is in general one stage more difficult than the experiments so far described. It is not sufficient just to study the density change; it is necessary to follow the fate of one individual species in the shocked gas and except in the special cases of molecules with relatively intense absorption spectra this is very difficult indeed. One of the earliest reactions to be studied by light absorption was the thermal decomposition N,04+2N0 ;30 this reaction had previously been investigated by ultrasonic dispersion measurements. The shocked gas consisted of a mixture of N2 at 1 atm.containing about 1 % of N204. Although pure N204 could in principle be used admixture with a large excess of a permanent gas means that the shock is moving through an almost perfect gas and this is more convenient because the shock-tube equations in their simplest form apply to perfect gases; the properties of shocks in nitrogen are readily calculable and the presence of 1% of N204 causes only minor corrections to the expected temperature rise. When 2 atm. of N was used as the driver a shock of Mach 1.12 was obtained giving a temperature rise of about 25". The light absorption was measured with a photomultiplier using mercury radiation at about 4000 A. In order to get a reasonable signal to noise ratio it was necessary to use a beam of 1 mm.width and this sets a lower limit on the time resolution attainable at Mach 1 the shock passes a 1 mm. beam in about 3 psec. so that any processes taking place in less than 3 psec. are not observable. As the N,04 is heated its vibrations are excited very quickly and then it begins to dissociate to NO which is coloured and causes a response on the photomultiplier. Above 30°c this rate of dissociation is too fast to measure and the whole shock tube was cooled to -35"c before the beginning of each experiment then over the range of about 20" either side of O"c it was possible to follow the appearance of NO2 over a time measured in a few tens of microseconds. The rate of dissociation was given by k[N,O,] [NJ 9o Carrington and Davidson J. Phys. Chem. 1953,57,418. 56 QUARTERLY REVIEWS with an activation energy of 11.0&0-6 kcal./mole the dissociation energy of N,O is 13 kcal./mole but as we shall see it is common in kinetic dissociation measurements for the activation energy to be rather less than the heat of the reaction.The rate of this dissociation has since been con- firmed by expansion of N,O at a supersonic The dissociation of halogen molecules has been studied by very similar techniques. Iodine,32 for example in high dilution with inert gases dissociates at a convenient rate in the temperature range 1000-1600"~ the rate of dissociation being measured by the decrease in light absorption. The change in light absorption at an observation station as shown on an oscilloscope is represented diagrammatically in Fig. 6. The current before ZQfO ~bsorption t i m e - FIG.6 the shock is determined by the initial I concentration; as the shock arrives the absorption rises sharply owing to the compression of the gas and thereafter begins to fall relatively slowly as the iodine molecules dissociate the rate of dissociation being determined from the initial slope 8. The problem however is not quite as simple as this. The absorption coefficient of any molecule is temperature dependent and it is therefore necessary to measure the variation of absorption with temperature; this can be done by conventional methods at relatively low temperatures but the necessary high-temperature coefficients are obtained from the shock tube traces on the (reasonably valid) assumption that the iodine comes to vibrational equilibrium with its surroundings before it begins to dissociate.In addition allowance has to be made for the fact that as the gas dissociates it cools giving rise to an increase in density and so an increase in absorption; at high I concentrations this can more than offset the decrease due to the reduction in the number of absorbing molecules.33 A correction has also to be made for the contraction which occurs in the time scale at some instant after the shock has passed we are observing a body of gas which was heated not when the shock passed the slit system but at some earlier s1 Wegener Marte and Thiele J. Aeronautical Sciences 1958 25 205; Wegener J . Chem. Phys. 1958,28 724. 32 Britton Davidson and Schott Discuss. Faraday Soc. 1954 17 5 8 ; Britton Davidson Gehman and Schott J. Chem. Phys. 1956,25,804 39 Palmer and Hornig J.Chem. Phys. 1957,26,98, PRITCHARD SHOCK WAVES 57 time because the gas is moving very rapidly along the tube behind the shock; thus gas which was heated about 600 psec. previously will show up on the oscilloscope trace only about 200 psec. after the shock has passed. The initial rate of dissociation is given by where kA is the rate constant for dissociation by collision with argon and k~~ is that for dissociation by collision with another iodine molecule; extrapolation to zero [I,] gives k~ and k1,. As is to be expected from our previous knowledge of collision efficiencies (flash photolysis and other kinetic energy-transfer studies) collisions with iodine are more effective in bringing about dissociation than are collisions with argon. Other gases can be used as diluents and their relative efficiencies measured.The activation energy for the dissociation of iodine comes out to be rather (about 4 kcal.) less than the dissociation energy. Similar measurements have been made on b r ~ m i n e ~ ~ ’ ~ ~ and again the activation energy (31 kcal.) for dissociation is substantially less than the dissociation energy (45 kcal.) ; oxygen also shows this type of behaviour the rate of dissociation being 150 times the maximum rate it could have if the activation energy were equal to the endothermicity.lsa This phenomenon of dissociation with less activation energy than the heat of the reaction appears to be quite common and one suggestion is that the energy of activation need not be solely concentrated in the molecular vibration for the dissociation to take place,33 i.e.some molecules can dissociate by rotation. If we don’t specify any particular energy division the probability that we will find an iodine molecule after a collision with an argon atom having the dissociation energy D concentrated in a specified number n of “effective oscillators” is n-1 e-D/RT A ( 2)‘ 1 RT r=0 \ ’ (2 rotations 1 effective oscillator). The Arrhenius temperature depend- ence of an expression like this is substantially lower than D if n is at all appreciable; in the simple collision we have considered n is very limited but if we consider collisions between pairs of diatomic molecules and allow all their degrees of freedom to contribute to the dissociation of one of them then there is more latitude. Even so it is necessary to strain somewhat the number of important vibrations and rotations in order to get numerical agreement with experiment.An alternative approach to the problem is to consider the mechanism of the reverse reaction i.e. the recombination of the atoms. These have been studied by flash photolysis at lower temperatures and have been shown to have negative temperature coefficients. If we take the shock-wave 84 Britton and Davidson J. Chem. Phys. 1956 25 810. 58 QUARTERLY REVIEWS data and assume a reversible system then the ratio of the forward and reverse rate constants is the equilibrium constant of the reaction and the heat of the reaction is the difference between the two activation energies; since E for dissociation is less than D then E for combination must be negative. However the value obtained from shock measurements at high temperatures is much more negative than that obtained at low tempera- tures from flash photolysis (see Fig.7). The observed activation energy is moo 500 33.3 250 JtK) R G . 7 the difference in average energy between those molecules which react and all those which are present in the system; therefore the meaning of a negative activation energy is that those molecules which react have a lower average energy than the average energy of all the molecules in the system. In a reaction I + I + M -+ I + M the third body M has to carry some energy away to bring the relative I + I energy below the dissociation limit; thus the more energetic the collision between I + I the more energy M must take away. But M is much more likely to take away only a small amount of energy than a large amount.If we make the very simple assumption that M can only take away very small amounts of energy then the average energy of the reacting I atoms is approximately zero; on the other hand the average energy of all the I atoms is RT i.e. 4 kcal. at 2000°K and 1 kcal. at 500"~-hence E at 2000°K is about -4 kcal. and at 500°K about -1 kcal. The Arrhenius curve for such a system has the shape of the broken line in Fig. 7 which is in qualitative agreement with the experimental results but the predicted activation energies are rather especially in the bromine case. We see that neither theoretical approach to this problem is really satisfactory and there is considerable scope for further investigation both in its theoretical and its experimental aspects. Several other dissociation reactions have been investigated directly by light absorption e.g.the dissociation of N205 to NO + of NO2 35 Husain and Pritchard J. Chem. Phys. 1959 30 1 101. 38 Schott and Davidson J. Amer. Chem. Soc. 1958,80 1841. PRITCHARD SHOCK WAVES 59 to NO and 0,37 and of 0 into 0 and O;38 in all these three studies data were also accumulated on some of the subsequent reactions of the dissocia- tion products (e.g. NO2 + NO -+ NO + NO + 0,; NO + NO -+ 2N0 + 0,; NO + 0 +NO + 0,; 0 + 0 -+ 2Ob. In many cases it may not be convenient to study a dissociation reaction by light absorption but nevertheless there are ways in which some relevant information can be obtained. For example it is possible to measure the heat of dissociation as opposed to the activation energy. If the shock is strong enough to dissociate all the molecules then the dissociation energy becomes part of the specific heat function 4 and thereby affects the shock velocity.Thus by measuring the effect of the dissociating gas on the velocity of shocks in say argon one can calculate the contribution the dissociation makes to the high-temperature specific heat and so get the dissociation energy. This has been done for F, N, and CO where the accepted values have been in doubt until recently and values of - 31,39 - 225,6d and - 2566d940 kcal. respectively were obtained. Alternatively one may quench the shock and analyse the products by standard chemical methods. This can be done simply by allowing the shock to expand into a large vessel at the end of the shock tube or better after a sufficient reaction time opening the tube up to a very large evacuated tank by bursting a second diaphragm thereby quenching the reaction by an expansion wave.This method has been used in the study of the pyrolysis of simple hydrocarbons; it has been found that methane cracks with an activation energy of about 101 k ~ a l . ~ 1 (ie. CH -+ CH + H D M 102 kcal.) and also that some curious molecular reactions take place fairly easily,42 e.g. 2C,H2 -+ C,H + H (E E 30 kcal.) and 2CH4 -+ C2H6 + H,. Also in reflected shocks the method has been used in the study of the reaction N + 0 + 2N0 at high temperatures., It appears that the reac- tion is a chain reaction ; oxygen having much the lower dissociation energy decomposes into atoms and the rate-determining step is 0 + N -+ NO + N; this reaction has an activation energy of about 74 -+ 5 kcal.compared with the endothermicity of about 76 kcal. at 2500"~. This technique of shocking a mixture of gases one of which has a much lower dissociation energy than the other lends itself to the study of atomic reactions and has been used to study the reaction Br + H2 by using bromine-hydrogen mixtures., Similarly in using hydrogen-oxygen mixtures,45 the hydrogen dissociation predominates and it is possible to follow the rate of formation of OH radicals by the reaction H + 0 -+ OH . 37 Huffman and Davidson personal communication. 38 Jones and Davidson personal communication. 39 Wray and Hornig J. Chem. Phys. 1956,24 1271. 40 Knight and Pink J. Chern. Phys. 1958 29 449. 41 Skinner and Ruehrwein J. Phys. Chem. 1959,63 1736. 42 Greene Taylor and Patterson J.Phys. Chem. 1958 62 238. 43 Glick Klein and Squire J. Chem. Phys. 1957 27 850. 44 Britton and Davidson J. Chem. Phys. 1955 23 2461. 45 Schott and 'ECinsey J. Chem. Phys. 1958,29 1177. 60 QUARTERLY REVIEWS + 0. There is an induction period before the radicals are detected but this is not an induction period in the true sense the concentration of radicals is followed by their ultraviolet absorption and it takes time for this concentra- tion to build up to 1 x mole/l. which is the minimum detectable; from the subsequent build-up the activation energy for H atom attack on oxygen molecules was found to be 17 kcal. The close relation of this experiment to detonation studies need hardly be emphasised. Although it is possible as we have seen to study a number of chemical reactions some of which cannot be investigated by other methods or alternatively can only be observed in some other temperature range yet these experiments are fairly tedious and subject to considerable in- accuracies.For one thing it is not easy to estimate concentrations very precisely from cathode-ray tube traces and the mainly electronic problem of time resolution is aggravated somewhat by the time contraction which occurs. Mention has already been made of the variation of spectral absorp- tion coefficients with temperature and the cooling effect the reaction may have if it is dissociative. In addition suppose that it is possible to measure the shock velocity to 1 % which is about as good as can be expected the temperature rise depends roughly on the square of the velocity i.e.we have an uncertainty of about 2% which on a temperature rise of 1500” is &30”. This makes the temperature scale for activation energy plots a little less precise and in some such experiment as say the reaction of H with 02 the calculated H atom concentration is subject to significant un- certainty. Finally mention should be made of the simple physical difficulty of making a large metal shock tube vacuum-tight and the length of time it takes to pump it out to say mm. before each experiment can begin. These limitations however have not prevented the accumulation of a substantial body of important information. Other applications of shock waves So far in this Review our attention has been confined to shock waves in gases. Shocks can also be propagated through liquids and solids and have been used to measure compressibilities and derive equations of state.One of the more interesting chemical aspects of shocks in solids is the possibility of so compressing a non-metallic solid that it becomes metallic -for example at shock pressures of 250,000 atm. phosphorus shows an electrical conductivity characteristic of a metal ;46 a similar observation has been made with sulphur.47 A further application of shock waves in solids is in the production of what are known as “tactical” nuclear weapons. An amount of fissionable material which is less than the critical mass is surrounded with a shell of trinitrotoluene. When the conventional explosive is detonated a shock wave moves towards the centre of the 48 Alder and Christian Discuss. Faraday SOC. 1956 22,441.47 David and Hamann J. Chem. Phys. 1958 28 1006. PRITCHARD SHOCK WAVES 61 system and compresses the fissionable material above its critical density so causing a sub-critical amount of material to explode.48 Mention has already been made of the crucial importance of a knowledge of the behaviour of shocks caused by supersonic aircraft and rocket nose- cones and of the importance of knowing how hot (and how corroded) the structure will become as a result of its interaction with the hot nitrogen and oxygen ions or atoms which are produced.49 Other war-time studies were concerned with the effect of blast waves on buildings and upon animal and human life-for example to find out what sort of shock pressures cause the collapse of an ear-drum or hzmorrhage of the In astrophysics the coalescence of masses of interstellar gas appears to lead to shock waves and it is possible that solar flares are some sort of shock phenomenon; an attempt has been made to explain the difference in electronic and kinetic temperatures of the sun in such terms.50 Finally mention should be made of the field of magnetohydrodynarnics and the production of very strong shocks.Supposing we have a glass tube with a single-turn copper coil around it,6a and discharge a suitable con- denser through the coil. A rapidly varying magnetic field is produced (dH/dt E 70,000 gauss/psec.) and this induces an electric field which is intense enough to ionise the gas inside the tube. The resulting current of ions is then accelerated by the intense magnetic field to very high velocities up to about Mach 90 in the experiment quoted.The production of these very high Mach numbers leads to the possibility of thermonuclear fusion reactions taking place in a shock tube. Attempts are being made to reach temperatures of several million degrees in this kind of way by producing an ionised gas (plasma) and subjecting it to an intense magnetic shock. One of the technical problems involved is to get a sufficiently fast build-up of the magnetic field say to 1500 gauss in 0.2 psec. ; this requires electrical circuits of sufficiently low impedance for the current to build up at the rate of lo6 amp./psec. or more. These and other related problems are discussed in the first few papers of the Conference on Extremely High Temperatures held in Boston in March 1 958.51 48 Pauling “No More War!” Dodd Mead New York 1958. 49 Hertzberg Jet Propulsion 1956 26 549. 6o Sen Phys. Rev. 1953 92 861. 51 Fischer and Mansur (editors) Conference on Extreme:y High Temperatures Wiley New York 1958.

