摘要:

QUARTERLY REVIEWS Printed in Great Britain by Butler & Tanner Ltd. Frome and London QUARTERLY REVIEWS Committee of Publication Chairman SIR CYRIL HINSHELWOOD M.A. Sc.D. D.Sc. F.R.S. SIR WALLACE AKERS C.B.E. B.R. W. BAKER MA. D.Sc. F.R.S. R. P. RELL M.A. B.Sc. F.R.S. G. M. BENNETT C.B. M.A. Sc.D. F. BERGEL D.Phil.Nat,. Ph.D. H. BURTON Ph.D. D.Sc. F.R.I.C. A. H. COOK Ph.D. D.Sc. D.I.C. F. S. DAINTON M.A. Ph.D. C. W. DAVIES D.Sc. F.R.I.C. M. G. EVANS D.Sc. F.R.S. C. S. GIBSON O.B.E. M.A. Sc.D. D. LL. HAMMICE M.A. D.Sc. SIR IAN HEILBRON D.S.O. D.Sc. D. H. HEY Ph.D. D.Sc. F.R.I.C. A. KING C.B.E. D.Sc. A.R.C.S. F. E. KING M.A. D.Sc. Ph.D. G. A. R. KON M.A. D.Sc. F.R.S. R. P. LINSTEAD C.B.E. M.A. Ph.D. F.R.I.C. F.R.I.C. F.R.S. F.R.I.C. D.Sc. F.R.I.C. F.R.I.C. F.R.S. LL.D.F.R.S. D.Phil. D.Sc. F.R.S. H. W. MELVILLE Ph.D. D.Sc. R. G. W. NORRISH B.A. Sc.D. S. PEAT Ph.D. D.Sc. F.R.S. S. G. P. PLANT D.Phil. M.A. B.Sc. E. K. RIDEAL M.B.E. M.A. D.Sc. J. M. ROBERTSON M.A. D.Sc. F. L. ROSE O.B.E. B.Sc. Ph.D. H. N. RYDON D.Sc. Ph.D. D.Phil. F.R.S. F.R.S. Ph.D. F.R.S. Ph.D. F.R.S. F.R.I.C. F.R.I.C. A.R.C.S. F.R.I.C. B. C. SAUNDERS M.A. Ph.D. D.Sc. F.R.I.C. D. W. G. STYLE Ph.D. S. SUODEN D.Sc. F.R.S. F.R.I.C. A. R. TODD M.A. D.PhiI. D.Sc. W. WARDLAW C.B.E. D.Sc. T. S. WEEELER Ph.D. D.Sc. F.R.S. F.R.I.C. F.R.I.C. M.1.Chem.E. F. G. YOUNG D.Sc. Ph.D. F.R.S. F.R.I.C. Editor R. S. CAHN M.A. D.Phil.Nat. F.R.I.C. Assistant Editors A. D. MITCHELL D.Sc. F.R.I.C. L. C. CROSS Ph.D. A.R.C.S. F.R.I.C. Indexer MARGARET LE PLA B.Sc. LONDON THE CHEMICAL SOCIETY CONTENTS KINETICS OF OLEFIN OXIDATION.By J. L. BOLLAND . LABORATORY AND TECHNICAL PRODUCTION OF FLUORINE AND THE CHEMISTRY OF THE DITERPENOIDS. By D. H. R. BARTON TRANSITIONS IN SOLIDS AND LIQUIDS. By L. A. K. STAVELEY THE CONSTITUTION OF PORTLAND CEMENT. By F. M. LEA . THE MECHANISM OF ELECTRODE PROCESSES IN AQUEOUS SOLU- ITS COMPOUNDS. By H. R. LEECH . TIONS. By A. HICKLING . COMPOUNDS. SOME ASPECTS OF THE ORGANIC CHEMISTRY OF DERIVATIVES OF PHOSPHORUS OXYACIDS. By F. R. ATHERTON . RILEY . KINETICS OF THERMAL i'4DDITIOl.r O F HALOGENS TO OLEFINIC By P. B. D. DE LA MARE. CARBIDES NITRIDES AND CSRBONITRIDES OF IRON. By H. L. IONIC SOLVATION. By J. O'M. BOCKRIS . SOME ASPECTS OF PYRIMIDINE AND PURINE CHEMISTRY. By MECHANISMS OF HYDROGEN CATALYSIS. By D. D. ELEY . HYPERCONJUGATION. By V. A. CRAWFORD . NATURALLY OCCURRING PEPTIDES. THE TERRESTRIAL DISTRIBUTION OF THE ELEMENTS. MOLECULAR-SIEVE ACTION OF SOLIDS. By R. M. BARRER . RECENT STEREOCHEMISTRY OF THE GROUP VIII ELEMENTS. THE CONDENSED PHOSPHATES. By B. TOPLEY . CARBOHYDRATE SULPHATES. By E. G. V. PERCIVAL . B. LYTHGOE . By R. L. M. SYNGE By DAVID T. GIBSON . By R. S. NYHOLM . PAQE 1 22 36 65 82 95 126 146 160 173 181 209 226 245 263 293 321 345 369

ISSN:0009-2681    

DOI:10.1039/QR94903FP001

出版商:RSC    

年代:1949

数据来源: RSC

摘要:

LABORATORY AND TECHNICAL PRODUCTION OF FLUORWE AND ITS COMPOUNDS By H. R. LEECH M.Sc. F.R.I.C. (RESEARCH DEPT. IMPERIAL CHEMICAL INDUSTRIES LTD. GENERAL CHEMICALS DIVISION WIDNES.) " IN my opinion the hazards of work with fluorine and its compounds have been greatly over-rated. When treated with the respect which is due to it fluorine is just another substance." 1 Fluorine was made on an industrial scale in the U.S.A. in the last war in simple equipment largely of mild steel and handled without difficulty. A large fluorine plant was operated in Germany also. Fluorine can now be made in the laboratory or in industry without difficulty and the chemistry of fluorine can begin to overtake that of other common elements which have been readily available for many years. It is of interest to see the stages of the development of fluorine production the problems which have been solved and those which yet remain.Although it is 62 years since Moissan first isolated fluorine in 1886 there was little further work done for 30 years and developments alillost as revolutionary as Moissan's first preparation may be dated €rom 1913 when Mat>hers and his co-workers first used as electrolyte fused potassium acid fluoride. Between 1886 and 1919 there were only some six papers published by workers in the field of elernenta.ry fluorine between 1919 and 1939 there were a t least 25 papers giving some description of fluorine cells as well as 9 patents and many more papers dealing with the use of elementary fluorine. All fluorine cells employ a potassium fluoride-hydrogen fluoride electro- lyte there are several compounds formed in this system and Cady3 gives the data of Table I (the tension of hydrogen fluoride is the approximate partial pressure at the melting point).Electrolytes in three different working regions have been employed (1) Low-temperature electrolyte a relatively dilute solution of potassium 64.3" 61.8 71.7 68.3 239.0 229.5 fluoride (about KF,13HF -55 -20 -15 -26 -15 - with less than 20y0 by weight of potassium TABLE I Solid phase. HF Eutectic . KF,4HF . Entectic . KF,3HF . Eutectic . nil 17.7 42.1 36.3 49.2 52.1 M.p. - 83.7" - 97 72.0 63.6 65.8 62-4 HF tension Inm. -250 -130 - Solid phase. XIF,2*5HF Eutectic . KF',BHF . Eutectic . KF,HF . Eutoctic . KF "/b 53.8 65.8 59.2 61.5 74.4 75.4 HI? tension nm. 1cz.p. 1 G. H. Cady I d . Eng. Chem. 1947 39 No.3 1OA. 2 W. L. Ago F. C. Mathers B. Humiston and C. 0. Anderson Trans. Electrochem. SOC. 1919 35 335. J . Amer. Chern. Soc. 1934 56 1431. 22 LEECH PRODUCTION OF FLUORINE 23 fluoride) as used by Moissan at subnormal temperatures. (2) High- temperature electrolyte approximately molten KF,HF first introduced by Mathers working temperature about 250". (3) Medium-temperature elec- trolyte approximately molten KPJHF first introduced in 1925 by P. Lebeau and A. Damiens ; 4 working temperature about 100". The partial pressure of hydrogen fluoride over the low-temperature electrolyte is very high and the fluorine produced is heavily contaminated. Over the other two electro- lytes the partial pressure is very much less and the fluorine (and hydrogen) are contaminated with 5-15o/d of hydrogen fluoride a t the working tem- perature.have investigated the possi- bility of finding an electrolyte with lower melting point and draw attention to the advantages of czsium acid fluorides owing to the low melting points the hydrogen fluoride tension of these is negligible. Some attention to this point has also been paid by German workers. In the low-temperature electrolyte the corrosion of the platinum anodes which must be employed is very heavy. indicates a current efficiency of 31% on fluorine and a platinum loss of 5 g. per g. of fluorine (although as recently as 1932 proposals were made for a somewhat modified cell working a t room temperature claiming advantages in a nickel anode).' Moissan found that graphite anodes completely disintegrated almost immedi- ately on starting electrolysis in low-temperature electrolyte and found that platinum in high-temperature electrolyte was too rapidly corroded to be of any value.He did not examine graphite in this electrolyte however and it was left to Argo Mathers Humiston and Anderson to show how effective this was and to open the door to a new development in fluorine production. Medium-temperature electrolyte using a nickel anode was proposed by Lebeau and Damiens for the specific reason that the formation of carbon fluorides reputed to occur in the high-temperature cell was avoided and a purer fluorine obtained. This electrolyte had other advnnhages however and will probably oust all others from genera'l use with in addition an amorphous carbon anode which later work has shown to be possible. Of the work with low-temperature electrolyte there is little more to be said.Moissan showed that copper is inert and anodically passive to fluorine and Soci&t& Poulenc Freres et M. Meslans patented a cell in which the platinum anode was attached to a copper cylinder located centrally in a cylindrical cell and surrounded by a perforated copper diaphragm which did not need to be electrically insulated from the anode. Thus they avoided the difficulty of sealing the anode into the anode compartment in a manner which would retain its insulation value and resistance to fluorine. This cell arrangement proposed as the basis for a manufacturing plant instal- lation has a very modern appearance and was exhibited a t the Exposition Universelle de Paris in 1900. F. C. Mathers and B. T. Stroup 0.Ruff Compt. rend. 1928 181 917 ; P. Lebeau Bull. SOC. d'Encourag. 1927 139 15. Trans. Electrochem. SOC. 1934 66 245. " Die Chemie des Fluors " Verlag Springer Berlin 1920. ' W. S. Calcott and A. F. Benning U.S.P. 2,034,458 (1936). G.P. 129,825 (1902). 24 QUARTERLY REVIEWS The early workers in this field laboured under more difficulties than the choice of electrolyte and anode. The raw material for their work was aqueous hydrofluoric acid from which potassium acid fluoride was made and crystallised dehydrated and then decomposed by heating to give the anhydroua acid. It was obviously an advantage of the high-temperature electrolyte that one stage of this preparation could be omitted and then in the 'twenties supplies of the acid fluoride could be purchased and the chemical side of the problem of making fluorine became much simpler.In the 'thirties supplies of anhydrous hydrogen fluoride also became available and the medium-temperature cell with the possibility of electrolyte revivification from this source was a t no disadvantage. Fluorine Cell Development from 1919 to 1939.-The studies on fluorine production by MatJhers and his co-workers were required by the Chemical Warfare Service of the U.S. Government. A cell similar in form to that of Poulenc and Meslans was developed. The heavy copper cont,aining vessel 8 ins. deep 3-5 ins. diameter served as cathode and was externally electrically heated. The sheet-copper diaphragm 2 in. in diameter was slotted a t the lower end and closed a t the bottom. Inside the diaphragm was an Acheson graphite anode suspended from a copper rod which was insulated from the diaphra'gni by rz gland packed with powdered fluorspar rammed hard.It was bettler to insulate the diaphragm for some corrosion occurred when it was anodic. In starting a cell only a low current could be passed. If too high a current density were applied the cell quickly polarised the current fell and a potential of 50-60 volts was required to maintain the original current density. In these circumstances there was the appearance of a gas film round the anode with small sparks through it (this is very similar to the well-known " anode effect " of fusion electro- lysis). This effect was attributed to the presence of small amounts of water in the salt and the formation of an oxygen film owing to its prior discharge. The phenomenon is constantly referred to by later workers.There is no explanation of how the oxygen discharge gives rise to the " gas film " and as will be seen later there is a very interesting field of study,still almost untouched in the phenomena a t fluorine-carbon anodes especially in presence of small quantities of water. Mathers electrolysed a t a current density of 0.1-0-2 amp./sq. in. for several hours. During this period fluorine was not evolved but when i t began to appear the current density could be increased to the normal working figure of 0-5-1.0 amp./sq. in. At 250" t4he cell took 10 amps. a t 15 volts. Some corrosion of the copper parts occurred and copper fluoride thickened the melt a process assisted by the deposition of potassium fluoride as the hydrogen fluoride content decreased.To some extent this process could be avoided by steadily increasing the temperature of elecfro- lysis but this on the other hand increased the rate of corrosion of the copper and the volatiliEation of hydrogen fluoride and above 300° attack on the graphite anode became considerable. As the electrolyte became thicker there was a tendency to