ISSN:0009-2681    

DOI:10.1039/QR9601400046

出版商:RSC    

年代:1960

数据来源: RSC

摘要:

COLOUR CENTRE§ IN ALKALI W I D E CRYSTALS By M. C. R. SYMONS and W. T. DOYLE* (THE UNIVERSITY SOUTHAMPTON) 1. Introduction A REMARKABLE wealth of information of interest and significance extending well beyond the field of solid-state physics has recently been forthcoming from studies of the spectrophotometric and magnetic properties of colour centres in ionic crystals. It is our aim here to describe and discuss the simplest of these systems namely additively coloured alkali halide crystals and to give some indica- tion of the situation in other systems. Our treatment will be brief and selective. The reviews by Seitz1.2 are outstanding and exhaustive other major works dealing with specific aspects will be referred to when appro- priate. In general colour centres are found whenever a new species is in- corporated into the alkali halide crystal to give what may be described crudely as a solid solution.However the geometry of the crystal imposes severe limitations on the size shape and charge of the solutes. We can distinguish two classes of “solutes” (a) Those which are derived from the cations or anions of the host crystal (sections 2 and 3) and (b) those which are unrelated to the host crystal (section 4). Alkali halide crystals have two great advantages as host crystals they are transparent from the far infrared to the far ultraviolet region (about 2000 A) where the fundamental absorption of the crystal begins. In addition the simplicity of the lattice geometry and the nearly complete ionic character of the bonding greatly simplify the interpretation. When considering colour centres of class (a) it is convenient to describe those which are derived by addition of metal as electron-excess centres and those derived from halogen as electron-deficit centres.Experimentally these can be formed separately by treatilig the crystal with metal or halogen vapour or together by exposure to high-energy radiation. Since such exposure can be carried out at low temperature several spectral features occur which are lost on warming and are not formed by the addition procedures. Additions give rise to relatively simple spectra and will be considered in the greater detail. The situation can be pictured in a simple way by considering what chemical reactions are to be expected for alkali-metal and halogen atoms in a fluid medium and then how they are likely to be modified by the crystal lattice.* National Science Foundation Postdoctoral Fellow on leave of absence from the Department of Physics Dartmouth College Hanover New Hampshire U.S.A. Seitz Rev. Mod. Phys. 1946 18 384. Seitz Rev. Mod. Phys. 1954 26 7. 62 SYMONS AND DOYLE COLOUR CENTRES IN ALKALl HALlDE CRYSTALS 63 Alkali-metal atoms have one overriding tendency namely to donate electrons to any available acceptor. In the absence of an acceptor they may dimerise but this bonding is very weak and at room temperature condensation to metal will normally occur. In contrast halogen atoms besides being powerful electron-acceptors can dimerise to give relatively stable molecules. In the presence of halide ions an equilibrium involving trihalide ions would be established (1 1 Hal + Hal- + Hal,- .. . . If the concentration of halide ions is large compared with that of halide atoms dihalide radical-ions can be formed (2) Hal. -t Hal- + Hal,- . . . . The bonding must be weak but there is evidence that these radical-ions are important intermediates in the flash photolysis of halide ions in water.3 Within the lattice in the absence of impurities the simplest electron- acceptors are anion vacancies which have an effective positive charge centred on the vacancy. It can be shown theoretically that alkali-metal atoms cannot exist as such in an undistorted lattice site and therefore they must be trapped interstitially combine to form metallic units or ionise in such a way that the electrons are trapped in anion vacancies and the result- ing cations occupy cation vacancies.An electron in an anion vacancy termed an F-centre is the simplest electron-excess centre [Fig. 1 (b)]. FIG. 1. Models for electron-excess centres. (4 (6) (c) (4 c4 V) w and represent anion and cation vacancies. represents an electron in an anion vacancy. (f) and ( g ) are alternative models for the M-centre. Other varieties of electron-excess centres formed by combination of elec- trons and vacancies are discussed in section 2. Similarly a halogen atom in an alkali halide crystal cannot exist at a regular lattice point. An interstitial atom would probably combine with a neighbouring ion to form a dihalide anion or migrate to a more stable site. If spatial requirements are satisfied formation of molecular halogen and trihalide negative ions would be expected. However it is commonly supposed that the most fundamental and simplest of electron-deficit centres would be the antimorph of an F-centre that is a system of similar configuration but with a reversal of sign.Such a unit termed a V centre by Seitz1*2 and symbolised in Fig. 2 (a) consists of a cation vacancy and a “hole” symmetrically distributed around the vacancy. That is to say that Grossweiner and Matheson J. Phys. Chem. 1957 61 1089. 64 QUARTERLY REVIEWS at any given instant one could picture one halogen atom and five halide ions around the cation vacancy but that on average all the six surround- ing halide ions share the “hole” created by the absence of an electron and hence the unit has spherical symmetry. FIG. 2. Models for electron-deficit centres (after Seitz2). (4 6) (el (4 o represents the absence of an electron from one of the halide ions surround- ing the vacancy.Since the spectra of several of these electron-deficit units such as the trihalide ions are known they can be compared with the bands observed in additively coloured crystals. These bands found in the near-ultraviolet region and generally described as V-bands are discussed in section 3. 2. Electron-excess centres Alkali halide crystals prepared with a stoicheiometric excess of alkali- metal either by heating them in the presence of the metal vapour4 or by electrolysis just below the melting point5 may exhibit a variety of optical absorption bands. In general these electron-excess bands occur in the lower- energy half of the region of transparency of the host crystal. The particular type of coloration observed depends in detail upon the optical and thermal treatment to which the crystal is subjected after introduction of the metal.Although a large variety of such colour centres exists they may be con- veniently grouped according to their mode of formation in additively coloured crystals. The F-Centre.-When a crystal is heated in the presence of alkali-metal vapour and then quenched rapidly a single narrow absorption band the F-band is found. The excess of alkali-metal ions is incorporated in the crystal and causes the formation of cation vacancies in which according to de Boer’s model of the F-centre the excess of electrons is trapped.2 This vacancy model which has been generally accepted for some time has now been established beyond reasonable doubt by the results obtained from magnetic resonance studies.In view of these results which are discussed briefly below there seems little point in considering alternative models for the F-centre such as those discussed by Seitz.2 Detailed wave functions all based on the vacancy model have been presented and recent experi- mental studies have been designed to give results which probe the suitability of these treatments. We will mention some of the most significant proper- ties of I;-centres and then give a brief resume of the basic features of the Rogener Ann. Phys. 1937 29 386. Heiland 2. Physik. 1950 127 530. SYMONS AND DOYLE COLOUR CENTRES IN ALKALI HALIDE CRYSTALS 65 mathematical treatments. For details the reader is referred to a com- prehensive and critical treatise by Gourary and Adrian,g and to a review by Dexter' in which the optical properties are discussed in detail.One of the most interesting features of the F-bands in alkali halides is that the wave- lengths of the band maxima are a simple function of the nearest-neighbour distance a. Ivey* has given an empirical equation for the wavelength A,,,. (A) = 703~zl*~~ which reproduces the experimental data within 7 %. It is noteworthy that the electron-affinity of the cations does not seem to be an important pal ameter and any theoretical treatment should reproduce this dependence upon the nearest-neighbour distance. Another important yardstick against which wave functions for the F-centre must be judged is the wealth of detailed information obtained from the application of electron-spin r e s o n a n ~ e ~ J ~ ~ ~ ~ J ~ and electron- nuclear double resonance techniques.13 When crystals containing F-centres are placed in an intense magnetic field the two-fold degeneracy of the electron spin is removed and transitions between these levels can be induced by suitable irradiation with microwave energy.The resulting absorption curve is generally broadened or split into components (described as hyperfine structure) by interactions with the magnetic moments of the surrounding nuclei. It is this hyperfine structure which provides the most useful information since one can deduce from the number of lines and their relative intensities the number of equivalent nuclei interacting and it is generally a simple matter to identify the nuclei involved. At the same time the separation of individual lines derived from a given nucleus is a function of the time the unpaired electron spends near that nucleus and hence a very detailed picture of the electron distribution can be built up.The results show that the unpaired-electron density is quite high on the six cations which define the vacancy. Somewhat surprisingly it is also appreciable on the first shell of anions although it is only just detectable on the second shell of cations. Early wave-functions for the F-centre were calculated on the assumption that the crystal could be treated as a polarisable continuum the ionic nature of the lattice and the characteristic periodic potential being largely ignored. This approximation can be correct only if both the ground and the first excited state are diffusely spread over many ions in the vicinity of the vacancy.In fact the simple models based on this approximation prove to be inconsistent since the resulting wave functions are far too compact for the continuum model to be a valid approximation and hence this simplification must be rejected.6 Indeed the results of electron-spin Gomary and Adrian Solid State Physics in the press. ' Dexter Solid State Physics 1958 6 353. * Ivey Phys. Rev. 1947 72 341. * Hutchinson ibid. 1949 75 1769. lo Schneider and England Physica 1951 17 221. l1 Kahn Kittel Levy and Portis Phys. Rev. 1953 91 1066. l2 Lord Phys. Rev. Letters 1958 I 170. l3 Feher Phys. Rev. 1957 105 1122. 3 66 QUARTERLY REVIEWS resonance show conclusively that the electron is closely confined to the vacancy and the first cation and anion shells; this volume is far too small to justify a continuum model.The other extreme would be to use an infinitely deep square-well model with a radius equal or close to the interionic distance. However a better approximation is to use a well of finite depth with a constant potential inside it and a coulombic potential outside it. This semi-continuum theory has been greatly refined by various workers and is discussed in detail by Courary and Adrian.6 These more refined calculations give good agreement with experiment when applied to the calculation of the energies and intensities of the F-bands and reasonable values for the hyperfine inter- actions can also be obtained provided one includes the reasonable exten- sion that when close to an ion the electron behaves like an s-electron in the outermost shell of that ion.The linear combination of atomic orbitals (LCAO) molecular-orbital approximation has also been used to describe the cavity model of F-centres and was particularly important in the development of the underlying theory of electron-spin resonance in F-centres.l1 However by far the most satisfactory and versatile approximation for the F-centre is the “point-ion- lattice” approximation of Gourary and Ad~-ian.~~l~ These authors have compared their treatment with the continuum and the molecular-orbital approximation in their review,6 and have extended it to cover other electron-excess centres. Agreement with experiment is good both for the energies of the F-bands and for the hyperfine splitting constants and other data derived from electron-spin resonance spectroscopy. The model uses the Hartree-Fock approximation in which the dipoles induced by the F- electron on the surrounding ions point to the centre of the vacancy rather than following the detailed motion of the electron.In view of the success of these calculations the following conclusions can be drawn with some confidence (a) the F-electrons are to be found largely within the vacancy and hence (b) polarisation of the surrounding ions is small since the trapped electron will largely cancel the effect of the missing anion; (c) displacement of the ions surrounding an F-centre from the normal lattice position is small; (4 the electronic transition which gives rise to the F-band may be described as p t s to a first approximation and even in the excited p-state the electron is closely confined to the vacancy.Although the vacancy model satisfactorily accommodated most of the properties of the F-centre until recently there was one notable exception. It can readily be shown that F-centres should luminesce on excitation with high quantum efficiency at low temperature.15JG However all evidence pointed to the contrary until in 1954 Botden van Doorn and Haven1’ l4 Gourary and Adrian Phys. Rev. 1957 105 11 80. l5 Huang and Rhys Proc. Roy. Soc. 1950,204 A 406. l6 Pekar J . Exp. Tlzeor. Phys. (U.S.S.R.) 1952 22 641. l7 Botden van Doorn and Haven Philips Res. Reports 1954 9 469. SYMONS AND DOYLE COLOUR CENTRES IN ALKALI HALIDE CRYSTALS 67 published results which showed that the predicted luminescence was readily detected if crystals were used which contained only I;-centres and that the quantum efficiency was indeed high under these circumstances.18 When there is appreciable aggregation the excitation energy is apparently dispersed by other processes involving these aggregate centres and it was for this reason that luminescence from F-centres proved so hard to detect.This aspect is discussed in more detail in the section on aggregate centres. F‘- a- and /I-Bands.-The F-band is always accompanied by a narrow band /I in the ultraviolet region close to the long-wavelength edge of the first fundamental band of the cry~ta1.l~ The band is therefore assigned to a transition involving the anions surrounding the F-centre. If the F-band is bleached by radiation of somewhat higher energy than the F-band maximum the /I-band is also bleached and a new band a is found on the long-wavelength side of the P-band.Simultaneously a broad band labelled F’ grows on the low-energy side of the narrow F-band. Since there is a decrease in paramagnetism as the F-band is bleached and since quantum-efficiency measurements show that in favourable circum- stances two F-centres are destroyed for every quantum absorbed,,* the effect of irradiation seems to involve the ejection of one F-electron from its anion vacancy trap and its capture by another F-centre. The I;’-centre is thus two electrons with paired spins trapped at a single anion vacancy. The a-band is then due to the excitation of electrons on those anions which surround an anion vacancy whilst the P-band is a similar transition when the vacancies contain F-electrons. These transitions may be similar in nature to that for anions in normal lattice sites or they may be caused by electron-transfer from an anion into the vacancy to give momentarily an F-centre (a-band) or an F‘-centre (/I-band).Aggregate Centres R M N.-When light is absorbed within theF-band at room temperature numerous new absorption bands may be formed on the long-wavelength side of the F-band;21 Seitz has suggested that the new bands are due to electrons trapped at aggregates of vacancies.1t2 The criterion of simplicity together with a consideration of possible formation mechanisms led Seitz to suggest specific models for these centres (Fig. 1). The R model is an electron trapped at a pair of adjacent anion vacancies the R2 model is two electrons trapped at a similar vacancy pair. Thus the models correspond to F2+- and F2-centres.That is if one compares the F-centre with a hydrogen atom then the R and the R model are analogues of the hydrogen molecule ion and the hydrogen molecule respectively. Seitz’s model for an M-centre is an electron trapped at a cluster of two anion vacancies and one cation vacancy. All of these centres have lower than cubic symmetry [Fig. 1 (d e andf)]. It should be emphasised that van Doorn Philbs Res. Reports 1958 13 296. l9 Delbecq Pringsheim and Yuster J. Chern. Phys. 1951 19 574; 1952,20 746. 2o Pick Ann. Physik. 1938 31 365. 21 Petroff 2. Physik. 1950 127 443. 68 QUARTERLY REVIEWS there is still no convincing evidence that they are correct. However most of the available evidence is consistent with these models. Much of the data relating to aggregate centres is still based upon plausible formation mechanisms.An example of such arguments may be mentioned. The aggregate centres are not produced simultaneously.21 The M-band appears first followed by R,. The rate of production of R,- centres is proportional to the concentration of M-centres. Cole and Friauf22 explain this genetic relation using Seitz’s models as due to capture of an electron by an M-centre followed by the ejection of a positive ion vacancy. This sort of reasoning can hardly be taken as establishing the models. More direct evidence on aggregate centres is obtained from symmetry studies. Ueta23 has shown that polarised light absorbed in the M-band leads to dichroism thus establishing that the M-centre has lower than cubic symmetry in qualitative agreement with Seitz’s model. Corroboration of this symmetry is obtained from measurements of the polarisation of luminescence excited by polarised 25 The problem is complicated by evidence presented below that centres which are close together but not adjacent can interact strongly.26 Some at least of the asymmetry detected by polarisation studies could be caused by such interaction between centres which in isolation might have cubic symmetry.Another experimental result which gives information about the symmetry of M-centres is the observation by Overhauser and RUchardt2’ that no linear Stark effect could be detected in the M-band. One can conclude from this negative result that M-centres should have inversion symmetry a conclusion which conflicts with Seitz’s model. Knox28 has suggested a modified model which whilst being in accord with all other information relating to M-centres also possesses inversion symmetry.This model can also be used to explain the otherwise puzzling absence of a dielectric loss peak.29 Knox assumes that this configuration shown in Fig. 1 (g) may actually be stabilised by lattice relaxation. Such a configuration may be thought of as a neutral alkali atom strongly dis- torted by the surrounding lattice. Since the composition of the M-centre in both Knox’s and Seitz’s models is the same no reappraisal of formation and bleaching experiments is necessary. It should be possible to distinguish easily between the two configurations by using the new electron- spin double resonance methods13 because of the difference in symmetry. Moreover one would expect a considerable hyperfine splitting due to the central nucleus for Knox’s model.Conventional electron-spin resonance 22 Cole and Friauf Phys. Rev. 1957 105 1464. 23 Ueta J. Phys. SOC. Japan 1952 7 107. 24 van Doom Philips Res. Reports 1957 12 309. 25 Lambe and Compton Php. Rev. 1957 106 684. Compton and Klick Phys. Rev. 1958 112 1620. 27 Overhauser and Ruchardt Phys. Rev. 1958 112 722. 28 Knox Phys. Rev. Letters 1959 2 87. 29 Jacobs J. Chem. Phys. 1957 27 218. SYMONS AND DOYLE COLOUR CENTRES IN ALKALI HALIDE CRYSTALS 69 has already been observed in M-~entres,~~ but the large inhomogeneous broadening of the lines has prevented any detailed conclusions regarding the nature of the centre. Seitz’s models assign R,- and R,-bands to two different centres consist- ing of one or two electrons trapped at two neighbouring anion vacancies.It has been observed however that the ratio of the intensity of the R,-band to that of the R2-band is constant over a range of concentrations. This has led Herman Wallis and Wallis31 to suggest that the two bands represent different transitions of the same centre. Again it should be possible to distinguish between these alternatives by using electron-spin resonance since the R1 model would give rise to paramagnetism whereas the R model would not. Crystals containing aggregate centres exhibit a number of interesting phenomena which may be termed interaction eflects. Of these we shall list only a few as being typical and particularly interesting. (a) The quantum efficiency of the conversion of F- into F‘-centres on irradiation decreases with repeated bleaching and thermal reconstitution of the F-band.32 (b) In a crystal containing both F- and M-centres irradiation with polarised “3’-band” light gives rise to dichroism of opposite sign in the M - b a n d ~ .