frothing and this led to electrolyte being carried into the outlet pipe and then solidifying. The fluorine was then LEECH PRODUCTION OF FLUORINE 25 forced under the diaphragm mixed with the hydrogen and caused explosions. It was not found possible to regenerate the electrolyte by passing ia hydrogen fluoride and therefore when the melting point of the electrolyte was up to about 2S0° it was discarded and a fresh batch introduced.Mathers com- mented that it was remarkable that in the years he was working with fluorine Ruff did not discover this relatively simple method and considered that there were no special difficulties in the manipulation of the apparatus. The problems indicated-sealing in the anode polarisation corrosion of the container outlet-pipe blockage-are the main subjects of attention by subsequent workers. Many cells of a very similar sort of size and capacity were introduced in the next twenty years. in 1921 took up a suggestion of Mnthers and used as container artificial graphite. They had a special ribbed and club-shaped anode to reduce current density and pre-electrolysed at a low current density. They investigated the effect of other fluorides in lowering the melting point of thc electrolyte but found the partial pressurc of hydrogen fluoride was increased by any addition.There T i m some ozone in the anode gas in the early stages but never more than 0.27; G f carbon fluorides. A cell of the Mathers pattern was used by W. R. SmythelO for study of the spectrum of fluorine. The hydrogen fluoride was removed by sodium fluoride and the fluorine then had very little action on glass. J. Simons l1 in 1924 described a cell very similar to that of Mathers he found Portland cement rna'de a n adequate anode seal and the electrolyte was pre-electrolysed a t low current dcnsity in an open cell until fluorine was evolved. Many workers used a cell of the Simons pattern in the next 15 years in some cases monel metal being used in place of copper. S. I?. Whearty junr.,12 used a cast magnesium body and an electrolyte containing 35% of sodium fluoride and working a t 170".M. Bodenstein H. Joliusch and H. Krekeler l3 also used a magnesium alloy cell body but introduced the electrodes from below the sealing in of the electrodes by solidified electrolyte was the subject of a patent assigned to I.G. Farbenindustrie.l4 A return to Moissan's cell type was shown by L. M. Dennis J. M. Veeder and E. G. Rochow,15 who describe a V-shaped cell made of copper pipe and several workers used this arrangement in copper or in nickel. In 1925 Lebeau and Damiens introduced a cell using medium-temperature electrolyte with a metal preferably a nickel anode. This was later to become the leading type. Several workers used this electrolyte and its use by Cady l6 is noteworthy because it was the first case in which anhydrous hydrogen fluoride was obtained from a manufacturer and used for regenera- tion of the electrolyte in situ.F. Meyer and W. Sandow Current efficiency was 750/,. This was in 1935. Rer. 1921 54 759. l1 J . Amer. Chem. SOC. 1924 46 2175. l3 Chem. Pabr. 1936 8 283. l4 H. Krekclcr G.P. 522,885 (1931) ; 558,829 (1932). l5 J . Anaer. Chem. SOC. 1931 53 3263 ; L. M. Dennis and E. G. Rochow ibid. lo Astrophys. J. 1921 54 133. 12 J . Physical Chem. 1931 35 3121. 1934 50 879. l6 Ibid. 1935 57 246. 26 QUARTERLY REVIEWS An important study of factors affecting carbon anode behaviour was made by K. Fredenha'gen and 0. Krefft.17 They dried their potassium bifluoride in a stream of dry air a t an elevated temperature and tested for dryness by distilling off some hydrogen fluoride which had to have a specific conductivity a t 0" of less than 0.02 mho.I n an electrolyte so prepared a practically pure fluorine could be generated immediately a t a graphite or amorphous carbon anode and a reproducible current-voltage curve could be obtained. If water were added polarisation occurred and no reproducible curve could be obtained until the water content exceeded 1% but then the anode gas was oxygen. It was found also that for electrolytes with HF KF ratio below 1.8 graphite was unwetted and could then be used satisfactorily as an anode. Above this ratio (38.3% HF) wetting occurred and caused disintegration of the anode. Amorphous carbon anodes behaved similarly but the limit at which wetting began was different-actually a t a much higher hydrogen fluoride content.The use of anodes of graphite or carbon in an electrolyte which did not wet them was the basis of a patent claim by Fredenhagen.l* Eater papers by A. L. Henne19 and Cady D. A. Rogers and C. A. Carlscjn 2O were not so clear as to when a graphite or carbon modo could be employed in medium- temperature electrolyte. American Wartime Developments.-During the second world war fluorine production was developed in U.S.A. in connecfion with the atom bomb in Germany in connection with a wartime requirement for chlorine tri- fluoride. It is surprising that although the principal interest in America before the war had been in high-temperature cells yet the industrial develop- ments were in medium-temperature cells first with nickel anodes later with carbon anodes ; 21 and whilst it was German work which had prin- cipally pointed the way to the possibilities of the medium-temperature cell wartimo expansion there was of the high- temperature cell.22 I n the American developments cells of 1000-2000-amp. capacity with medium- temperature electrolyte were developed by Hooker Electrochemical Co. Harshaw Chemical Co. and E. I. du Pont de Nemours & Co. A large semi-technical installation of 600-amp. cells of high-temperature type is also described by Fowler et al. and smaller installations by Miller and &Bee of medium-temperature cells. A detailed account of the du Pont cell will be given as representative the work on this especially in con- nection with nickel anodes has been described in considerable detail by R. C. Downing.23 The original choice of the medium-temperature electrolyte using nickel anodes might be questioned but comparing the position as now known when carbon anodes have successfully replaced nickel there can be 2.Elektrochenz. 1929 35 670. G.P. 493,873 (1930) ; 511,808 (1930). l9 J . Amer. Chem. SOC. 1938 60 96. 21 For a full account of American wartime developments see various papers ibid. 1947 34 (March). 2 2 German work in the fluorine field is fully described in B.I.O.S. 1595 ; see also H. R. Neurnark Trans. Electrochem. SOC. 1946 91 proprint 3 ; and B.I.O.S. 72 ; 261 ; C.I.O.S. XXII-17; 22/XXIX-l4; F.I.A.T. 838; P.B. 6641. aa P.B. 60796. 2o I n d . Eng. Chem. 1942 34 443. LEECH ; PRODUCTION OF FLUORSNE 27 little doubt that this gives the most economical arrangement. The corrosion is very much less than in high-temperature electrolyte mild steel may be employed for cell construction the control of a temperature of about 100" is much simpler than one about 250" and the anodic polarisation tendency is less pronounced.Fluorine manufacture was started with large numbers of nickel anode cells but the current efficiency was low about 70% the nickel consumption heavy and electrolyte conditioning to remove nickel fluorides was a very big job. Downing states that the sludge contains NiP,,KF. A fluoride of tervalent nickel has not been previously reported. The cells were all finally converted to carbon anodes. The cells had a rectangular steel container about 4 ft. long 2 ft. deep 13 ft. wide provided with a jacket for circulating w-ater to maintain optimum temperature con- ditions.The steel cover carried electrodes and diaphragms in rows along the length. There were two rows of anodes built up each of six carbon plates side by side. Each plate was 18 ins. long 6:; ins. wide 1; ins. thick. To each row of anodes there was a double row of sheet-steel cathodes and between the facing electrodes was a diaphragm solid metal in the gas space perforated monel metal sheet .in the electrolyte. The anodes were bolted to copper carriers and these supported by copper rods which passed through stuffing boxes in the cover. The stuffing box was made gm-tight and electrical insulation provided by rings of '' Teflon " the solid polymer of tetrafluoroethylene which was itself a wartime discovery. 