~ ~ From the conditions of this experiment it appears that reorientation of M-centres is involved. (c) Irradiation in the F-band produces luminescence characteristic of R- and M-bands in crystals containing aggregate centres.28 (d) Irradiation at WOK in any of the bands produces a temporary change in the bands some being increased in intensity and others d e c r e a ~ e d . ~ ~ > ~ ~ All these effects may be explained by the existence of an efficient inter- action mechanism. Thus (a) would simply require the energy absorbed by the F-centre to be transmitted to an A-centre say which could undergo a radiationless transition to its ground state.Alternatively the energy could be utilised by an R-centre for dissociation. Similarly in case (b) the energy absorbed by the F-centre could be utilised by a neighbouring M-centre to reorient itself. The mechanism for preferential reorientation is obscure but may simply be that interaction with light is a minimum for one particular orientation which is thus favoured on irradiation. Case (c) involves energy exchange between centres followed by re-emission as light a phenomenon well known in the general field of luminescence. The high efficiency of the process however suggests a greater proximity than would be deduced from the concentration of the various centres. This may indicate a segregation of all of the centres in specific regions of the crystals pos- sibly along dislocation lines.Such a segregation is known to occur in the later stages of c~agulation.~~ Case (4 provides striking evidence for interaction for it was found that 30 Lord Phys. Rev. 1957 106 1100. 31 Herman Wallis and Wallis Phys. Rev. 1956 103 87. 32 Geiger Phys. Rev. 1955 99 1075. 33 van Doorn and Haven Phys. Rev. 1955 100 753. 34 Amelinckx Phil. Mag. 1956 47 269. 70 QUARTERLY REVIEWS irradiation in the infrared region (M-band) in sodium chloride produced changes in the absorption spectrum in the ultraviolet region. Since it is hardly likely that bands so widely spaced in wavelength could overlap appreciably this observation is interpreted as implying a particularly close proximity of centres. As Compton and Klick have pointed out,26 such strong interaction between centres may invalidate earlier conclusions regarding the symmetry of aggregate centres drawn from polarisation measurements.Interaction effects certainly complicate the analysis of the properties of aggregate centres. However they also offer a new intriguing field of study. The Colloid Band-The F-band obtained by rapidly quenching hot additively coloured crystals does not represent an equilibrium state. When the concentration of F-centres exceeds the solubility of the metal there is a tendency for the excess of metal to coagulate in the form of colloidal particles. The F-band is then replaced by a new band at longer wavelengths. This band which we shall describe as the “colloid band” is thought to be a property of the colloidal metal.All the known features of this band- position width shape integrated intensity and the fact that its properties are independent of temperature-are determined by the optical constants of the metal and the index of refraction of the host lattice. It can be shown that this result is in accord with the concept that the colloid band is caused by transitions of electrons in the colloidal metal the position of the band can be computed by using Mie’s theory35 for the absorption of light by metal ~ p h e r e s ~ ~ ~ ~ ’ and by using the free-electron theory for alkali-metals it can be shown3* that there is an intimate connection between the colloid band and the theory of collective modes of os~illation.~~ Thus the optical properties of colloid centres seem to be well understood. A considerable body of independent evidence is available to show that colloidal particles of reduced metal are present in crystals when the colloid band appears e.g.electron-diffraction rnea~urements,~~ X-ray ~cattering,~~ and nuclear magnetic resonance.42 This evidence will not be described here but a glance at the references enumerated would convince the reader that the identification of this band as a property of colloidal metal rests on firm ground. The mechanism of colloid formation is not yet well understood. In particular the action of light and the r61e of impurities deserve further study. It is known that concentrated arc light can cause coagulation of 35 Mie Ann. Phys. 1908 25 377. s6 Savostianova 2. Phys. 1930 64 262. 37 Scott Smith and Thompson J. Phys. Chem. 1953,57,757. 38 Doyle Phys.Rev. 1958 111 1067. 39 Pines Rev. Mod. Phys. 1956 28 184. 40 McLennan Cunad. J. Phys. 1951,29 122. 41 Smallman and Willis Phil. Mag. 1957 48 1018. 42 Ring O’Keefe and Bray Phys. Rev. Letters 1958 1 453. SYMONS AND DOYLE COLOUR CENTRES IN ALKALI HALIDE CRYSTALS 71 electron-excess but only if the specimen is allowed to become warm under the intense ill~mination.~~ If in high concentration F-centres will coagulate in the dark.45 A heterogeneous equilibrium analogous to a vapour-solution reaction exists between F-centres and colloid particles if light is excluded. The heat of the dark reaction was and found to be in agreement with the cohesive-energy data for bulk Although light is unnecessary for coagulation in densely coloured crystals Theisen and Scott4' found that the rate of coagulation was enormously enhanced by illumination.S h a t a l ~ v ~ ~ ? ~ ~ has examined the effect of light alone using small concentrations of F-centres so that thermal coagulation did not occur. Light within the F-band produced coagulation at 250°c even in the absence of thermal coagulation. The 3'-band was replaced by a band labelled X which was displaced by about 0.5 ev to the low-energy side of the 3'-band. This is probably the same band which Scott and B ~ p p ~ ~ called R'. Shatalov attributes it to the F2 molecular centre but its position and temperature- dependence seem to suggest that it is due to very small colloidal particles of reduced metal. The kinetics of formation and destruction of X-centres will bear closer examination since they are very early products in the coagulation process.They offer an interesting meeting ground between aggregate centres (R M etc.) which are produced optically at room temperature and the larger colloidal particles which are formed in heavily coloured crystals by thermal coagulation. The r61e of impurities in stimulating and suppressing colloid formation can throw light on the initial steps in coagulation. It is known thatsmall quantities of bivalent cations can greatly inhibit colloid formation,50 possibly by altering the equilibrium vacancy concentration^.^^ Conversely hydroxyl ions may well be necessary for the formation of colloids in irradiated crystals,52 but are not needed to promote coagulation in addi- tively coloured crystals. However hygroscopic salts such as sodium bromide are particularly hard to colour additively suggesting that hydroxyl ions may assist coagulation even in additively coloured crystals.Hydroxyl ions are present in synthetic crystals unless special pains are taken to exclude water vapour. There is every indication that this im- purity affects other properties besides the coagulation of colloids (cf. section 4).53954 43 Glaser Nachr. Akad. Wiss. Gottingen 1936 3 31 44 Scott and Bupp Phys. Rev. 1950 79 341. 45 Scott and Smith Phys. Rev. 1951 83 982. 46 Scott Phil. Mag. 1954 45 610. 47 Theisen and Scott J. Chem. Phys. 1952 20 529. 48 Shatalov Soviet Physics J.E.T.P. 1956 2 725. 49 Shatalov Optika i Spektrosk. 1957 3 610. Heiland and Kelting 2. Phys. 1949 126 689. 51 Watson and Scott J. Chem. Phys. 1958 30 342. aa Compton Phys. Rev. 1957 107 1271. 53 Rolfe Phys.Rev. Letters 1958 1 56. 54 Etzel and Patterson Phys. Rev. 1958 112 11 12. 72 QUARTERLY REVIEWS 3. Electron-deficit centres In 1954 Seitz2 made a strong plea for a systematic study of electron- deficit ( V ) centres which at that time were not well understood. Since then some light has been thrown upon the problem but much still awaits clarification. Seitzl9 offered an interpretation of the various V-bands in terms of centres which are direct antimorphs of the electron-excess centres dis- cussed in section (2). His V,-model consists of a hole combined with a cation vacancy symbolised as in Fig. 2 (a). By “hole” is meant the absence of a single electron from the outer shells of those halide ions directly surrounding this vacancy the unit is therefore centrosymmetric.Seitz’s Yz- V3- and V,-centres are also shown in Fig. 2. This approach failed to take note of the strong tendency of halogen atoms to form covalent bonds and it now seems clear that in general the V-bands are not so much properties of the imperfect solid as of isolated molecules or ions trapped within the solid. Certain bands in the ultraviolet region are always designated as Vl V, V, etc. for specific crystals but there is no certainty that the same centre is being described in different crystals. We therefore deal with each halide in turn. Iodides.-Since no magnetic studies of V-centres in alkali iodides have yet been reported only spectrophotometric results can be discussed. Additive coloration with iodine invariably gives rise to two intense bands at about 3650 and 2950 1$.55-57 These bands are found with about the same relative heights under different conditions and the separation between them is approximately equal to the energy difference between the 2P3/2 and the 2P112 state of the iodine atom.It therefore seems likely that these bands are caused by a single centre. Hershs7 has pointed out that tri-iodide ions in various solvents have two intense ultraviolet absorption bands with maxima close to the 3650 and 2950 A bands of additively coloured crystals and has suggested therefore that these bands are due to I,- ions incorporated in the crystals. This is in accord with chemical expectation. It is not clear however how the lattice changes to accom- modate these ions. It is curious that the low-energy band is more intense than that of higher energy in the crystal doublet whereas the reverse is true for I,- in solution.It is possible that other bands are present in the crystal spectrum which are not resolved under the conditions used or that distortion in the crystal considerably alters the relative intensities of the two transitions. Uchida and Nakai56 found a third band at about 2600 1$ in potassium iodide crystals. No chemical analogue is known for this band and further study is required before an assignment can be made. 55 Mollwo Ann. Phys. 1937 29 394. 54 Uchida and Nakai J. Phys. SOC. Japan 1954 9 928. 57 Hersh Phys. Rev. 1957 105 1410; J. Chern. Phys. 1957,27 1330. SYMONS AND DOYLE COLOUR CENTRES IN ALKALI HALIDE CRYSTALS 73 Molecular iodine has a fairly strong absorption band in the 5000 A region. Since the formation of tri-iodide ion is energetically favoured free iodine is not likely to be a stable species in the crystal but Hersh has reported two bands in this region in potassium iodide under unspecified condition^.^^ Bromides.-Potassium bromide coloured with bromine has been studied more extensively.An intense band in the 2700 A region generally pre- dominates. This is very close to the peak found for Br3- ions in various solvents and is probably due to these ions. M o l l ~ o ~ ~ found a weak band at about 4200 A this is close to the position expected for molecular bromine and the band shape is also similar to that found for bromine in solution. It therefore seems likely that both Br and Br3- are formed. Another band at 2300 A was found by Mollwo and also by Her~h:~' it is unlikely that this band is due to Br3- since Teegarden58 found an intense band at 2740 A but no band at 2300 A.Also the spectrum of Br3- ions in solution is a single broad line rather than a doublet. Teegarden however did find a shoulder at about 3200 A which was also found by D ~ r e n d o r f ~ ~ in crystals exposed to X-rays at -140". Since no simple molecular or ionic species is known with bands either at 3200 or at 2300A no clear identification can be made. A combined magnetic and optical study might prove helpful in this connection. Teega~den~~ found that potassium iodide crystals treated with bromine gave spectra which were indistinguishable from those treated with iodine under similar conditions. This can be understood in terms of the concepts outlined in this section since bromine readily oxidises iodide to iodine (3) Br + 21- + I + 2Br- However a similar result was found for potassium bromide treated with either bromine or iodine and the reverse reaction (3) is not energetically favourable.It is more probable that under these conditions Br,- and BrI respectively are formed. Since these ions have bands at 2700 and 2600A respectively it would be difficult to distinguish between fhem. It is possible however that the large excess of bromide ions is sufficient to upset equilibrium (3) and that iodide ions are formed from iodine. Teegarden rejected this possibility on the grounds that no band for I- was detected in the 2150 A region. However when iodide is incorporated in a potassium bromide lattice60 the first excited band is strongly shifted towards the higher-energy region being at 1930 A at 77°K.This is outside the range studied by Teegarden. Chlorides.-Unfortunately it has not been possible to form V-centres in alkali chlorides or fluorides by additive coloration. Therefore we have to 58 Teegarden J. Chem. Phys. 1956 24 161. 69 Dorendorf 2. Phys. 1951 129 317. 6o Delbecq Robinson and Yuster Phys. Rev. 1954 96 262. . . . . 4 74 QUARTERLY REVIEWS turn to the results obtained with high-energy radiation. At room tempera- ture two bands are found both for sodium chloride and for potassium chloride in the 2300 A region (Va and the 21 50 A region ( V3). By analogy with solution spectra it is probable that the V2-band is due to C&- but the assignment is not clear cut since the V2- and the V,-band lie close together. One might expect to find spectrophotometric evidence for the presence of “free” chlorine whose 117u+1C transition lies at about 3330 A.This is normally a weak transition and might well be too small for measurement but a weak band at 3400 A found by Hersh5’ for potassium chloride pellets could be due to free chlorine. When alkali chlorides or bromides are exposed to high-energy radiation at low temperatures and the spectra measured at the same temperature two new bands in the near ultraviolet region appear which are irreversibly lost on warming. Seitz2 has speculated on the nature of the centres respons- ible for these bands (which are symbolised as V and H) but there is still insufficient information concerning them to enable definite conclusions to be drawn. However electron-spin resonance studies have conclusively proved the presence of C1,- ions in potassium chloride crystals X-irradiated at low temperature.61 It was thought at first that the Y,-band was due to this radical ions1 and it has also been suggested that the resonance was caused by V,-~entres~~ [Fig.2 (c)]. In fact neither postulate is correct and none of Seitz’s models is suitable. The ions have an absorption band at 3650 A in potassium chloride which had not been detected previously because of its proximity to the V,-band (- 3500A).63 The electron-resonance results are of great importance since the wealth of detail is such that identification is unambiguous. These ions represent the simplest possible electron-deficit centre in which a chlorine atom formed by loss of an electron has combined with any one of its neighbour- ing chloride ions no lattice vacancies appear to be involved and the absorption band is close to that attributed to C1,- ions in aqueous s01ution.~ Thus the Vl-bands still remain enigmatic.There is no evidence against Seitz’s model but the inability to detect any electron-spin resonance which can be linked to this band is hard to understand in terms of this model. The band for potassium chloride is close to that for molecular chlorine but the intensity is too great and studies with polarised light suggest that the centre has cubic Cohen Kanzig and Woodruffs5 recently identified the radical ion F2- in irradiated lithium fluoride. They suggested that this unit was closely similar to Seitz’s Y,-model and it would be of great interest to make a combined magnetic and optical study similar to that of Delbecq et aL6 61 Kanzig Phys.Rev. 1955 99 1890. Bagguley and Owen Reports Progr. Phys. 1957 20 304. 63 Delbecq Smaller and Yuster Phys. Rev. 1958 111 1235. 64 Lambe and West Phys. Rev. 1957 108 634. 65 Cohen Kanzig and Woodruff Phys. Rev. 1958,107 1096. SYMONS AND DOYLE COLOUR CENTRES IN ALKALI HALIDE CRYSTALS 75 The particular items discussed in this section establish conclusively that the formation of specific molecules plays a fundamental r81e in the field of electron-deficit centres. Many outstanding problems remain and it is felt that these should be viewed in terms of interactions between vacancies and the molecular species whose formation now seem established. The results of Miessner'j6 and are of great significance in this respect their studies of mixed alkali halide crystals whilst still lacking a complete interpretation clearly show the difference between &centres and V- centres.4. Foreign ions A remarkably large number of cations and anions can be incorporated in alkali halides to give crystals which are ideal for spectrophotometric and magnetic studies. Of these we choose to discuss briefly hydride ions hydroxide ions alkaline-earth metal ions and first-row transition-metal ions of low valency. Hydride Ions.-Because it consists of only a proton and two electrons the hydride ion can adapt itself to fit any alkali halide lattice giving what is often described as a U-centre. Because of this flexibility the U-band which may be described as the first fundamental band of the hydride ion depends strongly upon the lattice constant just as does the F-band.Other bands associated with hydrogen are found after high-energy irradiation of crystals containing hydride. A combined magnetic and spectrophotometric study6* has greatly helped to elucidate the reactions involved and has established that hydride ions are photolysed with ultra- violet light to give F-centres and interstitial hydrogen atoms. A band (V,) found on the long-wavelength side of the U-band after irradiation is thought to be due to these interstitial hydrogen atoms.68 Hydroxide Ions.-These ions can replace halide ions in certain crystals and are of great importance because this may well happen unintentionally and hence phenomena caused by hydroxide ions may be ascribed to the pure c r y ~ t a l . ~ ~ ~ ~ On photolysis with ultraviolet light in the fundamental hydroxide band hydrogen atoms ( Uz) and F-centres are detected for potassium chloride but for potassium bromide a prominent V,-band is also found.Since the primary step probably gives H- and 0.- this difference can be understood in terms of the reaction (4) 0.- + Br- -+ 02- + Br* (V,) . . . Whilst this is favoured in a bromide lattice the greater electron affinity of chlorine could well prevent its occurrence with potassium chloride. Alkaline-earth Cations.-Any cation with an electron-affinity greater O6 Miessner 2. Phys. 1953 134 567. 67 Pick Z. Phys. 1953 134 604. 88 Delbecq Smaller and Yuster Phys. Rev. 1956 104 599. 76 QUARTERLY REVIEWS than that of the host cation is a potential electron-trap. This is certainly true for alkaline-earth cations and the resulting centres which are to a first approximation the corresponding singly charged cations (e.g.Ca+) give rise to characteristic optical spectra69 and electron-spin resonance ab~orption.~~ These centres are generally designated Z, irrespective of the particular cation involved. Transition-metal Cations.-Lithium fluoride has been used as host crystal for magnetic studies of ions such as Cr+ Mn2+ Fe+ Co2+ Co+ and Ni+ by Bleaney and ha ye^,^^^'^ the monopositive ions being formed by exposing crystals containing the corresponding bivalent ion to high-energy radiation. In many cases a measure of the covalent character of the bonds between impurity ions and the six neighbouring fluoride ions can be deduced because such interaction gives rise to a hyperfine structure in the electron-spin resonance spectra.Univalent ions (Cr+ Fe+ and Co+) are found to have cubic symmetry but bivalent ions (Co2+ and Mn2+) are in surroundings of less than cubic symmetry. This suggests that there is a cation vacancy close to the bivalent ions which migrates away during the irradiation. Extensive studies of this sort have also been made by Wertz and his co-workers using magnesium oxide as host crystal.73 5. Conclusions The most outstanding development in this field has been the application of electron-spin resonance methods including double resonance. When this is combined with optical studies a great deal of information can be obtained which besides establishing the basic characteristics of the centre being studied provides data which the theoretician can use as a yardstick for detailed mathematical descriptions.It is perhaps not always realised how many unusual compounds are studied in this field we have already mentioned many such as FZ2- C12- Ca+ and Fe+ and doubtless many more will soon be discovered. These highly reactive species have not only been detected but have often been subjected to more detailed structural analysis than is afforded to stable compounds. Those interested in solution chemistry can also draw from the results of these studies. This has been done for example in the field of solutions of alkali metals in ammonia and other solvents,74 and comparison with crystals may also be relevant when considering ionic s ~ l v a t i o n . ~ ~ G 9 Pick Ann. Phys. 1939 35 73. 70 Kawamura and Ishiwatari J. Phys. SOC. Japan. 1958 13 574. 71 Bleaney and Hayes Proc. Phys. SOC. 1957 70 B 626. 72 Hayes Discuss. Faraday SOC. 1958 26 58. i s Wertz Auzins Griffiths and Orton Discuss. Faraday SOC. 1958 26 66. 7 4 Symons Quart. Rev. 1959 13 99. Smith and Symons Trans. Faraday SOC. 1958 54 338 346.