24 This is a hard horny material inert to all reagents including even fluorine under ordinary conditions electrically non-conducting and solid up to a t least 300" The cathode was similarly supported and insulated.The cover was provided with gas-outlet connections and a pipe for hydrogen fluoride addition provided. This cell took about 1600 amps. a t a voltage of 5.5 a t the start gradually deteriorating to 11.0. The working temperature was in the range 95-115" the current density was 0.5 anip./sq. in. the -current efficiency more than 9On/, the anode gas contained 5-15% of hydrogen fluoride and on a hydrogen fluoride-free basis the fluorine content was greater than 95% with a trace of fluorine oxide F,O. If it had not been found possible to use carbon anodes the very hoavy consuniption of nickel and expensive electrolyte regeneration operations would probably have made the high-temperature cell with a graphite anode more economic.The work of Predenhagen and Krefft had indicated clearly the controlling factors although they had suggested a composition between KF,HF and KF,l.GHF when graphite could be employed and a temperature a t the start of 160". With this camposition a t this tem- perature the hydrogen fluoride vapour pressure is high and the generally favourable conditions (low corrosion ease of control) associated with a lower temperature and higher HP proportion (up to KF,2*2HF) are begin- ning to disappear. In this most favourable range it was never found possible to employ graphite but amorphous carbon was satisfactorily used. 24 E. B. Yelton Chem. Eng. 1947 54 No. 3 264; Chem. Met. Eng. 1946 53 No. 4 145. 28 QUARTERLY REVIEWS The cells still showed a tendency to polarisation which has several possible origins as follows.(I) The electrical contact to the anode could deteriorate and indeed it has been suggested that the provision of a permanently satisfactory connection is one of the remaining outstanding problems. The gradual increase of the voltage from 8.5 a t the start to 11.0 or more was largely caused by this deterioration. Each cell W ~ S provided with a subsidiary nickel anode which carried all the current a t the start and the anode gas was mainly oxygen. When the anode gas had reached a certain fluorine content the carbon anodes were switched in. Accumulation of water (from the make-up hydrogen fluoride) might occur and some use of the nickel anode might be necessary again during the course of operation.Downing says that there was some other un- explained effect of this electrolysis at a nickel anode in addition to its effect in removing water. (3) Low hydrogen fluoride concentration could sometimes cause polarisa- tion. It is suggested that 37.5% of hydrogen fluoride equivalent to KF,1.75HF was a limiting figure and that in this case the voltage rise occurred a t the cathode. Normally the bulk of the voltage drop occurs a t the anode. This difficulty was immediately cured by addition of acid the preferred range of acid content being 38-40%. (4) Polarisation could still occur not attributable to any of the above effects it was called " gas film " polarisation and attributed to non- wetting of the carbon anodes by the electrolyte. Pinkston states that the anodes were not wetted by the electrolyte and when removed from the liquid they wore clean and black.This is a repetition of the observation by Cady,20 who further stated that such anodes were not wetted by tap water but carbon cathodes in the same electrolyte did not become non- wetting. It was found that this difficulty was minimised by the addition of 1-2y0 of lithium fluoride to the electrolyte; this addition was made in the first place in an attempt to lower $he melting point of the electrolyte and the Harshaw workers observed this other effect of the addition. Schumb on the other hand states that the lithium fluoride was insoluble and tended to settle out but if the mud a t the bottom of the cell was stirred up there was a temporary improvement of the cell performance as regards polarisa- tion tendency.Aluminium fluoride had a similar effect and equally tended to settle out. The addition of 142% of lithium fluoride became standard practice in the American industrial installations and has been the subject of a ~ a t e n t . ~ 5 Downing states that the two discoveries which eliminated polarisation as an obstacle to the commercial operation of carbon anode cells were the addition of lithium fluoride to the electrolyte and the conditioning of the electrolyte by operating with a nickel anode. The carbon anodes used in these cells were of a special character. The du Pont cell had a carbon especially strengthened by impregnation with carbonaceous material and z 5 W. C. Schumb and A. J. Stevens U.S.P. 2,422,590 (1943). (2) Water in the electrolyte exerted its known effect.LEECH PRODUCTION OF FLUORME 29 rebaking and the Harshaw cell had a carbon rod impregnated with copper the latter was stronger permitted better electrical connection being made and was not so sensitive to acid concentration. It may be said that all this American work solved very satisfactorily the problem of making fluorine on a large scale but left unsolved the interesting theoretical problem of the behaviour of carbon anodes. In low-temperature electrolyte graphite almost immediately on being rendered anodic swells and disintegrates a behaviour which persists until the electro- lyte composition reaches that of medium-temperature electrolyte ; even then polarisation iec so severe as to render graphite unusable. Graphite anodes may be employed in high-temperature electrolyte but even then there is a gradual deterioration.Amorphous carbon completely polarised if not disintegrated in low-temperature electrolyte may be satisfactorily employed (but with some limitations) in medium- and in high-temperature electrolyte. Precisely what is the relation to these phenomena of the behaviour attributed to water in the electrolyte and its own intense polarising influence is un- explained. Would polarisation (and disintegration ?) disappear if rigidly water-free systems were employed ? How does oxygen evolution cause such intense polarisation ? A further unusual phenomenon is the method of evolution of the fluorine itself which A. J. nudge W. N. Howell and H. Hill 26 have related to the high angle of wetting a t the anode but which requires further study and which may cast an interesting light on the puzzling “ anode effect ” observed in fusion electrolyses.An interesting feature of the Pennsylvania Salt Mfg. Co.’s cell described by J. F. Gall and H. C. Miller 27 and by R. W. Porter 28 was that no dia- phragm was interposed between tho electrodes only a gas barrier immersed to a depth of 2 in. to divide anode from cathode gas. The high-temperature cell described by E’owler seems a very practical equipment but requires monel construction instead of steel and corrosion was appreciable in places polarisation skems to have been a recurrent phenomenon and the graphite anodes had a restricted life. Regeneration of the electrolyte with hydrogen fluoride vapour was possible and the cell worked a t an anodic current density of 300 amps.per sq. ft.-four times that of medium-temperature cells-so that a more compact installation was possible. German Wartime Devellspments.-Two German cells developed during the war are worthy of attention. I.G. Farbenindustrie developed for experimental purposes only a cell of medium-temperature type at their research laboratories a t Leverkusen. They had developed a 250-amp. cell by 1940 and a 2000-amp. cell by 1942. The construction was in magnesium alloy with hard-carbon anodes impregnated and re-baked and magnesium sheet cathodes. There was no diaphragm only a gas-separating barrier. The 2000-amp. cell was long and narrow (10 ft. long 1-6 ft. wide and deep) and had external electrolyte circulation and cooling. The electrolyte con- tained about 46% of hydrogen fluoride (KFY2.5HP) the working temperature was 75-85” and in these conditions even when hydrogen fluoride containing 2* Nature 1947 160 604.27 Ind. Eng. Chem. 1947 39 262. Chem. Eng. 1948 55 No. 4 102. 30 QUARTERLY REVIEWS 2-3% of water was used for make-up no trouble was experienced with polarisation. A fluorine plant was erected a t Falkenhagen near Berlin to make 720 tons per annum of fluorine for conversion into chlorine trifluoride. This plant using high-temperature electrolyte was apparently under the direct control of the German High Command. There had obviously been a good deal of study of fluorine production on which the design of the cell was based but it is not known what the antecedents of this plant were. It is indeed noteworthy that the I.G. cell was not developed on a manu- facturing scale for this plant.The O.K.H. cell (Ober Kommando des Heeres) had a capacity of 2000-2500 amps. and was made in magnesium alloy with graphite anodes and silver cathodes ; each electrode was sealed into a diaphragm bell of magnesium alloy slotted in the area where the electrodes were facing each other. Each cell stood on its own weighing machine to control the hydrogen fluoride input and was provided with its own rectifier for D.C. supply. Grezt stress was laid on the purity of the electrolyte and of the make-up hydrogen fluoride ; water and sulphur oxides must be completely removed but some hydrofluorosilicic acid (up to 3% in the electrolyte) was permissible. The electrolyte was purified by pre-electrolysis before being charged into the cell whieh had then to be operated for an hour a t 30-60 volts t o condition the anodes before it was installed in its normal working position.The acid for cell make-up was piirificd by passage with 1-274 of fluorine through a nickel reactor at 300". This acid after condensation was re-vaporised for addition to the