ISSN:0009-2681    

DOI:10.1039/QR9601400062

出版商:RSC    

年代:1960

数据来源: RSC

摘要:

ALKALOIDS OF CALABASH-CURARE AND STRYCHNOS SPECIES By A. R. BATTERSBY M.Sc. PH.D. and H. F. HODSON PH.D. (DEPARTMENT OF ORGANIC CHEMISTRY THE UNIVERSITY BRISTOL) NEWS of the dramatic paralysing effect of the South American Indian arrow and dart poisons known as curare was carried back by the early explorers of that continent and has held the interest of men of science and medicine since the sixteenth century. This interest was increased by the mystery surrounding the preparation of the poison and many fantastic stories became connected with it. These are included in an entertaining account of the history preparation and pharmacology of curare given in McIntyre’s excellent rnon0graph.l Recently a collection of authoritative accounts of all aspects of curare has been published2 as the proceedings of a UNESCO Symposium held in 1957; the present Review is desirable be- cause of the spectacular advances made in knowledge of the chemistry of curare since that time.As pointed out by McIntyre curare is a generic term which includes many types of arrow-head poison prepared in South America and the constitution of individual preparations varies according to geographical origin. All curares are powerful poisons which paralyse voluntary muscle2 and all are concentrated aqueous extracts of plant material. Boehm3 classified curares according to the type of container used to pack the final product; he writes of tube-curare packed in bamboo tubes pot- curare for which earthen pots were used and calabash-curare held in calabashes or gourds. Although the validity of this classification has been q~estioned,~ in particular the existence of pot-curare as a distinct group it is useful for this discussion to accept the broad division into tube-curare and calabash-curare.It was early realised3 that the active principles of curare are water- soluble quaternary alkaloids and in 1935 King5 isolated the now well- known curarising agent d-tubocurarine (1) from tube-curare ; d-tubocurar- McIntyre “Curare Its Natural History and Clinical Use” University of Chicago Press Chicago 1947. Bovet Bovet-Nitti and Marini-Bettolo (editors) “Curare and Curare-like Agents” Elsevier 1959; see also Craig “The Alkaloids” Vol. V ed. Manske Academic Press New York 1955 p. 265. Boehm Abhandl. KgZ. sachs. Ges. Wissensch. 1895 22 201; 1897 24 1. Lewin “Die Pfeilgifte” Barth Leipzig 1923; Gill Anesthesiol.1946 7 14. King J. 1935 1381. 77 78 QUARTERLY REVIEWS ine is an example of a quaternary bisbenzylisoquinoline alkaloid. Tube- curare is prepared mainly from the bark of Menispermaceous plants particularly the genus Chondrodendron and d-tubocurarine was later isolated by Wintersteiner and Dutcher from C. tomentosum6 Further work by King7 and others led to the isolation and structural elucidation of many more bisbenzylisoquinoline alkaloids from these sources. Calabash-curare originates in the northern parts of the South American continent particularly in the Amazon and Orinoco basins. It is con- siderably more active physiologically than tube- or pot-curare and has presented much more formidable chemical problems. Some of the major problems however have now been overcome and efforts have been increased owing not only to the rich and fascinating chemistry involved but also to the pharmacological interest of the curare alkaloids.d-Tubo- curarine chloride and synthetic curare agents with essentially the same action are now extensively used in surgery in conjunction with light anzesthesia. With their aid it is possible to achieve the required degree of muscular relaxation necessary for successful surgery without recourse to potentially dangerous deep anzsthesia. The interest attaching to the much more active calabash-curare alkaloids is thus obvious. Over a century ago Robert Schomburgke was able to see barks of Strychnos toxifera and other Strychnos species being used as important constituents of calabash-curare. This has been confirmed by later observa- tions and is also apparent from the general similarity in alkaloid content between calabash-curare and extracts from the bark of various Strychnos species.It has been shown particularly well by the extensive chromato- graphic studies of Marhi-Bettolo and his collaborator^.^ Thus chemical investigations of calabash-curare and of the barks of Strychnos species are mutually related topics and can bz conveniently considered together in this Review. An exhaustive survey of work in this field which has been largely carried out over the last decade has been published by Bernauer.1° Isolation of Pure Alkaloids.-Serious chemical work on calabash-curare was started by Boehm3 in 1897 and resulted in the isolation of a highly active amorphous principle ; much later (1 935) King" described the preparation of an equally active amorphous quaternary iodide from the bark of S.toxifera. However the first isolation of crystalline calabash- curare alkaloids was achieved by H. Wieland and his scho01.~~-~~ The Wintersteiner and Dutcher Science 1943 97 467. King J. 1948 265 and earlier papers. Penna Iorio Chiavarelli and Marini-Bettolo Gazzetta 1957 87 1 163 and earlier a See ref. 1 page 33. lo Bernauer Forschr. Chem. org. Naturstofe 1959 17 184. l1 King Nature 1935 135 469. le Wieland Konz and Sonderhoff Annalen 1937 527 160. l3 Wieland and Pistor Annalen 1938 536 68. Wieland Pistor and Bahr Annalen 1941 547 140. l6 Wieland Bahr and Witkop Annalen 1941 547 156. papers. BATTERSBY AND HODSON CURARE ALKALOIDS 79 German workers precipitated the quaternary alkaloids as a mixture of reineckate salts which was then fractionated by adsorption chromato- graphy on alumina; of the various reineckate fractions they obtained some yielded crystalline chlorides and picrates.C-Curarine I chloride* was the first calabash-curare alkaloid to be so isolated ; other well-characterised alkaloids isolated in this early work were C-calebassine and C-dihydrotoxi- ferine I from calabash-curare and toxiferine I and toxiferine I1 from the bark of S. toxifera. Using the same chromatographic technique Kinglo also isolated toxiferine I and toxiferine I1 from S. toxifera together with a series of new alkaloids all in small quantity designated toxiferine 111-XII. Recently it has been shown17 that several of these salts 111-XI1 are identical with well-characterised alkaloids described after King’s original paper; toxiferine V and toxiferine XI are identical with toxiferine I.Though chromatography of the alkaloidal reineckates was a major step forward in fractionation technique the method has its drawbacks. For example it has been found1’ that well-separated bands on the column can all contain the same quaternary alkaloid. It is now firmly established that the most satisfactory fractionation procedure in this field is partition chromatography on cellulose developed by the Zurich and Munich ~ c h o o l ~ . ~ ~ ~ ~ ~ Most of the present total of about seventy pure curare alkaloids have been isolated by this technique. Some idea of the com- plexity of the isolation problem can be gained from Schmid Kebrle and Karrer’s demonstration18 that at least forty-one alkaloids were present in a sample of calabash curare from the Amazon basin; even the single plant material Strychnos toxifera examined by Battersby Binks Hodson and Ye0we11,~~ contains at least thirty quaternary alkaloids.Extensive fractiona- tion involving repeated chromatography on cellulose and alumina is usually required before crystalline alkaloids can be obtained. The Table shows those alkaloids isolated from calabash-curare and Strychnos species which have been sufficiently studied to warrant their inclusion in this Review; little can be said at present about the other forty or so alkaloids and it will suffice to give their names and references to their isolation in the Appendix. Even during the early investigations by Wieland and King it became probable that the curare alkaloids are indole derivatives and with recent advances particularly from Karrer and Schmid’s group it is possible to correlate the ultraviolet spectra of many of the alkaloids with one or other of six related chromophores.These are the indoline (2) methyleneindoline * (a) The quaternary alkaloids are often isolated and handled as the chlorides and it is therefore convenient to use the name of the alkaloid as meaning alkaloid chloride. Thus in the sequel C-curarine I means C-curarine I chloride and other alkaloids will be treated in the same way. Anions other than chloride will be named. e.g. toxiferine I picrate (b) The letter C- denotes calabash. l6 King J. 1949 3263. l7 Battersby Binks Hodson and Yeowell J. in the press. lS Wieland and Merz Gem. Ber. 1952 85 731. Schmid Kebrle and Karrer Helv.Chim. Actu 1952,35 1864. 80 - YO. - 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 - QUARTERLY REVIEWS Alkaloids of Calabash-curare and Strychnos species Alkaloid ~~~ Toxiferine I C-Dihydrotoxiferine I C-Alkaloid H Nordihydrotoxiferine Caracurine VI E Caracurine I1 methochloride C-Alkaloid D Caracurine V Caracurine VII Hemitoxiferine I C-Calebassine C-Alkaloid A C-Alkaloid F C-Alkaloid Y C-Cararine I C-Alkaloid E C-Alkaloid G C-Curarine I11 E C- Flu or ocur arine Diaboline C- Mavacurine Melinonine A Melinonine B C-Alkaloid T Lochneram C-Fluorocurine Melinonine G Melinonine F ;ormula of cation or base 0.42 1.2 0.71 1.2 1.6 0.8 0.42 0.34 1.4 2.1 1.5 0.8 0.23 0.49 1.6 1-0 0.36 0.65 2.2 2.7 4.0 2.7 3.1 2.1 3.2 2.0 - Chromophore Meth yleneindoline 9 Y 9 9 Indoline Y Modifiez indoline Endoline "(a) as NH] Y Y Y9 Indoline carbinolamine Y9 Y 9 Y Y 3 Y 3 ) Unknown 9 9 See p.97 N- Acy lindoline Indole 9 9 3 93 Y $-Indoxy1 8- Carbolinium 8-Carbolinium The mobilities of the alkaloids on paper are referred to that of C-curarine I as in solvent "c".18 distance moved by toxiferine 1- distance moved by C-curarine I standard. Thus RC for toxiferine I = c These formula may still need revision particularly in respect of the hydrogen 2o Kebrle Schmid Waser and Karrer Helv. Chim. Acta 1953 36 102. 21 Asmis Waser Schmid and Karrer Helv. Chim. Acta 1955 38 1661. z2 Asmis Schmid and Karrer Helv. Chim. Acta 1954 37 1983. 23 Asmis Bachli Giesbrecht Kebrle Schmid and Karrer Helv. Chim. Acta 1954 content. 37 1968. BATTERSBY AND HODSON CURARE ALKALOIDS 81 - q0.- 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 - Alkaloids of Calabash-curare and Strychnos species-continued Clolour with ceric sulphate immediate-After 20 min. Red-violet-Colourless Blue-violet-Colourless Red-violet-Colourless Violet-Pale brown Purple-Brown Purple-Brown Violet Red-violet-Yellowish Purple-red-Brown Stable orange Stable orange Blue-violet-Carmine Blue-violet-Carmine Blue-violet-Carmine Red-violet-Olive green Blue-Chrome green Blue-Chrome green Blue-Chrome green Blue-green-Yellow-green Nil Carmine Nil Nil Very pale red - Red-violet-Brownish Nil Nil Physiological activityb 9 y 2o 30y 2 o 16y 2o Inactive 22 Inactive 22 Over 400 y l6 llOOy 2o Inactive 22 Inactive 22 1140y 21 240y 2o 7 0 y 2o 75y 2o 30y 2o 0 - 3 - 4 - 0 y 2o 0.6-5.0 y 2o 1800y 2 o *Inactive 24 ?Inactive lQ ?Inactive 25 tInactive 2s - - - - 4400y 2 o - - First isolation S.toxifera15 (Br. Guiana) Calabash15 Calabashla S. toxiferu21 (Venezuela) S. toxiferu22 (Venezuela) S. toxifera22 (Venezuela) S. t~xifera'~,'~ (Br. Guiana) Calabashla S. toxifera22 (Venezuela) S. toxifera22 (Venezuela) S. tq.xiferu17 (Br. Guiana) Calabash15 Calabashla and S. t o ~ i f e r d ~ ~ ' ~ Calabash18 Calabash2s Calabash" Calabashla Calabash1* Calabash14 S. diab01i~~ Calabash' S. melin~niana~~ S. melinoniana26 Calabash2s Calabash27 S. melin~niana~ S. melinoniana2 t~ The figures give the dose in y (pg,) per kg. for the head-drop assay on the mouse;s0 the figures marked * are for head-drop assay on the rabbit,ls and the results marked t are for toxicity test on the frog.1s$25 24 King J.1949 955. 25 Schlittler and Hohl Helv. Chim. Acta 1952 35 29. 26 Arnold von Philipsborn Schmid and Karrer Helv. Chim. Acta 1957 40 705. 27 Arnold Berlage Bernauer Schmid and Karrer Helv. Chirn. Acta 1958 41 1505. 28 Schmid and Karrer Helv. Chim. Acta 1947 30 2081. 2Q Bachli Vamvacas Schmid and Karrer Helv. Chirn. Acta 1957 40 1167. * O Waser Helv. Physiol. Pharmacol. Acta 1950 8 343. 82 QUARTERLY REVIEWS (3) indole (4) oxindole (5) or N-acylindoline (6) $-indoxy1 (7) and fi-carbolinium (8) systems. In some alkaloids simple modifications of these systems are involved for example the carbinolamine (9). The groups in the Table have been constructed on the basis of chromophore and it is worth drawing attention to the close connection between chromophore and colour reaction with ceric sulphate.C-Mavacurine C-FluGocurine and C-Alkaloid Y.-A first insight into the structures of alkaloids from calabash-curare came from a study of C-mavacurine and C-fluorocurine. The former was isolated by Wieland and Merz19 and the latter by Schmid and Karrer;28 both were subsequently found in S. tuxifera from Venezuela.22 Work on these alkaloids was greatly U+ OH + o-o- I 0-H \ \ 0 5) (14) (13) 0-1 _H+ 0-1 Q-1.S. ' Y"- N 6 ." (a) OH f +OH facilitated by the discovery by Karrer Schmid and their co-workers31 that they are structurally related. Thus the quaternary C-fluorocurine C20H2502N2+ which clearly showed the 2,2-disubstituted #-indoxy1 chromophore (1 0) was reduced to hydrofluorocurine (partial structure 1 1) by borohydride.Acid then catalysed the illustrated rearrangement which is of 2,2-disubstituted 3-hydroxyindolines (1 l) to yield a 2,3- disubstituted indole (partial structure 12). The indolic product was identical with natural C-mavacurine. Fritz Wieland and B e s ~ h ~ ~ were able to extend the relationships by making use of the extensive researches 31 Bickel Giesbrecht Kebrle Schmid and Karrer Helv. Chim. Acta 1954 37 553; Bickel Schmid and Karrer ibid. 1955 38 469. 32 Witkop J. Amer. Chem. SOC. 1950 72 614; Witkop and Patrick ibid. 1951 73 713. sa Fritz Wieland and Besch Annalen 1958,611 268. BATTERSBY AND HODSON CURARE ALKALOIDS a3 of Witkop and Patrick34 on simple tetrahydrocarbazoles. Oxidation of C-mavacurine (partial structure 12) catalytically with oxygen over platinum gave a product to which the partial structure (14) was assigned; this is no doubt formed by way of the peroxide (13).The product had the properties of a glycol and-what was important-was rearranged by acid as illus- trated to give C-fluorocurine (partial structure 10). Since the intermediate (14) was found to be identical with C-Alkaloid Y previously isolated from a calabash,23 a triad of related alkaloids was available ; structural informa- tion derived from one alkaloid can thus be used for the other two. C-Fluorocurine contains an ethylidene side chain (>=CHMe) an acetylatable hydroxyl group and one N-methyl group the last being attached to the quaternary N(b) These functions and the analytical evidence require that C-fluorocurine be pentacyclic and the foregoing correlations show that this also holds for C-mavacurine.A clue to the probable arrangement of three of these rings came from selenium de- hydrogenation of normavacurine the tertiary base derived by pyrolysis of the quaternary C-mavacurine. This degradation yielded a b-carboline derivative (1 6) which was not fully identified because of the minute amount t t Me \ I ;C-fj Me-CH-Et - Me-flH-Et * CO,H C ' I \ (20) 0 r) available a common difficulty in the curare field. However the spectral properties of the N(b)-methiodide of the degradation base particularly the stability of the chromophore towards alkali showed clearly that the indolic nitrogen N(a) is alkylated;31 it should be mentioned for comparison that the spectrum of the salt (17) is profoundly changed by alkali owing to the formation of the anhydro-base (1 8).Further catalytic hydrogena- tion of hydrofluorocurine (partial structure 11) resulted in Emde degrada- tion to a tertiary base (20) which unlike the starting material gave a-methylbutyric acid (21) onKuhn-Roth oxidation.31 This result establishes the presence in hydrofluorocurine of a quaternary allylamine system as in (1 9) which would undergo Emde degradation and reduction as illustrated. Witkop and Patrick Experientia 1950 6 183 and subsequent papers. 84 QUARTERLY REVIEWS Because of the cyclic set of changes shown in the partial formulae (10) +( 12)+( 14)+( lo) it is certain that the conversion of C-fluorocurine into C-mavacurine only involves the $-indoxy1 to indole change and so the same system (19) is also present in C-mavacurine. The foregoing evidence can now be combined in partial structure (22) for C-mavacurine and there remain two carbon atoms for construction of two rings free from C-methyl groups.These requirements can be met by the constitution (23) which Bickel Schmid and Karrer propose31 for the alkaloid ; no firm proposal is made for the site of the hydroxyl group though position 15 is favoured. un CHMe HO 07) The plausible biogenetjc arguments by which this structure is derived involve the indicated intramolecular cyclisation of the supposed inter- mediate (24) used in biogenetic theory for such alkaloids as corynantheine (25). Future developments here both structural and stereochemical will be of great interest for though the proposed constitution for C-mavacurine is not yet fully established it is clear that this alkaloid represents a new twist in the biogenetic pattern for the indole alkaloids.If formula (23) is correct for C-mavacurine it is certain that structure (26) represents C-fluorocurine ; C-Alkaloid Y then has structure (27). Alkaloids of Strychnos meZinoniana.-As a result of extensive fractionations by Schlittler and HohlZ5 and more recently by Bachli and his c o - ~ o r k e r s ~ ~ eleven new alkaloids have been isolated from this plant and named melinonine A and B and melinonine E to M inclusive. Structural studies have been described for four of these. BATTERSBY AND HODSON CURARE ALKALOIDS 85 The structure of melinonine F Cl3HI3N2+ was fairly clear29 on the basis of its ultraviolet absorption spectrum (P-carbolinium salt chromo- phore) and the alkaloid was shown by direct comparison to be the N(b)- metho-derivative (28) of harman.Melinonine F has the distinction of being the simplest quaternary alkaloid to be isolated from South American Strychnos species. Melinonine G C1,H,,N,+ is also notable for its low hydrogen content; in keeping with this its ultraviolet and infrared spectra are very similar to those of sempervirine salts (29) and moreover the spectra established U Et the absence of vinyl residues. On the basis of this and other evidence particularly the catalytic reduction of the alkaloid to an indolic product which contained a C-ethyl group Bachli and his c o - ~ o r k e r s ~ ~ propose structure (30) for melinonine G. The constitution (31) then follows for the indolic reduction product. Structure (30) is in fact the one rigidly established by Bejar et aZ.35 and by Hughes and R a p o p ~ r t ~ ~ for flavopereirine from Geissospermum species.There seems little doubt that melinonine G and flavopereirine are identical though no direct comparison has apparently been made. Melinonine G is a particularly interesting molecule because in terms of current biogenetic thinking it must be regarded as a degraded indole alkaloid. Thus it could be formed from the common intermediate (24) proposed for many indole alkaloids by the loss of the three carbon atoms attached to C(15) in a reversed Michael reaction. Aromatisation could then give the required system. The other two alkaloids melinonine A and melinonine B have rather more complex structures. A key degradation product in the chemistry of the former was obtained by Schlittler and H ~ h l .~ They found that melinonine A C,,H2,03N2+ could be pyrolysed to give the corresponding tertiary base normelinonine A C21H2,0,N2 which yielded alstyrine (32) on selenium dehydrogenation. Further chemical and spectroscopic evidence derived from normelinonine A established the presence of an indole system together with the group MeO,C-k=k-O- a common feature in 35 Bejar Goutarel Janot and Le Hir Compt. rend. 1957 244 2066. 56 Hughes and Rapoport J. Arner. Chem. SOC. 1958 80 1604. 86 QUARTERLY REVIEWS the indole alkaloid field. These results led directly to the gross formula (33) as a likely one for normelinonine A and direct comparison with tetra- hydroal~tonine~~ (33) established the identity of the two bases. Thus melinonine A is the A@)-metho-derivative of the base (33).The chemistry of the tetracyclic melinonine-B is not as yet so clear-cut though structure (34) is a likely one. The presence of an acetylatable hydroxyl group a vinyl group an indolic “3 and a quaternary / q X & ’ H2 ‘ Et (3 4) Y2 CH2-OH methylammonium group has been firmly established by Vamvacas et aL3* There is no C-methyl group in the alkaloid so that the hydroxyl group must be placed in the primary position as in formula (34) in order to accommodate the other evidence. Selenium dehydrogenation of dihydro- melinonine B gave an a-pyridylindole having the highly characteristic ultraviolet absorption of this system ; structural work on this degradation product was hampered by the very small amount available but there is reasonable evidence in favour of structure (35).Surprisingly dehydrogena- tion of melinonine B over palladium yielded yobyrine (36) which on the basis of structure (34) must have been formed by ring-closure of the side- chains. This result is rather disturbing in that it increases the difficulty of 87 Elderfield and Gray J. Org. Chem. 1951 16 506; Wenkert and Roychaudhuri J. Amer. Chem. SOC. 1957,79 1519. 38 Vamvacas von Philipsborn Schlittler Schmid and Karrer Helv. Chim. Acfu 1957,40 1793. BATTERSBY AND HODSON CURARE ALKALOIDS 87 degradative work in the indole field; no longer can the isolation of yobyrine be taken as proof of the presence of a carbocyclic ring E in the parent alkaloid (e.g. structure 37). It can be seen that the foregoing evidence is not sufficient to establish firmly structure (34) for melinonine B; it could be objected for example to constitution (34) that the side-chains on positions 15 and 20 might be interchanged as Vamvacas et al.have been careful to point The resulting structure would be less attractive biogenetically but clearly further investigation of melinonine B is desirable. However with the present knowledge of its structure we can add melinonine B to the growing number of a-indole alkaloids* which do not contain a carboxyl group. Until recently the presence of a carboxyl group seemed to be general in the a-indole series. Yohimbine (37) is just one example of the many bases which display this feature. C-Alkaloid T (0-Methyisarpagine) and Lochneram.-The non-phenolic C-Alkaloid T C20H2402N2 isolated in Zurich from a Brazilian calabash,26 is now known to be identical with O-methyl~arpagine~~ which in turn is identical with 10chnerine;~~ thus structural studies on this interesting base are available from several laboratories.There is rigid evidence for an isolated double bond which is present in part as ‘CH-CH=CH2 and in part as ‘C=CHMe since ozonolysis gives a mixture of formaldehyde and acetaldehyde. This means that “C- Alkaloid T” is really a difficultly separable mixture of vinyl and ethylidene isomers. It is also established that a 5-methoxyindole residue unsubstituted at N(a) three more rings and a C-methyl group are present. The primary nature of the hydroxyl group was shown very neatly26 by reducing the 0-tosyl derivative to the corresponding deoxy-derivative. This contained a new C-methyl group probably located as MeCH” or less probably as / / \C /c M e d - C since its Kuhn-Roth oxidation products did not contain \C propionic acid only acetic acid.All this evidence can be accommodated by the constitution (38) for * a-Indole alkaloids are those involving the p-carboline system (a) or some simple derivative of it e.g. (6). A (0) (b) sD Stoll and Hofmann HeIv. Chim. Acta 1953 36 1143; Stauffacher Hofmann and Seebeck ibid. 1957,40,508; Poisson Le Men and Janot Bull. SOC. chim. France 1957 610. O0 Mors Zaltzman Beereboom Pakrashi and Djerassi Chern. andInd. 1956,173. 88 QUARTERLY REVIEWS C-Alkaloid T which is based26 on an assumed relation between this alkaloid and ajmaline; ajmaline has been rigidly proved41 to have structure (39). However there are considerable gaps to be filled before structure (38) is proved to be valid.Lochneram was isolated by Arnold et aL2’ from the calabash which yielded C-Alkaloid T and is the A@)-metho-derivative of the latter. It seems though that lochneram is the pure ethylidene isomer on the basis of cleavage with ozone. Thus if the constitution (38) is correct for C- Alkaloid T structure (40) follows for lochneram. The C p o Alkaloids.-(a) General. As work on the alkaloids of calabash- curare and Strychnos species progressed it became apparent that they fall naturally into two more or less clearly defined groups. One group contains those alkaloids which have relatively high mobilities in the solvent systems used for partition chromatography and have little or no physiological activity; all the alkaloids discussed in detail so far in this Review belong to this group.The second group contains the alkaloids with high curare activity which account for all the physiological effects of the curares or bark extracts. These alkaloids all move slowly on paper chromatograms and on cellulose partition columns. As is the case with the “fast-running” alkaloids the “slow-running” alkaloids have two nitrogen atoms in a C1,-C21 unit. One nitrogen “a) is non-basic or only weakly basic and is involved in the indole or more usually modified indole chromophore; the second N(b) is the basic or quaternary basic centre. One of the most significant advances in the chemistry of the “slow- running” highly active alkaloids came with von Philipsborn Schmid and Karrer’s demonstration that they have molecular formulz based upon C38-C40 skeletons; that is two basic or quaternary nitrogen atoms are present in the molecule.Previously all alkaloids from calabash-curare and Strychnos species had been assigned formulre based upon C,,-C21 mole- cules. The method employed by the Swiss chemists is that of partial quaternisationp2 which in this series depends upon the fact (and incidentally 41 Woodward Angew. Chem. 1956 68 13; Robinson ibid. 1957 69 40. 4a von Philipsborn Schmid and Karrer Helv. Chim. Acta 1956,39,913; cf. Battersby - and Craig J. Amer. Chem. SOC. 1951 73 1887. BATTERSBY AND HODSON CURARE ALKALOIDS 89 provides evidence for this fact) that the two basic nitrogen atoms in the tertiary base prepared from the quaternary alkaloid are sufficiently far apart for protonation or quaternisation at one basic nitrogen atom not significantly to affect either of these processes at the second basic centre.The tertiary base nor-C-curarine I obtained by pyrolysis of the quatern- ary C-curarine I chloride was treated with half an equivalent of mineral acid to give an equilibrium mixture of the species (41) (42) and (43). (46) (45) ('44) Methylation then gave a mixture of nor-C-curarine I (44 =43) monometho- nor-C-curarine I (43 and C-curarine I (46). The monometho-derivative (45) was readily separated by partition chromatography and by further methylation was converted into C-curarine I. This preparation of a C-curarine I derivative with one A@)-methyl group in each C40 unit is decisive evidence that this alkaloid has a Cpo skeleton; the molecular formula was accordingly modified to C40H44-460N4-++. By the same method C-calebassine was shownp2 to be C40H4,-,o0,N4++ and C-dihydrotoxiferine I to be C40H46N4++ and it was suggested that all the highly active calabash-curare alkaloids have CqO molecules ; this is almost certainly true.However the converse that all C40 quaternary curare alkaloids are powerful curarising agents is certainly not true as is shown by the surprisingly low activity of caracurine V dimethochloride Now it is known that the active calabash-curare alkaloids contain two quaternary centres they fall satisfyingly into place with the other quatern- ary curarising agents. Thus the bisbenzylisoquinoline alkaloids such as d-tubocurarine (47) have two quaternary nitrogen atoms set some distance apart as do the synthetic preparations such as succinylcholine (48). Indeed it is interesting from the point of view of structure-activity relations that with the structure of toxiferine I known (p.94) it turns out that the two quaternary centres are very nearly the same distance apart as those in d-tubocurarine (approximately 14 A). (b) Toxiferine I C-dihydrotoxiferine I and diaboline. During their pioneer work (1947) in the curare field Wieland Bahr and Witkopf5 isolated the highly physiologically active alkaloid toxiferine I from S. toxifera grown in British Guiana. Schmid and Karrer43 later obtained the C40H460ZN4tt (P* g5) 43 Schmid and Karrer Helv. Chim. Acta 1947 30 1162. 90 QUARTERLY REVIEWS same quaternary alkaloid from a Venezuelan calabash. Wieland’s group15 also isolated from a Venezuelan calabash preparation what they took to be a relative of toxiferine I because of the close similarity between the known and the new alkaloid’s properties.The new material was named C-dihy- drotoxiferine I although no formal relation to toxiferine I was demon- strated and it is now known that the alkaloid has been misnamed; as will be seen later C-dihydrotoxiferine I is in fact C-deoxytoxiferine I. In 0 CH,CO -0 CH2CH,’NMe CH2CO.O.CH,CH,.NMe; addition nordihydrotoxiferine I the tertiary base corresponding to the quaternary C-dihydrotoxiferine I was found by Karrer and Schmid’s groupz1 in the tertiary bases from Venezuelan S. toxifera bark. Some ten years after its isolation little was known about C-dihydro- toxiferine I. In common with toxiferine I it had been shownz0 to contain the methyleneindoline chromophore (49). Its molecular formula had been + established as C40H4sN$+ with two N-methyl groupsz1 attached to the quaternary N(b)-nitrogen atoms and ozonolysis21 had furnished acetal-.dehyde. The usual attack by various dehydrogenating agents unfortunately gave only glimpses of the molecule. Thus dehydrogenation with sulphur and with zinc dust had yielded is~quinoline;~~ distillation with zinc dust gave a mixture of 3-methyl- and 3-ethyl-indole and palladium dehydro- genation of the corresponding nor-base gave traces of a 6-carboline derivative.21 As will be discussed in the sequel C-dihydrotoxiferine I can be transformed into C-calebassine and C-curarine I both known to contain the grouping (50). In view of the production of acetaldehyde by ozonolysis of C-dihydrotoxiferine I it was taken as probable that the same quaternary allylamine system (50) also occurs in this alkaloid.In 1957 still less was known about toxiferine I but against this lack of Wieland Witkop and Bghr Annalen 1947,558 144. BATTERSBY AND HODSON CURARE ALKALOIDS 91 progress must be set the great difficulty of obtaining even a hundred milligrams of the alkaloid. von Philipsborn Schmid and KarreF2 gave evidence for a Cl0 molecule and the earlier formulae were revised to C40H46-4802N2-f+. Moreover toxiferine I had been found to undergo a change of unknown nature when treated with dilute acid; C-dihydrotoxi- ferine I behaved similarly.45 The structure of C-dihydrotoxiferine I has recently been elucidated in an outstanding series of 47 by Karrer Schmid and their collabora- tors; in addition work at Zurich and at Bristol to the structure of toxiferine I.Papers on the chemistry of these and other C40 curare alkaloids have been appearing steadily from four different laboratories and it is impossible in the space available to pay the mass of information full justice. The following account is confined to the essentials necessary for a logical presentation. Asmis Schmid and Karrer22 in 1954 isolated nine tertiary alkaloids caracurine I-IX from Venezuelan S. toxfera and in a later ~aper-4~ it was shown that caracurine V is readily transformed by dilute mineral acid into an unstable methyleneindoline base named caracurine Va. After this initial stage further acid-catalysed changes occur to give a mixture of caracurine I1 and caracurine VII both of which are stable to dilute acid. Battersby and examined the very similar changes which occur when toxiferine I also a methyleneindoline is treated with dilute acid and isolated two crystalline products.One was identical with a new quaternary alkaloid provisionally called A8 which they had i ~ o l a t e d ~ ~ . ~ ~ from S. toxfera grown in British Guiana. This alkaloid showed indoline ultraviolet absorption and the indoline nitrogen atom was proved to be secondary. Since in earlier work they had shown that Alkaloid A8 is identical with caracurine VII methochloride it follows474g that the above acid-catalysed transformations are taking place on related tertiary and quaternary molecules. Thus caracurine Va must be nortoxiferine I and the second product from toxiferine I must be caracurine I1 methochloride which was by preparing this material from authentic caracurine 11.Toxiferine I was also prepared47 by methylating caracurine Va. The set of interconversions was completed by s h o ~ i n g ~ ~ - ~ ~ that alkaloid AS in acetic acid is converted into toxiferine I in moderate yield. These transformations are summarised in the annexed scheme which includes the demonstration50 that the formation of caracurine I1 metho- chloride from toxiferine I involves atmospheric oxygen. There can be no doubt that this also holds in the tertiary caracurine Va series. 45 Asmis Bachli Schmid and Karrer Helv. Chim. Acta 1954 37 1993. 46 Bernauer Schmid and Karrer Helv. Chim. Acta 1958,41 1408. 47 Bernauer Berlage von Philipsborn Schmid and Karrer Helv. Chim. Acta 1958 49 Battersby and Hodson J. 1960 736. 41 2293. Battersby and Hodson Proc.Chem. Soc. 1958 287. Battersby and Rao unpublished work. 92 QUARTERLY REVIEWS -1 Toxiferine I 7 i' / I HOAc / Caracurine I1 / methochloride I Alkaloid A8 1 Methylate " Methylate I 1 Caracurine 11 Caracurine VII ' Caracurine Va r H,O+ Caracurine V In addition Karrer Schmid and their collaborator^^^^^^ had shown that C-dihydrotoxiferine I C40H46N4++ is converted by dilute mineral acid into the Czo alkaloid hemidihydrotoxiferine which like Alkaloid A8 had indoline ultraviolet absorption and contained NH but in addition the infrared spectrum showed the presence of an aldehyde group. As with toxiferine I a second product is also formed identical with C-Alkaloid D isolated earlier18 in Zurich from a calabash. Moreover hemidihydrotoxi- ferine in aqueous acetic acid was back into C-dihydrotoxiferine I.When these facts are combined with the knowledge that hemidihydro- toxiferine has colour reactions and an ultraviolet spectrum identical with those of Alkaloid AS and caracurine VII they leave little doubt that the interconversions summarised in the scheme below are analogous to those outlined above for toxiferine I and its nor-derivative (caracurine Va). C-Alkaloid D f HsO+ / \\ C-Dihydrotoxiferine--- 7 Hemidihydrotoxiferine \-- L HOAc A complex of inter-related alkaloids had thus been established by the foregoing experiments when the Zurich group made the important identifi- BATTERSBY AND HODSON CURARE ALKALOIDS 93 cation51 of caracurine VII with the Wieland-Gumlich aldehyde (5 1). The latter had been known for over 25 years as a degradation product obtained during H.Wieland’s studies on the structure of strychnine (52). This identification was of great interest being the first reported natural occurrence of the intermediate proposed by Woodward in his seminal biogenetic scheme for strychnine.52 OH (53) (54) A very similar biogenetic interest attaches to the tertiary base diaboline and it is convenient to leave the main theme for a moment to consider this alkaloid. It was isolated by King24 from the bark of S. diaboli and Bader Schlittler and S c h w a r ~ ~ ~ showed that it is an N(a)-acetylindoline derivative. With the structure of caracurine VII known indications derived from colour reactions and from reduction of diaboline by lithium aluminium hydride to a glycol led Battersby and H o d ~ o n ~ ~ to compare deacetyldiaboline with the Wieland-Gumlich aldehyde (5 l) and the two were identical.Thus diaboline is N(a)-acetyl-Wieland-Gumlich aldehyde (53) and its reduction product is the glycol (54). Diaboline is intermediate in complexity between Wieland-Gumlich aldehyde (5 1) and strychnine (52) and its occurrence in S. diaboli gives further support to Woodward’s biogenetic proposals. We can now return to the way in which the identification of caracurine VII as the Wieland-Gumlich aldehyde leads when combined with the above results to the structures of toxiferine I and C-dihydrotoxiferine I. Since alkaloid A8 is caracurine VII methochloride (p. 92). the former is the Wieland-Gumlich aldehyde A@)-methochloride (55) and this was rigorously confirmed;49 A8 is now better named hemitoxiferine I. Bernauer Schmid and K a r r e ~ ~ ~ proposed structure (56) for hemidihydro- 51 Bernauer Pavanaram von Philipsborn Schmid and Karrer Helv.Chim. Acta 62 Woodward Nature 1948 162 155. 59 Bader Schlittler and Schwarz Helv. Chim. Acta 1953 36 1256. 6o Battersby and Hodson Proc. Chem. Soc. 1959 126. 1958 41 1405. 