cell the addition being controlled by the weight of the cell and a catharometric record of the hydrogen fluoride in the cathodic hydrogen. The cell operated between 2-15" and 253" the starting voltage was 6.0-6-5 which gradnalIy rose over r2 period of 3 months to 11.6 a heavy load of up to 5800 amps. was then app!ied for 5-10 minutes when normal operation wm recommenced the voltage retwning to the initial figure. The anodic current density mas GO-7Q amps. per sq. ft. which n'as very similar to American medium-temperature pracficc and very different from the very high values a t which Fowler's cell ran.A current efficiency greater than 90% was obtained. Some cmrosion of the silver cathode and the magnesium parts occurred so that af+er a year or so the electrolyte was emptied from the cell to remove accumulated sludge. The total li€e of the anode is stated to have been 12 months but the reason for the termination of anode life is not given. A good deal of interesting work appears to have been done in connection with this cell development and some of it has been reported by Neuinark. The absorption of fluorine on graphite and the formation of complex inter- calation compounds is described and i t is suggested that this accounts for the gradual deterioration of the cell voltage. The fluorides of rubidium and caium were also studied as possible alternatives to potassium and the conclusion reached that no advantage was to be observed.Kwnsnik on the other hand states that they would be preferred in the I.G. cell were it not for their high price and scarcity. This seems to require further examination. LEECH PRODUCTION O F FLUORINE 31 Chemical Production of Fluorine.-Perhaps a word should be said with regard to the attempted chemical production of fluorine. This was of course studied from Davy onwards and he was well aware of the difficulty he would have in finding vessels which would withstand fluorine a t the high temperatures presumably necessary. Platinum and gold are not particularly good in this connection. Brnuner was reported to have been successful in making fluorine in 1882 by thermal decomposition of the tetrafluorides of lead and cerium but in 1916 0.Ruff 29 cast doubt on this and B. Brauner 30 agreed with him. The studies which produced the Mathers cell also embraced chemical preparations and G. L. Clark 31 describes methods of preparing complex salts such as 3KE',HF,PbP and Na,PbF the former loses hydrogen fluoride a t 250" and evolves fluorine at 300° and the latter may decompose a8t 250". The studies of M. Jellinek and A. Rudat 32 on the reducibility of fluorides by hydrogen are interesting and show very high heats of formation e.g. for FeF,. A patent for the production of fluorine by action of oxygen on the oxyfluorides of titanium zirconium or hafnium was taken out in 1926.33 The difluoride of silver AgP, was first reported by M.8. Ebert E. 1,. Rodowskas and J. C. W. Frazor in 1933,34 and it is suggested,35 without confirmation that thc equilibrium pressure of fluorine over this salt reaches 1 atmosphere a t about 450". It is probable that with increasing knowledge of materials resistant to fluorine it would be possible to find a fluoride which would evolve fluorine on heating and this may be a mettiis of generat- ing very pure fluorine. During the war very considcrable use was made in America of fluorine carriers espccially cobalt trifluoride for fluorinating hydrocarbons. In addition AgF, MnF, CeF, PbF, HgF, and others were studied. These higher fluorides were made by treatment of lower- valency compounds with electrolytically produced fluorinc aiid i t is probable that this method of applying fluorine ma'y undcrgo further development.Handling of Flnor~e.-Consiciernble confusion anrJ mi.;apprehcnsion have been prevalent with regard t o the dificulCies of wxking wit,h fluorine. It reacts fairly rcsdiiy with many organic m3,terials such as rubber aiid textiles and with moisture the hydrogen fluoride present in gaa direct from the cell reacts of course with glass ; but after romsval of this hydrogen fluoride fluorine can be handled readily in glass harder glasses being more resistan5 and silica excellent.36 Tlrus pure fluorine free from hydrogen fluoride out of contact with rubber is quite inert in glass or metal equipment. For connections especially in metal pressure or force joints as commonly used in domestic plumbing and used by Henne l9 for making connection to his cell are very useful.For stopcock lubricants Dry metals also are resistant. 29 2. anorg. Chem. 1916 98 27. a1 J . Amer. Chem. SOC. 1919 41 1477. s a 2. canorg. Chem. 1925 175 281. 33 N. V. Phillips Gloeilampenf~brikien B.P. 362,918 (1926). 3 p J . Amer. Chem. SOC. 1933 55 3056. 35 0. Ruff and M. Giese 2. anorg. Chem. 1934 219 143. 36 S . Aoyama and A. Kanda Bull. Chem. SOC. Japan 1937 12 409. Ibid. p. 38. 32 QUARTERLY RE VIEWS material of the fluorocarbon type is desirable and this a t present is not available commer cia11 y . For removing hydrogen fluoride the cooling possible with solid carbon dioxide is inadequate for the vapour pressure is still appreciable at -60". If cooling is to be resorted to liquid air must be used. A better method is the use of sodium or potassium fluoride as absorbents as first used by Moissan.The former is preferred as it does not give any liquid products which may cause blockages in the apparatus. These have been generally used by fluorine workers and the sodium fluoride is preferably used in a granular or pelleted form. Data on the effect of cooling and of sodium fluoride absorption in removing hydrogen fluoride have been given by the du Pont workers.21 Porter describes how sodium fluoride absorbers are regenerated in situ by heating. At the O.K.H. plant in Germany potassium fluoride was used and liquid products drained off. Even a t temperatures up to 100" at least mild steel copper nickel monel aluminium magnesium and brass are practically completely inert to fluorine and there is no need to use platinum. Atl higher temperatures platinum is not very good nickel or monel is best being useful even a t 600°.21 37 Soft metals lead and tin are not resistant and soldering cannot be used.Amongst non-metallic materials sintered alumina now becoming commercially available is resistant up to a t least 700°,38 and there is no need to go to the specially made fluorspar or fluoride porcelains described by Damiens 39 and by 0. Ruff and A. Riebeth.40 Fluorine compression is not very easy mechanically although it has been done up to 40 Ibs./sq. in.21 For higher pressures the gas is liquefied by cooling with liquid air or nitrogen and then allowed to evaporate under pressure into a suitable container. H. von Wartenberg 41 has referred to the use of a cylinder containing fluorine a t 2000 lbs./sq. in. supplied to him by I.G.Farbenindustrie before the war and I.G. practice has been described.22 Gas compressed to 400 lbs./sq. in. was apparently used in America during the war but only under stringent precautions. A trace of grease or other organic matter could react violently and cause such a local high temperature as to set the metal of the valve burning leakage through the packing of the gland could have the same effect. Containers of compressed fluorine were therefore stored behind heavy steel or thick brick walls and valves manipulated by remote control. In the light of this it seems improbable that compressed fluorine is ever likely to become an article of commerce. In the liquefaction and re-evaporation of fluorine Ruff and 0. Bret- schneider 42 pointed out that explosive compounds of an unknown char- acter possibly C1OF or 0, accumulate in the less volatile residues.Both I.G. Farbenindustrie and Penn. Salt follow Ruff's advice and heat the fluorine to 300° to decompose these impurities before liquefying it. W. R. Myers and W. B. delong Chem. E n g . Progress 1948 44 359. 3* 0. Hannebohn and W. Klemm 2. anorg. Chem. 1936 229 336. Compt. rend. 1931 192 1235 ; A. Damiens and L. Domange ibid. p. 1711. 4o 2. anorg. Chem. 1928 173 373. 4l Ibid. 1939 243 406 ; 1941 247 135. 4 a Ibid. 1934 217 1. LEECH PRODUCTION OF E'LUORTNE 33 Anhydrous Hydrogen Fluoride.