94 QUARTERLY REVIEWS toxiferine i.e. that of the deoxy-Wieland-Gumlich aldehyde metho- chloride and soon afterwards this was as follows. The degrada- tion of C-dihydrotoxiferine I can be duplicated on the corresponding tertiary base nordihydrotoxiferine I to give heminordihydrotoxiferine (tertiary base corresponding to 56) which was reduced at the aldehyde function by borohydride to the primary alcohol (57). This was identical with that prepared from the Wieland-Gumlich glycol (58; R = OH) by selective bromination of the reactive allylic hydroxyl group to give the base (58; R = Br) followed by reductive removal of the halogen.We must now consider the processes by which the oxygen-free C- dihydrotoxiferine I with a methyleneindoline chromophore is formed from two molecules of the aldehyde (56) with loss of water and loss of the N(a)-hydrogen atoms. Moreover the fact that this reaction is reversed in the presence of mineral acid must be explained. The only constitution for C-dihydrotoxiferine I which satisfactorily accommodates this evidence is (59; R = H) first proposed by Bernauer Schmid and K a ~ r e r . ~ ~ Structure (60) can be written46 as aformal representation of the intermediate in both dimerisation and fission with the postulate of a double prototropic shift to move the double bond into or out of the methyleneindoline position.In the same way by combination of all the evidence outlined above the structure (59; R = OH) must be given to toxiferine I.47-49 C-Dihydrotoxi- ferine I and toxiferine I are thus examples of a new type of natural product. It remains to fit caracurine V into the picture. This base has an indoline chromophore and is readily converted into caracurine Va by dilute mineral acids or dilute acetic acid. Karrer Schmid and their co-worker~~~ have assigned to it the amino-hemiacetal structure (61) although the published chemical evidence does not exclude the alternative arrangement (62). Either of these hemiacetals would be expected readily to yield caracurine Va (nor-base corresponding to 59 R =OH) under acidic conditions.Models of the molecules (61) and (62) show that whereas the former is BATTERSBY AND HODSON CURARE ALKALOIDS 95 relatively unstrained there is considerable steric compression in the latter and on this basis the former seems much more likely. We have already mentioned that dimerisation of Wieland-Gumlich aldehyde methochloride (hemitoxiferine I) (55) with hot acetic acid gives49 a reaction mixture from which only about 20 % of toxiferine I (59; R=OH) R can be isolated directly and a similar result is obtained in buffered solu- t i ~ n . ~ ~ Caracurine V dimethochloride [61 with both N(b)-nitrogen atoms methylated] is one of the side products but the major one is 00-diacetyl- toxiferine I dichloride (59; R =OAc). Battersby and Hod~on*~ have shown that dimerisation of hemitoxiferine I (55) by means of pivalic acid (tri- methylacetic acid) in which there is strong steric hindrance of acylation gives a product from which toxiferine I (59; R=OH) can be isolated by direct crystallisation in at least 70 % yield.In contrast dimerisation of the tertiary base Wieland-Gumlich aldehyde (5 1) both in buffered aqueous acetic acid46 and in pivalic acid49 gives mainly caracurine V (61) and only a little nortoxiferine I (tertiary base corresponding to 59 R=OH). The factors controlling the various possible cyclisations are thus delicately balanced. 55 Berlage Bernauer von Philipsborn Waser Schmid and Karrer Helv. Chim. Acta 1959,42,394. 96 QUARTERLY REVIEWS An interesting but no doubt very annoying difficulty arose when the synthesis of C-diliydrotoxiferine I was attempted by Bernauer Berlage von Philipsborn Schmid and Karre~-.~~ Deoxygenation of the Wieland- Gumlichaldehyde (5 1) was achieved when the allylic hydroxyl group formed by ring-opening was replaced by bromine and the product was reduced with zinc and acetic acid.The resulting aldehyde then dimerised as expected in buffered aqueous acetic acid but though the product had colour reactions ultraviolet spectrum Rc values infrared spectrum and rotation identical with those of C-dihydrotoxiferine I it gave a picrate melting more than 60” higher than that of the natural alkaloid; the two picrates were not interconvertible. By elimination the Swiss workers were forced to conclude that this product which they designate C-dihydrotoxiferine I* is stereoisomeric with C-dihydrotoxiferine I (59; R=H) about the 19,20- and 19’,20’-double bonds.However C-dihydrotoxiferine I identical with the natural material was prepared56 from caracurine V (61) obtained in turn from the Wieland-Gumlich aldehyde (51) (see above) by reaction with hydrogen bromide to give the allylic bromide (tertiary base cor- responding to 59; R=Br) followed by reduction with zinc and acetic acid. Conversion of the final base into the corresponding methochloride gave the desired material (59; R=H). (c) C-Fhorocurarine (C-curarine III). The yellow quaternary alkaloid C-fluorocurarine was first isolated by H. Wieland Pistor and Bahr14 from a calabash-curare preparation and more recently it has been identified57 chromatographically in extracts from the bark of S. mitscherlischii. Although it has been e~tablished~~ by the partial quaternisation method (p.88) that C-fluorocurarine is a Cz0 alkaloid it is discussed in this section because of its important relations to the C40 alkaloids of the C-dihydrotoxi- ferine I “family” (p. 98). Thus both B~ekelheide’s~~ and T. Wieland’sao group have shown that C-fluorocurarine is produced by the action of concentrated hydrochloric acid on C-curarine I and Volz and T. WielandG1 obtained it by treatment of C-calebassine with the mixed anhydride of formic and acetic acid. C-Fluorocurarine has one N-methyl group on the quaternary N(b)- nitrogen atom and one C-methyl group in an ethylidene side chain. N(a)-Acetylfluorocurarine can be prepared so that the N(a)-nitrogen atom is secondary. The most striking feature of the alkaloid is however its chromophore of a kind not hitherto encountered ; its ultraviolet spectrum has a long-wavelength peak at 358 mp which undergoes a reversible bathochromic shift in the presence of alkali.With dimethyl sulphate C-fluorocurarine gives the corresponding N(a)-methyl derivative having 56 Bernauer Berlage Schmid and Karrer Helv. Chirn. Acta 1959,42,201. 57 Kebrle Schmid Waser and Karrer Helv. Chim. Acta 1953,36 345. 58 von Philipsborn Meyer Schmid and Karrer Helv. Chim. Acta 1958 41 1257. 5s Zurcher Ceder and Boekelheide J. Arner. Chem. SOC. 1958 80 1500. 61 Volz and Wieland Annalen 1957 604 1. Fritz and Wieland Annalen 1958 611 277. BATTERSBY AND HODSON CURARE ALKALOIDS 97 ultraviolet absorption identical with that of C-fluorocurarine itself but which does not show the bathochromic shift in alkali.58 Thus this shift must involve the removal of a proton from the N(a)-nitrogen of C- fluorocurarine.As the result of a masterly study of the three products obtained by borohydride reduction of N(a)-methyl-C-fluorocurarine the Zurich group suggested58 that the assembly (63) must be the chromophore of the alkaloid. The presence of an aldehyde function was confirmed by the formation of an unstable oxime and by the infrared spectrum of C-fluorocurarine which shows bands characteristic of +unsaturated /3-amino-aldehyde~.~~ By studying C-fluorocurarine and also model compounds Fritz Besch and T. Wieland62 derived the same chromophore for the alkaloid although the aldehydic nature of the carbonyl group was not recognised. However all doubt about the chromophoric system was removed by Fritz’s syn- of the aldehyde (64) the simplest compound which contains the proposed C-fluorocurarine chromophore.The absorption spectrum of this material is closely similar to that of C-fluorocurarine in neutral and in alkaline solution. It is safe then to explain the bathochromic shift in alkali as being due to generation of the mesomeric anion (66). From a consideration of its relation to C-curarine I and C-calebassine and on biogenetic grounds the Swiss proposed (65) as a hypo- thetical structure for C-fluorocurarine and this was soon confirmed by Fritz Besch and Wieland.64 Hydrogenolysis of the allylic hydroxyl group in the Wieland-Gumlich glycol (58 ; R =OH) yielded the corresponding deoxy-derivative (58 ; R =H) which underwent Oppenauer oxidation to give norhemidihydrotoxiferine (67).No details are available for the next step which involves autoxidation of the aldehyde (67) to nor-C-fluoro- curarine (tertiary base corresponding to 65) ; N(b) methylation then gave C-fluorocurarine (65) identical with the natural material. The Zurich 62 Fritz Besch and Wieland Annalen 1958 617 166. 63 Fritz Chem. Ber. 1959 92 1809. 64 Fritz Besch and Wieland Angew. Chem. 1959 71 126. 911 QUARTERLY REVIEWS group provided independent proof65 from another angle; they reduced C-fluorocurarine to norhemidihydrotoxiferine (67) which was then dimerised as described earlier to yield C-dihydrotoxiferine I (59; R=H). Since the structure of C-dihydrotoxiferine I has been related chemically to that of the Wieland-Gumlich aldehyde C-fluorocurarine must have the constitution (65).Several important reactions have been described by various workers which show that many of the calabash- curare and Strychnos alkaloids can be grouped together in so-called “families” containing mutually related alkaloids. Thus when solid C- dihydrotoxiferine I is irradiated in the presence of oxygen it is converted into C-curarine I whereas C-calebassine is formed when the irradiation is carried out in solution containing eosin as a sensitiser. The formation of C-alkaloid D from C-dihydrotoxiferine I under acidic conditions was mentioned earlier (p. 92) as was the production of C-fluorocurarine by degradation of C-curarine and C-calebassine (p. 96). These reactions are summarised in the annexed chart. (d) The “jiarnilies” of alkaloids. C-Alkaloid D iH*o+ ref.48 Oz hv ref. 66 C-Dihydrotoxiferine I -+ C-CurarineI Conc. HC1 refs. 60 59 I 02 pyridine HoAc ref. 67 HCO.OAc ref. 61 C-Calebassine -- -+ C-Fluorocurarine Inter-relations in the C-dihydrotoxiferine I “family”. A similar scheme was established for alkaloids related to toxiferine I and there can be no doubt that the corresponding fundamental changes involved in the two families are strictly analogous. Thus C-Alkaloid E in the toxiferine I “family” corresponds to C-curarine I in the C-dihydro- toxiferine I “family” ; C-Alkaloid A corresponds to C-calebassine and caracurine I1 methochloride to C-Alkaloid D. In passing it is worth noting the recent work1’ on King’s alkaloidsls which has shown that caracurine I1 methochloride and C-Alkaloid A can be isolated from the bark of S.toxifera. The separation of C-Alkaloid A is the first example of 65 von Philipsborn Bernauer Schmid and Karrer Helv. Chim. Actu 1959,42 461. 66 Bernauer Schmid and Karrer Helv. Chim. Actu 1957,40 1999. 67 Asmis Schmid and Karrer Helv. Chim. Actu 1956 39 440. BATTERSBY AND HODSON CURARE ALKALOIDS 99 an alkaloid of the C-calebassine type to be isolated in substance from a plant; all previous isolations of this type of alkaloid and those of the C-curarine I type have been from calabash-curare preparations which have undergone largely unknown treatments by their native manufacturers.1° Caracurine I1 methochloride &O+ 0 2 refs. 49 50 01 hv -+ C-Alkaloid E C-Toxiferine I - ref. 68 1 0 2 pyr’dine pivalic HOAc (ref. 69a) acid or /%ti J. C-Alkaloid A Inter-relations in the toxiferine I “family”.The analogue of C-fluorocurarine in the toxiferine I family has not so far been isolated from natural sources. It would have the structure (68) or perhaps less probably the hemiacetal form (69); attempts to make it by oxidation of the Wieland-Gumlich aldehyde (51) both at Bristolsg and at Berlage Bernauer Schmid and Karrer have recently69a proved that C-Alkaloid H is the toxiferine-like mixed condensation product of Wieland-Gumlich aldehyde methochloride (hemitoxiferine I) and its 18- deoxy-derivative (hemidihydrotoxiferine) which gives constitution (70) for C-Alkaloid H. The tertiary caracurine VI is said to be the nor-base from this “hybrid” and it has been shownsga that C-Alkaloids F and G are respectively the C-calebassine and the C-curarine analogue in this ‘‘family”.have so far been unsuccessful. Bernauer Berlage Schmid and Karrer Helv. Chim. Acta 1958 41 1202. e9 Battersby and Hodson unpublished work. 60a Berlage Bernauer Schmid and Karrer Helv. Chim. Acta 1959,42 2650. Professor H. Schmid personal communication. 100 QUARTERLY REVIEWS The key position of the Wieland-Gumlich aldehyde (51) in this group of alkaloids is now obvious. From this compound its 18-deoxy-derivative and their N(b)-metho-derivatives can be derived no fewer than nineteen* of the tertiary and quaternary alkaloids isolated from calabash-curares and the barks of South American Strychnos species. (e) C-Curarine I and C-calebassine. No structures have yet been pro- posed for C-curarine I and C-calebassine which were the first properly characterised alkaloids to be isolated from calabash-curare.12* l3 The photo- oxidation of C-dihydrotoxiferine I C40H46N4++ (59; R=H) to give C- curarine I C40H44-460N4++ has already been mentioned (p.98) and the oxygen atom introduced is presumably in an ether linkage. Little help comes from the ultraviolet absorption of C-curarine I which was earlier a t t r i b ~ t e d ~ ~ ~ ~ ~ ~ ~ ~ to an indolenine chromophore (71) but is now thought to be of a unique type;1° however it is worth noting that the spectrum is very similar to that of the amino-hemiacetal caracurine V (61). The early chemical investigations showed that C-curarine I gives acetaldehyde on ozonolysis and that it contains the system (72). von Philipsborn Schmid and K a r ~ e r ~ ~ recognised that this undergoes an * Caracurine VII hemitoxiferine I C-fluorocurarine diaboline toxiferine I C- dihydrotoxiferine I nordihydrotoxiferine caracurine V C-Alkaloid A C-Alkaloid E caracurine I1 methochloride caracurine 11 C-calebassine C-curarine I C-Alkaloid D C-Alkaloid H C-Alkaloid F C-Alkaloid G.caracurine VI 71 Schmid and Karrer Angew. Chem. 1955,67 361. 72 Karrer Bull. SOC. chim. France 1958 99. 73 von Philipsborn Schmid and Karrer Helv. Chim. Acta 1955 38 1067. BATTERSBY AND HODSON CURARE ALKALOIDS 101 interesting vinylogous Hofmann elimination as indicated when it is attacked by alkali to give a bis-tertiary base containing two diene residues (partial structure 73). Hydrogenation of the latter gave the corresponding octahydro-derivative (partial structure 74) which yielded wmethylbutyric acid (75) when oxidised by the modified (micro-)Kuhn-Roth method;74 this was the first application in the alkaloid field of a technique which has since been widely used.A major clue concerning the structure of this alkal- oid comes from its degradation to C-fluorocurarine (65) by the action of concentrated hydrochloric acid,69* 6o but much more experimental informa- tion will be required before even reasonable working hypotheses can be formulated. That there may be considerable difficulties ahead is indicated by the experiments of Boekelheide et al.75 on the Hofmann degradation of C-curarine I which are considered by the authors to point to an unsym- metrical structure for the alkaloid. It looks at present as though C-curarine I the first calabash-curare alkaloid to be crystallised may well represent the most difficult structural problem in the field.C-Calebassine C40H4802N2++ also contains two of the systems (72) but unlike C-curarine I it does not undergo vinylogous Hofmann elimina- tion; however the +NMe(b)-CH bonds can be reductively cleaved over platin~m.'~ The alkaloid contains two oxygen atoms more than C- dihydrotoxiferine I and they are present as hydroxyl groups. Evidence for their carbinolamine nature [ >-&(OH)-] comes from their reductive removal by zinc and acetic acid to yield deoxy-C-~alebassine~~ which can be reconverted into C-calebassine by photo-oxidation.68 Bernauer Schmid and Karrer78 provided further support for two carbinolamine systems by showing that a dimethyl ether can be formed from C-calebassine by treat- ment with dry methanolic acid. This ether formation is readily reversed in dilute aqueous acid at room temperature.Tetrahydro-C-calebassine in which both ethylidene side chains of the two groupings (72) have been reduced forms an analogous dimethyl ether.78 It is certain that the hydroxyl groups are intimately connected with the chromophore of the alkaloid since the ultraviolet spectra of C-calebassine and of tetrahydro-C-calebassine undergo a shift of some 10 mp in alkaline solution that is not shown by the corresponding dimethyl ethers. Indeed the alkali-induced shift is held33 to be diagnostic for the 2-hydroxyindoline chromophore (as in 76). Further removal of the hydroxyl groups to form the deoxy-derivative increases the basicity of the N(a)-nitrogen atoms and perhaps in addition increases their steric accessibility such that a N(a) N(b),N(b)-trimethyl derivative can be formed by the action of methyl 74 Garbers Schmid and Karrer Helv.Chim. Acta 1954 37 1336. 75 Boekelheide Ceder Natsume and Zurcher J. Amer. Chem. SOC. 1959 81 2256. 76 Bernauer Schmid and Karrer Helv. Chim. Acta 1957,40 731. 77 Volz and Wieland Naturwiss. 1957 44 376. Bernauer Schmid and Karrer Helv. Chim. Acta 1958 41 673. 102 QUARTERLY REVIEW5 iodide on deoxy-C-calebassine at elevated temperature^.'^ Incidentally this gives further proof of the Cpo nature of this alkaloid. The non-forma- tion of a tetra-N-methyl derivative from deoxy-C-calebassine can readily be rationalised in terms of the field effect and probably steric effect also of what is presumably the closely placed quaternary N(a)-atom; this is in contrast to the relatively large distance between the N(b)-atoms noted earlier.2CI - - r C22H32 Thus it is possible to write79 the partial structure (76) for C-calebassine and illustrate the formation of the trimethyl derivative (78) from deoxy- C-calebassine (77). In lowacid the ultraviolet spectra of C-calebassine and its tetrahydro- derivative show peaks at ca. 320 mp indicating extended conjugation. This is interpreted by the Zurich in terms of the partial structure (79) for the alkaloid which in strong acid reversibly gives the mesomeric cation We have mentioned earlier (p. 98) the relation of C-calebassine to C-fluorocurarine and also the formation of C-calebassine by photo- oxidation of C-dihydrotoxiferine I. The latter oxidation can also be achieved68 under acid-base catalysis (pyridine-acetic acid) in presence of oxygen.With this knowledge of its close relation to C-dihydrotoxiferine I it is tempting to fit the partial structure (79) into the C-dihydrotoxiferine I skeleton to give constitution (8 1) for C-calebassine. However this is unlikely on a number of grounds particularly the stability of deoxy-C- calebassine towards acids ;lo the analogue in the toxiferine I “family” namely deoxy-C-Alkaloid A is also stable under strongly acidic condi- t i o n ~ . ~ ~ (80). 7 9 Bernauer Schmid and Karrer Helv. Chim. Acta 1958,41 26. BATTERSBY AND HODSON CUKARE ALKALOIDS 103 ItH’ The structures of C-curarine and C-calebassine and those of their hydroxy-analogues C-Alkaloid E and C-Alkaloid A represent the major challenge at present to chemists working in this field; no less interesting are the structures of C-Alkaloid D and caracurine I1 methochloride formed under such mild conditions from the methyleneindoline alkaloids.How- ever even when these problems are solved there remains much to do in this difficult field as the Appendix makes amply clear. APPENDIX The following alkaloids of unknown structure (not listed in the Table on p. 81) have been isolated from calabash-curare or Strychnos species C-Guianine;80 C-Alkaloids Q R and S C-Alkaloid X;28 C-curarine 11 ;13* 78 C-isodihydrotoxiferine ;15 C-Alkaloids B C I J UB and L;18 C-Alkaloids M 0 and P;23980 caracurine I 111 and IV;22 caracurine VIII and IX methochlorides;21 melinonine E H I K L and M;29 C-fluoro- curinine ;Is pseudofluorocurine xanthocurine fedamazine ;22 C-cale- bassinine ;I8 alkaloids 1 and 2;19 toxiferine 11 ;44 croceocurine ;82 macro- phylline-A ;83 kryptocurine ;82 toxiferine 111 VIII and XII ;16J7 macusine A and B.17 *O Giesbrecht Meyer Bachli Schmid and Karrer Helv. Chim. Acta 1954,37,1974. 81 Meyer Schmid and Karrer Helv. Chim. Acta 1956 39 1208. 83 Iorio Corvillon Alves and Marini-Bettolo Gazetta 1956 86 923. Meyer Schmid Waser and Karrer Helv. Chim. Acta 1956 39 1214.

ISSN:0009-2681    

DOI:10.1039/QR9601400077

出版商:RSC    

年代:1960

数据来源: RSC

摘要:

ERRATA 1960 Vol. 14 Page 4 262 265 294 295 296 303 308 314 Ref. 18. The authors should be Clauss Plass Boehm and Hofmann. First line after eqn. (12). For Hi = j’ #i H #i and& = $ $C H $ C read Hi = $ #i H $id7 and Hc = J $c H &dT. Second line after eqn. (1 7). For resonance read cohesive. Ref. 14 should read Lauger Martin and Miiller Helv. Chim. Acta 1944 27 892. Ref. 25. For 1914 read 1913. Ref. 31 should read Haynes and Plimmer Chem. and Ind. 1954 1147. Ref. 62. For 326 read 3495. Third line after formula (42). For pK read pKa. Ref. 90 should read Lecoq Bull. SOC. chim. France 1951,18 183.

ISSN:0009-2681    

DOI:10.1039/QR9601400454

出版商:RSC    

年代:1960

数据来源: RSC

摘要:

CUMULATIW INDEXES VOLUMES I-XIV (1947-1960) CUMULATIVE INDEX OF AUTHORS Abrahams S. C. 10,407 Abrikosova I. I. 10,295 Addison C. C. 9 11 5 Ahrland S. 12 265 Albert A. 6 197 Allen G. 7 255 Amphlett C. B. 8 219 Anderson J. S 1 331 Angyal S. J. 11 212 Arnstein H. R. V. 4,172 Atherton F. R. 3 146 Avison A. W. D. 5 171 Bacon R. G. R. 9 287 Baddeley G. 8 355 Baddiley J. 12 152 Badger G. M. 5 147 Bagnall K. W. 11 30 Baker W. 11 15 Baltazzi E. 9 150 Barker S. A. ,7 58 Barltrop J. A. 12 34 Barnartt S. 7 84 Barrer R. M. 3 293 Barton D. H. R. 3 36; 10,44; 11 189 Bassett H. 1 247 Bateman L. 8 147 Battersby A. R. 14 77 Baughan E. C. 7 103 Baulch D. L. 12 133 Bayliss N. S. 6 319 Bell R. P. 1 113; 2 132; 13 169. Bentley R. 4 172 Bergel F. 2 349 Bethell D. 12 173 Bevington J. C. 6 141 Birch A.J. 4,69; 12 17 Bircumshaw L. L. 6 Bockris J. O’M 3 173 Bolland J. L. 3 1 Bond G. C. 8 279 Bourne E. J. 7 58 Bowen E. J. 1 1 ; 4,236 Bradley R. S. 5 315 Braude E. A. 4,404 Bremner J. G. M. 2 1 Brink N. G. 12 93 Brown B. R. 5 131 Brown R. D. 6 63 Buchanan J. G. 12,152 157 Buckingham A. D. 13 Bu’Lock J. D. 10 371 Bunnett J. F. 12 1 Burkin A. R. 5 1 Burnett G. M. 4 292 Burton H. 6 302 183 Cadogan J. I. G. 8 308 Caldin E. F. 7 255 Carrington A, 14 427 Challenger F. 9 255 Chatt J. 12 265 Coates G. E. 4 217 Collins C. J. 14 357 Collinson E. 9 31 1 Cook A. H. 2 203 Cook J. W. 5 99 Cookson R. C. 10,44 Cooper C. F. 13 71 Cottrell T. L. 2 260 Coulson C. A. 1 144 Cowdrey W. A. 6 358 Cox E. G. 7 335 Crawford V. A. 3 226 Croft R. C. 14 1 Crofts P. C. 12 341 Crombie L. 6 101 Cross A. D. 14 317 Cruickshank D.W. J. Curran S. C. 7 1 Cuthbert J. 13 215 14 378 7 335 Dainton F. S. 12 61 Dalgliesh C. E. 5 227 Davies A. G. 9 203 Davies D. S. 6 358 Davies M. 8 250 Davies N. R. 12 265 Davies R. O. 11 134 Dawton R. H. V. M. De Heer J. 4 94 de la Mare P. B. D. 3 de Mayo P. 11 189 Derjaguin B. V. 10,295 Dickens P. G. 11 291 Doyle W. T. 14 62 Dubinin M. M. 9 101 456 9 1 126 Duncan J. F. 2 307; Dunning W. J. 9 23 12 133 Eastham J. F. 14 221 Eley D. D. 3 181 Emelkus H. J. 2 132 Errede L. A. 12 301 Evans M. G. 4 94 6 Evans R. M. 13 61 186 Fensham P. J. 11 227 Ferrier R. J. 13 265 Foster A. B. 11 61 Freidlina R. Kh. 10 330 Gascoigne R. M. 9,328 Gaydon A. G. 4 l Gee G. 1 265 Gent W. L. G. 2 383 Gibson D. T. 3 263 Gillespie R. J. 2 277 Gilman H. 13 116 Glenn A. L. 8 192 Goehring M. 10 437 Gold V.9 51 ; 12 173 Gowenlock B. G. 12 321,14 133 Gray P. 9 362 Greenwood N. N. 8 1 Griffith J. S. 11 381 Gundry P. M. 14 257 Gunstone F. D. 7 175 Gutmann V. 10 451 8,40; 11 339 Halpern J. 10,463 Hamer F. M. 4 327 Hardy D. V. N. 2 25 Harman R. E. 12 93 Harris M. M. 1 299 Hartley G. S. 2 154 Hassel O. 7 221 Hawkins E. G. E. 4 Hawkins J. D. 5 171 Haynes L. J. 2 46; 14 Heaney H. 11 109 Hey D. H. 8 308 25 1 292 CUMULATIVE INDEX 457 Hickling A. 3 95 Hochstrasser R. M. 14 Hodson H. F. 14,77 Holt R. J. W. 13 327 Hughes E. D. 2 107; 5 245; 6 34 Hush N. S. 6 186 146 Ingold C. K. 6 34; Irving H. M. 5 200 Ivin K. J. 12,61 11 1 Jacobs P. W. M. 6,238 Jain A. C. 10 169 Janz G. J. 9 229 Jeffrey G. A, 7 335 Jenkins E. N. 10 83 Jennings K. R. 12 116 Jones D. G. 4,195 Kapustinskii A. F. 10 Katritzky A.R. 10 Kenyon J. 9 203 Khorana H. G. 6 340 Kipling J. J. 5,60; 10 1 Kitchener J. A. 13 71 283 395; 13 353 Lagowski J. J. 13,233 Lamb J. 11 134 Lamberton A. H. 5 75 Law H. D. 10,230 Lea F. M. 3 82 Leech H. R. 3 22 Leisten J. A. 8 40 Levy N. 1 358 Lewis E. S. 12 230 Lewis J. 9 11 5 Lifshitz E. M. 10 295 Linnett J. W. 1 73; 11 291; 12,116 Lister B. A. J. 2 307 Lister M. W. 4 20 Livingston R. 14 174 Long L. H. 7 134 Longuet-Higgins H. C. 11 121; 14 427 Loudon J. D. 5 99 Luttke W. 12 321 Lythgoe B. 3 181 Maccoll A. 1 16 McCoubrey J. C. 5 MacDiarmid A. G. 10 McGrath W. D. 11 87 McKenna J. 7 231 McLaughlin E. 14,236 Maddock A. G. 5 270 Maitland P. 4 45 Manners D. J. 9 73 Marsh J. K. 1 126 Martin F. S. 13 327 Martin R. L. 8 1 Megson N. J. L. 2 25 Millar 1. T. 11 109 Millen D. J. 2 277 Morgan K.J. 8 123; Morrison A. L. 2 349 Musgrave W. K. R. 8 364; 11 87 208 12,34 331 Nancollas G. H. 14 Nelson Smith R. 13 Nesmeyanov A. N. 10 Newth F. H. 13 30 Norrish R. G. W. 10 Nyholm R. S. 3 321; 402 257 330 149 7,377; 11,339 Ollis W. D. 11 15 Orgel L. E. 8 422; 11 Orville-Thomas W. J. Overend W. G. 11 61; Owston P. G. 5 344 Page J. E. 6 262 Paneth F. A. 2 93 Parsonage N. G. 13 Pauson P. L. 9 391 Pepper D. C. 8 88 Percival E. G. V. 3,369 Phillips F. C. 1 91 Plimmer J. R. 14 292 Pople J. A. 11 273 Porter G. B. 14 146 Praill P. F. G. 6 302 Pritchard H. O. 14 46 38 1 11 162 13,265 306 Reid C. 12 205 Richards R. E. 10 480 Riddiford A. C. 6 157 Riley H. L. 1,59; 3,160 Rose J. D. 1 358 Rowlinson J. S. 8 168 Satchell D. P. N. 9 51 Saxton J. E. 10 108 Schofield K. 4 382 Selman S. 14 221 Seshadri T.R. 10 169 Sexton W. A. 4 272 Sharpe A. G. 4 115; Shchukina L. A. 10 Sheldon J. C. 14,200 Shemyakin M. M. 10 Sheppard N. 6 1 ; 7 19 SillCn L. G. 13 146 Simes J. J. H. 9 328 Simons P. 13 3 Simpson D. M. 6 1; 7 Smales A. A, 10 83 Smith B. C. 14 200 Smith H. 12 17 Smith J. A. S. 7 279 Smith M. L. 9 1 Springall H. D. 10 230 Stacey M. 1 179 213 Staveley L. A. K. 3,65; Stern E. S. 5 405 Stone F. G. A. 9 174 Sutton L. E. 2 260 Swallow A. J. 9 31 1 Symons M. C. R. 12 230 13. 99 14. 62 11,49 261 26 1 19 13,306 Synge; R.>L. M. 3 245 Szwarc M. 5 22; 12 301 Taylor A. W. C. 4 195 Tedder J. M. 14 336 Thomas S. L. 7 407 Thomson R. H. 10,27 Thrush B. A. 10 149 Tipper C. F. H. 11 313 Tomkins F. C. 6 238 Tompkins F. C. 14,257 Topley B. 3 345 Trapnell B. M. W. 8 404 458 QUARTERLY REVIEWS Trotrnan-Dickenson A.Truter E. V. 6,390 Turner E. E. 1 299 Turner H. S. 7 407 F. 7 198 Ubbelohde A. R. 4 356; 5 364; 11,246 Ulbricht T. L. V. 13,48 Uri N. 6 186 Vainshtein B. K. 14 105 Walsh A. D. 2 73 Warburton W. K. 8,67 Warhurst E. 5 44 Waters W. A. 12 277 Weedon B. C. L. 6 380 Wells A. F. 2 185; 8 Wells R. A. 7 307 380 Whiffen D. H. 4 131; Whytlaw-Gray R. 4. Wilson H. N. 2 1 Wittenberg D. 13 116 Woodward L. A. 10 12,250 153 185 Yoffe A. D. 9 362 Zakharkin L. I. 10,330 CUMULATIVE INDEX OF TITLES Acetylenes as natural products 10 37 1 Acetylenes infrared and Raman spectra of 6 1 Acid use of the term 1 11 3 Acids carboxylic anodic syntheses with 6 380 Acids carboxylic associa tion of 7 25 5 Acids straight-chain fatty natural and synthetic recent developments in the preparation of 7 175 Acids tetronic 14 292 Acid-base reactions simple rates of 13 169 Addition reactions free-radical of olefinic systems 8 308 Adsorption of non-electrolytes from solution 5,60 Affinities relative of ligand atoms for acceptor molecules and ions 12,265 Age geological determination of by radioactivity 7 1.Aldehydes polymerisation of 6 141 Aliphatic compounds saturated inter- action of free radicals with 14 336 Alkaloids of calabash-curare and Stt-ychnos species 14 77 Alkaloids ergot 8 192 Alkaloids indole excluding harmine and strychnine 10 108 Alkaloids steroidal 7 231 Alkaloids veratrum 12 34 Alkanes infrared and Raman spectra Alkanes tetra- and tri-chloro- and Analgesics synthetic 2 349 Analysis conformational principles of 10 44 Analysis inorganic applications of solvent extraction to 5 200 Analysis radioactivation 10 83 Anionotropy 4,404 Anodic syntheses with carboxylic acids 6,380 Antibiotics newer chemistry of 12.93 Arrheniua factors (frequency factors) in unimolecular reactions 14 133 Aspects physicochemical of some recent work on photosynthesis 14 174 Association of carboxylic acids 7,255 of 7 19 related compounds 10 330 Asymmetry the non-conservation of parity and optical activity 13 48 Attraction molecular direct measure- ment of between solids separated by a narrow gap 10,295 Base use of the term 1 113 Benzilic acid and related rearrange- ments 14 221 Biological reactions r61e of phosphoric esters in 5 171 Bond aromatic 5 147 Bond chemical in crystals applica- tion of electron diffraction to the study of 14,105 Bonding chemical and nuclear quad- rupole coupling 11,162 Bonds dissociation energies of 5 22 Bonds interpretation of properties of Borazoles the 14 200 Boron hydrides chemistry of 9 174 Boron hydrides and related com- Boron trifluoride co-ordination corn- 2 260 pounds 2 132 pounds of 8 1 Carbides of iron 3 160 Carbohydrate epoxides 13 30 Carbohydrate phosphates 11 61 Carbohydrate sulphates 3 369 Carbohydrates newer aspects of stereochemistry of 13 265 Carbon amorphous and graphite 1 59 Carbon and oxygen surface corn- pounds of 13 287 Carbon-carbon bonds oxidative hydrolysis of in organic molecules 10 261 Carbon-carbon double bonds geo- metriyal isomerism about 6 101 Carbon-hydrogen bond polarity of 2 383 Carbon-hydrogen bonds mechanism of breakage of 12 230 Carbon-phosphorus bonds com- pounds containing 12 341 Carbonitrides of iron 3 160 Carbonium ions structure of 12,173 Carbons active study of porous structure of by a variety of methods 9,101 459 460 QUARTERLY REVIEWS Carbons adsorbent properties and nature of 10 1 Carbonyls of metals chemistry of 1 33 1 Catalysis by metals specificity in 8 404 Catalysis of reactions involving hydro- gen mechanisms of 3,209 Catalysis and semiconductivity 11 227 Catalysts redox initiation of poly- merisations by 9 287 Cations organic reactions of 6 302 Charcoals active study of porous structure of by a variety of methods 9 101 Chemisorption of gases on metals 14 257 Chromatography inorganic 7 307 Chromium mechanisms of oxidation by compounds of 12 277 Collisions in gases energy transfer in 11 87 Colloidal electrolytes state of solution of 2 154 Colour and constitution 1 16 Colour centres in alkali halide crystals 14 62 Combustions slow in the gas phase elementary reactions in 11 313 Complex compounds stabilities of 5 l Conductance ionic in solid salts 6 238 Configuration of flexible organic molecules 5 364 Conformational analysis principles of 10 44 Conjugated compounds free-electron approximation for 6 319 Co-ordination compounds of boron trifluoride 8 1 Crystal structure and melting 4 356 Crystal structures of salt hydrates and complex halides 8 380 Crystalline transition-metal com- pounds electron resistance in 14,427 Crystals alkali halide colour centres in 14 62 Crystals chemical bonds in applica- tion of electron diffraction to the study of 14 105 Crystals location of hydrogen atoms in 10 480 Crystals ionic lattice energy of 10 283 Cyanine dyes 4 327 Cyclohexane stereochemistry 221 of 7 Decarboxylation thermal mechanism Degradation biological of trypto- Densities limiting 4 153 Dielectric absorption 8 250 Dihalogen compounds Grignard and organolithium compounds derived from 11 109 Disproportionation in inorganic com- pounds 2 1 Diterpenoids chemistry of 3 36 Dyes effect of light on 4 236 Dyes cyanine 4,327 Dyes organic and their constitution of 5 131 phan 5 227 1 16 Earth distribution of the elements in the 3 263 Electrode processes in aqueous solu- tions mechanism of 3 95 Electrolytes effects of ultrasonic waves on 7 84 Electrolytes colloidal state of solu- tion of 2 154 Electromagnetic separation of stable isotopes 9 1 Electron correlation and chemical consequences 11 291 Electron resistance in crystalline trans- ition-metal compounds 14 427 Electrons structures of molecules deficient in 11,121 Elements terrestrial distribution of 3 263 Elements heavy radioactivity of 5 270 Elements of Group VITI recent stereochemistry of 3 321 Elements of Groups IVB and IV comments on the thermochemistry of 7 103 Elements of the rare-earth series separation of 1 126 Elements transuranic chemistry of 4 20 Energy transfer of in gaseous collisions 11 87 Enzymes degradation of polysacchar- ides by 9 73 CUMULATIVE INDEX 46 1 Enzymes synthesis of polysaccharides Epoxides of sugars 13 30 1,2-Epoxides naturally-occurring the chemistry of 14 317 Equilibria hydrolytic quantitative studies of 13 146 Equivalent-orbital approach to mole- cular structure 11 273 Ergot alkaloids structure of 8 192 Esters carboxylic and related com- pounds alkyl-oxygen heterolysis in 9,203 Exchange reactions of hydrogen iso- topes in solution principles of 9 51 Extraction liquid-liquid in inorganic chemistry 13 327 by 7 58 Ferrocene and related compounds 9 Flames emission spectra of 4 1 Flash photolysis and kinetic spectro- scopy 10 149 Flavones nuclear methylation of 10 169 Fluorescence and fluorescence quench- ing 1 1 Fluorine laboratory and technical production of 3 22.Fluorine compounds general aspects of the inorganic chemistry of 11,49 Fluorine compounds laboratory and technical production of 3 22 Fluorine compounds organic reac- tions of 8 