-Moissan's procedure for making his anhydrous liquid has already been described. The thermal decomposition of acid potassium fluoride and the conditions required for production of acid of low moisture content have been studied by K.Fredenhagen and G. Cadenbach ; 43 and although on a small scale fluorine cell workers were content to purchase the acid fluoride and discard it when partly exhausted yet for large-scale manufacture a supply of anhydrous acid was essential for both medium-temperature and high-temperature cells. A demand for anhydrous hydrogen fluoride (" AHF ") in industry first developed about 1930 in the U.S.A for the manufacture of the chlorofluoro- methanes the "Freons ".44 About 10 years later a further demand developed also in the U.S.A. for the use of this acid as alkylation catalyst for producing aviation petrol in the petroleum industry. The American wartime fluorine industry thus found the plant in existence to supply its raw materials. Production of some 25,000 tons of AHF was estimated in 1944.I n Germany a special plant was built in Bavaria to supply the O.K.H. plant although I.G. also had an AHF plant at Leverkusen. The method of manufacture is by the action of concentrated sulphuric acid on fluorspar at a temperature of about 250". The fluorspar should be high grade may have been subjected to a flotation process to remove impurities should be low in silica galena and moisture and have a minimum of 98-99Yo CaF content. It is finely ground dried mixed with acid and fed into the reaction vessel. Penn. Salt in their plant a t Cornwell Heights use a rotary kiln externally gas fired and the acid is absorbed in weaker aqueous solution to give an 80% solution which is fractionally distilled to give an anhydrous acid and a weaker solution returned to the absorption system.The plant a t Stulln Bavaria with a capacity of 3000 tons of AHF per annum uses a stationary retort the acid-spar mixture being forced through by slow paddle agitators. The acid is con- densed by cooling t.0 give a product with 10% of water which is batch- distilled through fractionating columns to give a pure anhydroun acid. The I.G. plant with a capacity of 10,000 tons per annum used rotary kilns of steel plate brick-lined the acid is condensed by cooling and the crude product contains 5% of water but a purer product is obtainable by separately collecting the condensate from the final condenser in the series. Some Recent Developments in Fluorine Compounds.-Finally i t is of interest to draw attention to developments in the field of fluorine com- pounds more particularly those involving elementary fluorine in their production.Hence we will not refer further to developments in recent years of boron trifluoride and fluoroborates of the chlorofluoro-derivatives of methane and ethane such as CF,Cl, which have become known generally under their trade name of " Freons " or to the polymers of tetrafluoro- ethylene and chlorotrifluoroethylene. The most outstanding developments of recent years have been in the field of the fluorocarbons. Carbon tetrafluoride was very incorrectly 4 4 J. R. Callahan Chem. Met. Eng. 1945 52 94. Ibid. 1929 178 289. U 34 QUARTERLY REVIEWS described by Moissan 45 and only properly identified by Lebeau and Damiens in 1926.46 It is a gas liquefied a t atmospheric pressure a t - 128' stable and chemically inert unattacked by most reagents.Ruff and R. Keim 47 in 1930 and Ruff and Bretschneider in 1934 42 described a number of fluorocarbons formed by the action of fluorine on carbon up to C5FE2 and J. H. Simons and L. P. Block 48 went up to C7F14. These compounds analogues of the hydrocarbons are all stable and inert and above the butane derivatives actually have boiling points lower than the corresponding hydrocarbon. In addition a t temperatures below about 400° Ruff and Bretschneider showed that different forms of carbon give rise to a solid monofluoride (CF), apparently formed by intercalation of fluorine molecules betn-con the la'ycr planes of the graphite crystallites. It is a chemically inert compound which howcver decomposes a8bove 400" into carbon tetra- fluoride and higher fluorocarbons ; in presencc of fluorine particularly this decomposition occurs explosively.The American wartime fluorine cell developments were largely for the production of fluorocarbons. Two types of compound were required a volatile liquid and a lubricating material ; for the former perfluorodimethyl- cycbhexaiie C6Flo(CF,) was made for the latter various types of hydro- carbon or chlorohydrocarbon were fluorinated. A very wide range of fluoro-compounds was made both of aliphatic and polycyclic character mostly saturated. McBee 21 has described the production of perfluoro- benzene c6F6 but says very little regarding its properties. It is a liquid b.p. 81-82". The properties of these compounds have been described by Fowler and by Cady and Grosse.21 A variety of methods of preparation was employed.The direct fluorination of hydrocarbons with fluorine over a silver-copper catalyst is described by Cady but in general the process used a fluorine carrier of the type of cobalt trifluoride. In many cases hydrocarbon materials were chlorinated and the chlorine replaced with fluorine by treatment with hydrogen fluoride or other agent before com- pletion of the substitution and saturation in the above way. Sulphur hexafluoride was made in 1900 by Moissan and Lebeau by burning sulphur in fluorine and can still only be made by this or a related method. It has a very high electrical breakdown capacity and this com- bined with its low boiling point has made it particularly suitable for filling the Van de Graaff high-voltage generat0r.4~ The production of sulphur hexafluoride on a laboratory scale has been described by Schumb,21 and on a technical scale by Porter.28 The initial product of combustion is contaminated with lower fluorides with the highly toxic S2F1,, and with hydrogen fluoride.After an alkaline wash the gases are passed through a heated metal tube to decompose other impurities again alkali-washed before drying and compressing into cylinders. The chlorine fluorides were only discovered some twenty years ago and 45 Compt. rend. 1800 110 951. ** l b i d . 1926 182 1340 ; 1930 191 930. 4 7 2. anorg. Chem. 1930 192 249 49 W. W. Buechner R. J. Van de Graaff A. Sporduto L. R. Macintosh and E. A. 4 8 J . Awaer. Chem. SOC. 1939 61 2962. Burrill Rev. Sci. Instr. 1947 18 754. LEECH PRODUCTION OF FLUORINE 35 during the war the trifluoride especially underwent some development.Ruff et aZ.50 in 1928 reported that the action of fluorine on hydrogen chloride a t liquid-air temperature led to the formation of chlorine monofluoride boiling a t - 103". K. Freclenhagen and 0. Krefft 51 showed that an equimolecular mixture of fluorine and chlorine exploded on sparking and Ruff 52 stated that fluorine readily burns in chlorine. Then in 1930 Ruff and H. Krug53 showed that fluorine and chlorine mixed in the proportion of 1 3 combined gently when heated to about 300" to give the trifluoride ClF, b.p. 11.3". This is a very reactive material in many reactions simi- lar to fluorine itself. The fluorine made in the O.K.H. cells at Falkenhagcn was entirely converted into chlorine trifluoride which was to be empioyed apparently as an incendiary agent in a manner not clearly indicated.The very violent reaction which chlorine trifluoride shows with water and organic matter would appear to make i t fairly effective for incendiary purposes whilst like fluorine itself it can readily be handled in steel or other metal equip- ment ; and unlike bottled fluorine chlorine trifluoride does not develop a high pressure in containers and there is therefore not the same risk of uiicontrollable escape. In the manufacturing process described fluorine from the cells is mixed with three times its volume of chlorine in stages in the first stage on heating to ZOO" the monofluoride is formed and finally the trifluoride is formed a t 250-280". The reaction vessels are nickel throughout with shell-and-tube heat exchangers cooled with air when the reaction is proceeding normally The chlorine trifluoride is condensed out by cooling and stored in steel vessels of 5 m.capacity. The efficiency of conversion of fluorine into the trifluoride is 95%. Chlorine trifluoride is also stated to be one of the products made from the fluorine from the Pennsylvania Salt Mfg. Co.'s cell already described,28 by a process similar to the German. It is stated that under controlled conditions reaction of chlorine trifluoride with organic compounds leads to the introduction of both fluorine and chlorine into the organic molecule. The possibility of using higher fluorides such as cobalt trifluoride as fluorine carriers had been proposed before the war by Ruff. The American fluorocarbon production led to a very considerable development of this technique and e.g.Fowler has considered the various fluorides which may be used. Cobalt trifluoride was principally used manganese trifluoride and silver difluoride to a less extent the latter largely by McBee and his school. These higher fluorides are relatively stable compounds in themselves made by the action of fluorine at somewhat elevated temperatures (200-400") on lower fluorides or chlorides. They yield up their fluorine in a controlled manner to organic materials in the liquid or the vapour state a t tem- peratures from 150" to 400". These compounds may find many uses for laboratories whose fluorine requirements hardly justify the installation of a fluorine cell and their post-war production has been referred to by Porter.2* 6o 0. Ruff E. Ascher J. Fischer and F. Lanss 2. nnorg. Chem. 1928 1'96,258. 61 2. physikal. Chem. 1929 141 221. 6aZ. angew. Chem. 1929 42 807. 63 2. anorg. Chem. 1930 190 270. Little work has been reported on these compunds.

ISSN:0009-2681    

DOI:10.1039/QR9490300022

出版商:RSC    

年代:1949

数据来源: RSC

摘要:

THE CHEMISTRY OF THE DITERPENOIDS By D. H. R. BARTON PH.D. E.R.I.C. (IMPERIAL CHEMICAL INDUSTRIES RESEARCH FELLOW IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY LONDON S.W.7) ALTHOUGH impure specimens of abietic acid and the primary resin acids were the subject of investigations more than a century ago a full understanding of the chemistry of the diterpenoids has been developed only in the last twenty years. This period has seen remarkably rapid progress and apart from certain minor points of stereochemistry the structures of all the majcr diterpenoids have now been elucidated with certainty. The importance of the method of dehydrogenation in establishing the nature of the carbon skeleton in sesquiterpenoid compounds is well known. This method is of even greater importance in the study of diterpenoids and the whole chemistry of the group depends upon basic experiments involving dehydrogenation to aromatic compounds.Indeed the first application of the dehydrogenation method was made in the diterpenoid field by A. Vesterberg who obtained retene (I) from abietic acid by heating it with sulphur. Retene was later isolated in a similar manner by the dehydrogenation of levopimaric acid. A different derivative of phen- anthrene called pimanthrene 1 7-dimethylphenanthrene (11) was first obtained by L. Ruzicka and Balas by the dehydrogenation of dextro- pimaric acid and this hydrocarbon results also usually together with other hydrocarbons from the dehydrogenation of a number of other diterpenoids. The most numerous group of diterpenoids gives either on direct dehydro- genation or dehydrogenation of suitable derivatives 1 7 $-trimethyl- phenanthrene which was first obtained in this way by L.Ruzicka and J. R. Hosking It is possible to make a clmsification of diterpenoids (omitting phytol and a few miscellaneous diterpenoids) into bicyclic and tricyclic groups but since the members of the bicyclic group after suitable cyclisation give the same dehydrogenation products as do those of the tricyclic group it would seem preferable to adopt a system based purely on dehydrogenation experiments as has been done in the case of sesquiterpene compound^.^ One must distinguish therefore three main classes of diterpenoid those giving retene those giving pimanthrene and those giving 1 7 $-trimethyl- phenanthrene recognising also that a number of diterpenoids give both pimanthrene and 1 7 8-trimethylphenanthrene.from a derivative of agathenedicarboxylic acid. Ber. 1903 36 4200. a L. Ruzicka Balas and Vilim Heh. Chim. Acta 1924 7 458. 3 1 b i d . 1923 6 677. ‘ I b i d . 1931 14 203. (1 J. L. Simonsen and D. H. R. Barton “ Tho Terpenes ” Vol. 111 Cambridge Univ. Press. 36 37 The structures of retene pimanthrene and 1 7 8-trimethylphen- BARTON THE CHEMISTRY OF THE DITERPENOIDS anthrene have been rigidly proved by synthesis.6 (6 All the diterpenoids whose constitutions have so far been elucidated obey the " isoprene rule " as illustrated by the formule for abietic acid (111) dextropimaric acid (IV) and agatbenedicarboxylic acid (V). Diterpenoid Resin Acids."-These acids constitute the major non-volatile portion of many oleoresins especially those obtained from conifers.Abietic acid the best known of the resin acids is prepared from colophony (rosin) by treatment with acidic reagents.' .It is a so-called " secondary " resin acid being formed from a precursor levopimaric acid by isomerisation. Dextropimaric acid is also present in colophony but is most easily isolated from French " galipot " * obtained from the cluster pine (Pinus pinaster ; P. maritima). Fossil rosins are formed when resin-exuding trees decay under anaerobic conditions. The copal and kauri copal of various tropical trees are obtained largely as fossilised material and yield the diterpenoid 6R. D. Haworth B. M. Letsky and C. R. Mavin J . 1932 1784; J. C. Bardhan and S. C. Senguipta ibid. p. 2520 ; R. D. Haworth and C. R. Mavin ibid. p. 2720. G.Dupont Bull. SOC. chirn. 1921 29 727 1924 35 879 ; G. Dupont and It. Uzac ibid. 1924 35 394 ; L. L. Steela J . Amer. Chem. SOC. 1922 44 1333 ; 8. Pulkin and T. H. Harris ibid. 1934 55 1935 ; G. C. Harris and T. F. Sanderson ibid. 1948 70 334. * Galipot is that portion oE the untreated oleoresin which crpstallises spontaneously on standing at room t'emperature. Cf. G. C. Harris J . Amer. Chem. Xoc. 1948 70 3671. 38 QUARTERLY REVIEWS resin acid agathenedicarboxylic acid. Many fossil rosins from decayed pine trees have been examined and in the majority of cases the presence of retene and fichtelite (p. 60) has been established Abietie acid which may be obtained in a state of purity by crystallisation of the quarter sodium salt or with greater efficiency of the salts it gives with various nmines sa especially diamylamiize,s is a doubly unsaturated tricyclic acid C20H3002.The two ethylenic linkages are in conjugation lo and although abietic acid gives the same philodiene adduots as levopimaric acid,l0 l1 they must be distributed in two different rings as shown by the ultraviolet absorption spectrum.12 As mentioned above abietic acid (VI ; R = H) gives retene in high yield on dehydrogenation. The carboxyl group which is eliminated in this reaction has been shown to be tertiary in character l3 and t o he attached a t the l-position in the retenoid skeleton. The evidence for this is briefly summarised as follows. Bouveault-Blanc reduction of methyl abietate (VI ; R = Me) afforded abietinol (VII) dehydrated by phosphorus penta- chloride to methylabietin CZoH30.Tlie latter gave homoretene on dehydro- genation with sulphur or ~e1enium.l~ Although homoretene was a t first considered to be a dimethylisopropylphennnthrene it was subsequentlly realised l5 that the formation of methylabietin (VIII) from abietinol involved a molecular rearrangement and that homoretene was 1 -ethyl-’l-isopropyl- phenanthrene (IX). This was confirmed by R. D. Haworth’s synthesis of homoretene. l6 An important clue to the position of the double bonds in abietic acid was furnished a t an early date by the observation that trimellitic acid (X) was produced by oxidation with a variety of reagents.l7 Having regard to * G. Dapont L. Dzsdbres and A. Bernette Bull. SOC. chim. 1926 39 48s ; C. C. Keslor A. Lowy and W. F. Faragher J . Amer. Chem. Soc. 1927 49 2898 ; S. Pellrin and T.K. Harri? loc. cit. ref. (7). F. galas &sopis Cesk. Ldkarnictua 1027 7 320 ; S. Palkin and T. H. Harris Eoc. cit. ; compare V. N. Krestinskii and I. I. Bardyshev J . Gen. Chem. U.S.S.R. 1940 10 1894 ; I. I. Bardyshev ibid. 1941 11 996 ; R. Lombard and J.-31. Frey Bull. SOC. chinz. 1948 15 1194. G. C. Harris and T. F. Sanderson loc. c i t . ref. (7). Abietic acid. lo L. F. Fiesor and W. P. Campbell J . Amer. Chem. Soc. 1935 60 159. 11 L. Euzicka P. J. Ankersmit and R. Frank Helv. Chirn. Acta 1932 15 1289 ; B. A. Arbusow J . Oen. Chem. U.S.S.R. 1932 2 806 ; compare €1. Wimhaus and W. Sandermann Ber. P936 69 2202 ; L. Ruziclra R. G. R. Bacon R. Lukes and J. D. Eoso Helv. Chim. Actu 1938 21 583. l 2 K. Kraft Annalen 1035 520 133 ; H. Wienhaus H. Ritter and W. Sttndermann Ber.1936 69 2108 ; L. Ruzicka and L. Sternbach Helv. Chim. Actn 1938 21 565 ; W. Snndarmann Ber. 1941 74 154. 13W. Fahrion 2. angew. Chem. 1901 14 1197; P. Levy 2. anory. Chem. 1913 81 147. 14 L. Ruzickn and J. Meyer Helu. Chim. ,4cta 1022 5 681 ; L. Ruzicka and H. Jacobs Rec. Trav. chirn. 1038 57 509. * 5 F. Vocke Annalen 1932 497 247 ; I,. Ruzicka G. I3. R. de Graaff and H. J. Muller Helv. Chim. Acta 1932 15 1300. l7 J. Schreder Annalen 1874 172 93 ; 0. Emmefling Rer. 1879 12 1441 ; L. Ruzicka H. Schinz and J. Meyer Helv. Chirn. Actn 1923 6 1077 ; L. Ruzicka and M. Pfeiffer ibid. 1925 8 632. l6 J. 1932 2717. BARTON THE CHEMISTRY OF THE DITERPENOIDS 39 the formula of retene this was taken to imply that at least one of the ethylenic linkages must be in ring B. Support for this view was the fact that isobutpic acid could be obtained on energet,ic oxidation with potassium permanganate.la Rigid proof of the position of the conjugated ethylenic (VIT.) linkages as shown in (VI) has been provided f (VTII.) VX.1 only comparatively recently by the elegant experiments of L.Ruziclra and L. Sternbach.lg When abietic acid is oxidised under mild conditions the fist product of the reaction is dihydroxyabietic acid (XI),2o which then appears to be further attacked with formation of oxidodihydroxyabietic acid (XII). This oxide is unstable in aqueous media and is rapidly hydrated to y-tetrahydroxyabietic acid.