331 Foaming current concepts in theory of 13 71 Force constants 1 73 Forces intermolecular and the pro- perties of matter 8 168 Free-electron approximation for con- jugated compounds 6 319 Friedel-Crafts reaction modern aspects of 8 355 Furans some aspects of the chemistry of 4 195 391 Gases adsorbed infrared spectra of Gases chemisorption of on metals Gases elementary reactions in slow Gases energy transfer in collisions in 14 378 14 257 combustions in 11 313 11 87 Graphite and amorphous carbon 1 Graphite lamellar compounds of Grignard reagents derived from di- 59 14 1 halogen compounds ll 109 Halide alkali crystals colour centres in 14 62 fialides reactions of in solution 5 245 Halides complex crystal structures of 8 380 Halogens kinetics of thermal addition of to olefins 3 126 Heats of formation of simple in- organic compounds 7 134 Heteroaromatic compounds infrared spectra of 13 353 Heterogeneous reactions transport control in 6 157 Heterolysis alkyl-oxygen in carbo- xylic esters and related compounds 9 203 Hydrocarbons infrared and Raman spectra of.Part I acetylenes and olefins 6 1. Part 11 paraffins 7 19 Hydrogen molecular homogeneous reactions of in solution 10 463 Hydrogen atoms location of in crystals 10,480 Hydrogen catalysis mechanisms of 3 209 Hydrogen isotope exchange reactions in solution principles of 9 51 Hydrogen peroxide its radicals and its ions energetics of reactions involving 6 186 Hydrogenation catalytic and related reactions mechanism of 8,279 Hyperconjugation 3 226 Ice structure of 5 344 Immunochemistry aspects of 1 179 Indole alkaloids excluding harmine Induction asymmetric and asym- Infrared spectra of adsorbed gases 14 Inorganic chemistry and magnetism Inorganic compounds disproportiona- 21 3 and strychnine 10 108 metric transformation 1,299 378 7 377 tion in 2 l 462 QUARTERLY REVIEWS Inorganic compounds Raman spectra Inorganic compounds stereochemistry of 11,339 Inorganic compounds simple heats of formation of 7 134 Inositols 11 212 Insecticides synthetic structure and activity in 4 272 Interaction of free radicals with saturated aliphatic compounds 14 336 Tnterhalogen compounds and poly- halides 4,115 Intermolecular forces and some pro- perties of matter 8 168 Iodine compounds inorganic some reactions of 8 123 Ion association in aqueous solution thermodynamics of 14 402 Ion exchange 2 307 Ionisation potentials and far ultra- violet spectra their significance in chemistry 2 73 Iron carbides nitrides and carbo- nitrides of 3 160 Isoflavones 8 67 Isomerism geometrical about carbon- carbon double bonds 6 101 Isotopes exchange of between different oxidation states in aqueous solution 8 219 Isotopes synthesis of organic com- pounds labelled with 7 407 Isotopes tracer techniques involving 4,172 Isotopes stable electromagnetic separation of 9 1 of 10 185 Lactones physiologically active un- saturated 2 46 Lamellar compounds of graphite 14 1 Lanthanons separation of 1 126 Lattice energy of ionic crystals 10 283 Ligand atoms relative affinities of for acceptor molecules and ions 12 265 Ligand-field theory 11 381 Light absorption of and photo- chemistry 4,236 Liquids transitions in 3 65 Liquids transport properties of in relation to their structure 14 236 Liquids ultrasonic analysis of relaxa- tion processes in 11 134 Magnetic resonance absorption Magnetism and inorganic chemistry Manganese mechanisms of oxidation Manganese dioxide oxidations by in Mass spectrometry application of to Mass spectrometry of free radicals 13 Melting and crystal structure 4 356 Meso-ionic compounds 11 15 Metal-amine solutions reduction by; applications in synthesis and deter- mination of structure 12 17 Metal-ammonia solutions reduction of organic compounds by 4 69 Metal-transition compounds crystal- line electron resistance in 14 427 Metals chemisorption of gases on 14 257 Metals nature of solutions of 13 99 Metals specificity in catalysis by 8 Methyl radicals reactions of 7 198 Methylation biological 9 255 Methylation nuclear of flavones and related compounds 10 169 Molecules determination of structure of by X-ray crystal analysis modern methods and their accuracy 7 335 Molecules molecular-orbital and equivalent-orbital approach to structure of 11 273 Molecules electron deficient struc- tures of 11 121 Molecules electronically excited reac- tions of in solution 13 3 Molecules flexible organic configura- tion of 5 364 Molecules organic oxidative-hydro- lysis of carbon-carbon bonds in 10 26 1 Molecules simple representation of by molecular orbitals 1 144 Molecular-orbital approach to mole cular structure 11 273 Molecular-sieve action of solids 3 293 nuclear 7 279 7 377 by compounds of 12,277 neutral media 13 61 chemical problems 9 23 21 5 404 CUMULATIVE INDEX 463 Morphine synthetic approaches to structure of 5,405 Nitramines some aspects of the chemistry of 5 75 Nitration of aromatic compounds 2 277 Nitration of heterocyclic nitrogen compounds 4,382 Nitrides of iron 3 160 Nitro-compounds aliphatic 1 358 Nitrogen active 12 116 Nitrogen compounds heterocyclic nitration of 4 382 Nitrogen dioxide-dinitrogen tetroxide system structure and reactivity of 9 362 C-Nitroso-compounds structure and properties of 12 321 Nitrosyl group chemistry of 9 115 Non-electrolytes adsorption of from solution 5,60 Non-electrolytes theories of solutions of 13 306 Nuclear chemistry quantitative 12 133 Nuclear magnetic resonance absorp- tion 7,279 Nuclear quadrupole coupling and chemical bonding 11 162 Nucleation in phase changes 5 315 Nucleotide coenzymes recent develop- ments in biochemistry of 12 152 Oceans salt deposits from 1 91 Olefinic systems fresradical addition reactions of 8,308 Olefins infrared and Raman spectra of 6 1 Olefins kinetics of oxidation of 3 1 Olefins kinetics of thermal addition of halogens to 3 126 Olefins oxidation of 8 147 Optical activity and non-conservation of parity 13,48 Orbitals molecular approach to mole- cular structure through 11 273 Orbitals molecular and organic reactions 6 63 Orbitals molecular representation of simple molecules by 1 144 Organic compounds action of ionising radiations on 9 31 1 Organic compounds behaviour of in sulphuric acid 8 40 Organic compounds estimation of thermodynamic properties for 9 229 Organic compounds polarography of 6 262 Organic compounds reduction of by metal-ammonia solutions 4,69 Organic compounds isotopically labelled synthesis of 7 407 Organic reactions and molecular orbitals 6 34 Organolithium reagents derived from dihalogen compounds 11 109 Organometallic compounds of the first three periodic groups 4,217 Organosilylmetallic compounds for- mation and reactions of 13 116 5-Oxazolones chemistry of 9 150 Oxidation by compounds of chro- mium and manganese mechanisms of 12 277 Oxidation of olefins 3 1 ; 8 147 Oxidation-reduction potential of quinones relation of to chemical structure 4 94 Oxides of metals structures of 2 185 N-Oxides aromatic heterocyclic chemistry of 10 395 Oxygen and carbon surface com- pounds of 13,287 Parity non-conservation of 13 48 Penicillins chemistry of 2,203 Peptides methods of synthesis and terminal-residue studies of 10 230 Peptides structural investigation of 6,340 Peptides naturally occurring 3 245 Perfluoroalkyl derivatives of metals and non-metals 13,233 Peroxides organic and their reactions 4,251 Phase changes nucleation in 5 315 Phenols tautomerism of 10 27 Phosphates of carbohydrates 11 61 Phosphates condensed 3 345 Phosphoric esters r81e of in biological reactions 5 171 Phosphorus oxyacids some aspects of the organic chemistry of derivatives of 3 146 Photochemistry and light absorption 4,236 Photography cyanine dyes in 4 327 Photo-oxidation primary processes in 14 146 464 QUARTERLY REVIEWS Photopolymerisation 4 236 Photosynthesis physicochemical aspects of some recent work on 14 1 74 Pinacol rearrangement 14 357 Polarity of the carbon-hydrogen bond 2 383 Polarography of organic compounds 6,262 Polonium chemistry of 11 30 Polyhalides and interhalogen com- pounds 4 115 Polymerisation initiation of by redox catalysts 9 287 Polymerisation of aldehydes 6 141 Polymerisation addition some thermodynamic and kinetic aspects of 12 61 Polymerisation induced by light 4 236 Polymerisation ionic 8 88 Polymerisation radical rate constants in 4 292 Polymers based on silicon chemistry of 2 25 Polymers high thermodynamic pro- perties of and their molecular interpretation 1 265 Polysaccharides enzymic degradation of 9 73 Polysaccharides enzymic synthesis of Portland cement constitution of 3 82 Process primary in photo-oxidation Proteins structural investigation of 6 Pteridines 6 197 Purines some aspects of the chemistry Pyrans some aspects of the chemistry Pyrimidines some aspects of the Pyrrole pigments biogenetic origin of 7 58 14 146 340 of 3 181 of 4 195 chemistry of 3 181 4 45 Quadrupole coupling nuclear and chemical bonding 11 162 Quadrupole moments molecular 13 183 Quenching of fluorescence 1 1 Quinones relation between the oxida- tion-reduction potential and chem- ical structures of 4 94 Radiations ionising action of on organic compounds 9,3 1 1 Radicals free electron resonance spectroscopy of 12 250 Radicals free interaction of with saturated aliphatic compounds 14 336 Radicals free mass spectrometry of 13 215 Radioactivation analysis 10 83 Radioactivity determination of geo- logical age by 7 1 Radioactivity of the heavy elements 5 270 Reactions unimolecular Arrhenius factors (frequency factors) in 14 133 Rearrangements aromatic 6 34 Rearrangements benzilic acid and related 14 221 Rearrangement pinacol 14 357 Redox potentials of quinone relation of to chemical structure 4 94 Reduction by metal-amine solutions ; applications in synthesis and deter- mination of structure 12 17 Reduction by metal-ammonia solu- tions of organic compounds 4 69 Relaxation processes molecular in liquids ultrasonic analysis of 11 134 Salt hydrates crystal structures of 8 380 Salts deposits of from oceans 1 91 Salts basic structure of 1,247 Salts solid ionic conductance in 6 Sandmeyer reactions 6 358 Semiconductivity and catalysis 11 Sesquiterpenoids recent advances in Shock waves 14,46 Silicon chemistry of polymers con- Silyl compounds 10 208 Sodium “flame” reactions 5 44 Solids molecular-sieve action of 3 Solids thermal transformations in 11 Solids transitions in 3 65 Solids separated by a narrow gap direct measurement of molecular attraction between 10 295 23 8 227 chemistry of 11 189 taining 2 25 293 246 CUMULATIVE INDEX 465 Solution aqueous thermodynamics of ion association in 14,402 Solutions aqueous mechanism of electrode processes in 3 95 Solutions of non-electrolytes theories of 13 306 Solvation ionic 3 173 Solvent extraction and its applications to inorganic analysis 5 200 Solvents ionising non-aqueous reac- tions in 10 451 Specificity in catalysis by metals 8 404 Spectra charge-transfer and related phenomena 8,422 Spectra emission of flames 4 1 Spectra far ultraviolet ionisation potentials and their significance in chemistry 2 73 Spectra infrared and Raman of hydrocarbons.Part I acetylenes and olefins 6 1. Part 11 paraffins 7 19 Spectra infrared of heteroaromatic compounds 13 353 Spectra Raman of inorganic com- pounds 10 185 Spectra rotation 4 131 Spectroscopy electron resonance of free radicals 12 250 Spectroscopy kinetic and flash photo- lysis 10 149 Stabilities of complex compounds 5 1 Stereochemistry of inorganic com- pounds 11,339 Stereochemistry of cyclohexane 7 221 Stereochemistry of elements of Sub- group VIB of the Periodic Table 10 407 Stereochemistry of elements of Group VIII of the Periodic Table 3 321 Steric hindrance 2 107; 11 1 Steroidal alkaloids 7,23 1 Structure of liquids in relation to their transport properties 14 236 Substitutions aromatic nucleophilic mechanism and reactivity in 12 1 Sugar epoxides 13 30 Sulphur nitride and its derivatives 10 437 Sulphuric acid behaviour of organic compounds in 8,40 Surface compounds the chemistry of Sydnones 11 15 carbon-oxygen 13 287 Tautomerism of phenols 10 27 Tetronic acids 14 292 Thermodynamics of ion association in aqueous solution 14 402 Thermochemistry of the elements of Group IVB and IV comments on 7 103 Thermodynamic properties estima- tion of for organic compounds and chemical reactions 9 229 Thermodynamic properties of high polymers and their molecular inter- pretation 1 265 Tracers radioactive preparation of 2 93 Transformation asymmetric and asymmetric induction 1 299 Transformations thermal in solids 11,246 Transition-metal compounds crystal- line electron resistance in 14 427 Transitions in solids and liquids 3 65 Transport control in heterogeneous reactions 6 157 Transport properties of liquids in relation to their structure 14 236 Triplet state 12 205 Triterpenes tetracyclic 9 328 Tropolones 5 99 .. Tryptophan biological degradation of 5 227 Ultrasonic analysis of molecular relaxation processes in liquids 11 134 Ultrasonic waves effects of on electrolytes and electrolytic pro- cesses 7 84 Veratrum alkaloids 12 34 Wool wax constitution of 5 390 X-Ray crystal analysis modern methods of determination of mole- cular structure by and their ac- curacy 7,335 p-Xylylene chemistry of and of its analogues and polymers 12 301

ISSN:0009-2681    

DOI:10.1039/QR9601400455

出版商:RSC    

年代:1960

数据来源: RSC