* By treatment with dilute hydrochloric acid the latter was converted almost quantitatively into the stable chlorotrihydroxyabietic acid (XIII) whilst with dilute sulphuric acid it afforded the a-tetrahydroxyabietic acid (XIV) which had been obtained previously by P.Levy. 21 y-Tefrahydroxyabietic acid underwent a slow mutsrotation in neutral aqueous solution to afford @-tetrahydroxyabietic acid converted like the y-isomer into the a-acid with dilute sulphuric acid. It appears therefore that the usual product isolated from the potassium permanganate oxidation of abietic acid under mild conditions is a mixture of dihydroxyabietic acid and y-tetrahydrosy- abietic acid and that Levy’s a-tetrahydroxyabietic acid is an artefact formed l 8 P. Levy Ber. 1909 42 4305 ; L. Ruzicka J. Meyer and M. Pfeiffor Hel?]. lS Helv. Chim. Acta 1935 21 565 ; 1940 23 333 341 355 ; 1811 24 492 ; 1942 2O L. Ruzicka and J. &Toyer ibid. 1923 6 1097 ; comparo 0.Aschan Bes.. 1921 21 Ber. 1909 42 4305 ; 1926 59 1302 ; 1935 61 616 ; 1929 62 2497 ; compare * Strictly this name is incorrect and should be replacod by y-tetrahyclroxytetre- Similarly many of the other names uscci in this article are logically Chim. Acta 1925 8 637 ; L. F. Fieser and W. P. Campbell Zoc. cit. ref. (10). 25 1036; L. IZuzickn L. Sternbach and 0. Jogor ibid. 1941 24 504. 54 867 ; L. Ruzicka J. Moyer and M. Pfeiffcr Zoc. cit. rof. (18). 0. Aschan and P. Levy ibid. 1927 60 1923. hydroabietic acid. incorrect but are retained because of the familiar usago in the literatiire. 40 QUARTERLY REVIEWS during working up. Both the p- and the y-tetrahydroxyabietic acid mus% be regarded merely as stereoisomers of the a-acid. By dehydrogenation (XI) (XII) (XIII) and (XIV) all gave 7-hydroxy-1-methylphenanthrene (XV).These experiments place with certainty one of the hydroxyl groups in all these compounds at C arid thus prove the relative position of the isopropyl group and one of the ethylenic linkages in abietic acid. (XI.) (XII.) (XIII.) OT Pd/C I y-Tetrahydroxyabietic acid 130°C I I v\- I (XV.) (XIV.) When y-tetrahydroxyabietic acid was treated with hydrobromic or hydriodic acid it gave bromo- (XVI) or iodo-trihydroxyabietic acid (XVII) respectively. All three halogenot'rihydroxyabietic acids afforded the cor- responding halogenodiketo-acids (XVIII) (XIX) and (XX) on oxidation with two molecular proportions of lead tetra-acetate. With hydriodic acid (XX) was reduced to the diketo-acid (XXI) which by treatment with ammonia gave presumably via the dihydropyridine (XXII) followed by disproportionation 8-azadehydroabietic acid (XXIII) .Selenium dehydro- genation of the latter furnished 8-azaretene (XXIV) the identity of which was confirmed by its synthesis. Both (XIX) and (XX) underwent an unusual reaction when treated with ammonia giving 9-keto-8-azadehydro- abietic acid (XXV) from which (XXIII) was obtained on reduckion by the Wolff-Kishner method. This last series of reactions proves in a particularly elegant manner the correctness of the double bond positions in the abietic acid formula (VI ; R = H). The experiment's described above constitute an unambiguous proof of the main structural features of the abietic acid molecule and leave undecided only the position of the quaternary methyl group. The following is the more important evidencf with regard to this feature.By energetic oxidation abietic acid affords two homologous tricarboxylic acids (XXVI) BARTON THE CHEMISTRY OF THE DITERPENOIDS 41 HO,C HO,C (XILI) Pb(OAc) .1 HO,C X A 7 LIyO CO-CHMe v (xvm.) b\ I N I II \A 1 (XVI.) Pb( OA& or CrO 1 yyTr KO,C v'\Qo.IHnm (XIX.) NH3 (XXV.) Wolff-Kishner 1 HO,C Se I (XVII. ) I Pb(Obc) ( X X . ) HO,C i.' \/ PPI \/)A* ( ,CO*CHTUe (XXI.) HO,C \/\- I I ' (XXIV. ) (XXIII . ) (XXII.) and (XXVII). 22 Dehydrogenation of these with selenium gave respectively m-xylene (XXVIII) and hernimellitene (XXIX). This proves the 1 3- relationship of the two methyl groups in (XXVI) and (XXVII) and hence the position of the quaternary methyl group in (VI) as shown? A further proof of this relationship was provided by L.Ruzicka and zz L. Ruzicka J. Meyer and M. Pfeiffer Eoc. cit. ref. (18) ; P. Levy Ber. 1829 62 2497 ; L. Ruzicka 3%. W. Goldberg H. W. Huyser and C. F. Seidel Helw. Chirn. Acta 1931 14 545 ; compare. J. Schreder Zoc. cit. ; 0. Emmerling Zoc. cit. ; P. Levy loc. cit. ; 0. Aschan and P. Levy loc. cit. 23 L. Ruzicka M. W. Goldberg H. W. Hiiyser a.nd C. F. Seidel loc. cit. 42 QUARTERLY REVIEWS H. Waldmann,24 who showed that vigorous oxidation of abietic acid also afforded 1 3-dimethylcycZohexan-2-one (XXX). HO,C HO,C \/ CH,.CO,R >-<,,co2H /\/ + &I\ ise (171 ; R = €1) -+ I A 1 CO,H ‘+I\ CO,R IiNnO4 (XXV1.) (xx1711.) I be f) I 0.‘ \ \ (XXIX. ) I I,,*” v\ (XXVIII. ) I -4 v\ (XXX.) Additional evidence on this point was given by F. Vocke z5 who treated (XXVI) with red phosphorus and broiiiine and isolated amongst other product’s two bromo-anhydrides (XXXI) and (XXXII) both of which furnished an unsaturated acid (XXXIII) with sodium hydroxide.Although at the time these experiments were carried out they were open to a different interpretation,2G H. N. Rydon’s synthesis 27 of (XXXIII) has confirmed Vocke’s formulation. H02C ErOC H0,C \/ Br \,,/ Br I CO,H \/ <‘+I (p/ ( y > O \/\ C0,H ‘\/I\() / ~ c o \ o + p c o v’- / \/\- I (XXXI . ) (XXXII.) (XXXIII.) (XXXIV.) Levopimaric acid.* This resin acid was first isolated in a state of purity by A. Vesterberg,28 but little progress was made with it,s chemistry until GI-. Dupont 29 had described a reliable method for its preparatioii from French galipot. The most convenient inefhod of isolation is by crystallisa- tion of the butanolamine salt.g S.Palkin and T. H. Harris 30 isolated pure levopimaric acid from the primary resin acids of Pinus paZ,iistl-is and of P. caribhea and it is now certain that the acid is a primary constituent of all resins from pine and fir trees. It has also been shown that the so-called Helv. Chim. Acta 1933 16 842. 25 L O C . cit. 26 L. Ruzicka H. Waldmann P. J. Meier and H. Hosli Helu. Chim. Acta 1933 2 7 J. 1937 257. Ber. 1887 20 3248 29 Comnpt. rend. 1921 172 923 1184 ; Bull. SOC. chim. 1921 29 718 ; compare L. Ruzicka and Balm Zoc. cit. ; L. Ruzicka Balzs and Vilim loc. cit. 30 J . Amer. Chem. Xoc. 1935 55 3677. * The names levo- and dextro-pimaric acid do not of course denote optical anti . 16 169. podes. here because t o do so at this stage might prove confusing.They were originally introduced by A. Vesterberg and have not been altered BARTON THE CHEMISTRY OF THE DITERPENOIDS 43 sapinic acids formerly thought to be primary constituent's of the oleoresin all contain levopimaric acid. 31 * Levopimaric acid C,,H,,O (XXXIV) is readily isornerised by heat or by acids to abietic acid 32 and like abietic acid it gives retene on dehy- dr~genation.~~ The presence of two double bonds and therefore of three rings as implied by the above observations has been proved by hydrogena- tion 34 and by per-acid t i t r a t i ~ n . ~ ~ In addition the two double bonds must be in conjugation for levopimaric acid reacts quantitatrively with maleic anhydride at room temperature to afford the same adduct as is obtained from abietic acid under more vigorous condjtions.38 Since levopimaric acid shows an absorption maximum in the ultraviolet at 272.5 mp,37 it follows that these two conjugated ethylenic linkages must be contained in one ring as indeed would be expected from the ease of addition of maleic anhydride. Levopirnaric acid gives isobutyric acid on ozonolysis. 38 Therefore it is probable that the isopropyl grouping is attached directly to one of the ethylenic linkages. This has been rigidly proved by the elegant experiments of L. Ruzicka and S. Kaufinan~i,~~ the most important of which may be briefly summarised as follows. Ozonolysis of the trimethyl ester (XXXV) derived from the malsic anhydride adduct of levopimaric acid gave amongst other products a mono-unsaturated keto-tricarboxylic acid trimethyl ester (XXXVI) in which the double bond was in the 0r.P-posi- tion to the keto-group as shown by the ultraviolet absorption spectrum.On oxidation with hypobromite (XXXVI) was smoothly degraded (and hydrolysed) to an ap-unsaturated acid (XXXVII) the absorption spectrum of the tetramethyl ester of which confirmed the double bond position in (XSXV). Rigid chemical proof that the acetyl grouping of (XXXVI) was formed from the isopropyl group was obtained (a;) by Clemmensen reduction to (XXXVIII) followed by dehydrogenation to 1 -mcthyl-7-ethyl- phenantltirene (XXXIX) and ( b ) by reaction with ethylmagnesium iodide to give (XL),? dehydrogenation of which afforded l-rnethyl-7-sec.-butyl- 3 1 T. Hmselstrom and M. T. Bogert ibid. 1935 57 211s ; K. Kraft Annulen 1935 520 133 ; 1936 524 1 ; G. C. Harris and J.Sparks J . Amer. Chem. Soc. 1948 70 3674 ; compare F. Voclre Annnlen 1933 508 11 ; W. Sandcrmann Ber. 1938 71 2005. 3 = Inter id. G. Dupoilt Conapt. rend. 1921 172 923 1373 ; Bull. SOC. ckim 1921 29 718 727 ; L. Ruzicka Bslas and Vilim loc c i t . ; R. Lombcrd Bull. SOC. chirn 19-18 15 1186. 33 Idem. ibid. ; W. Sandermann Ber. 1941 74 164. 84 L. Ruzicka and R. G. R. Bacon Helv. Chinz. Acta 1937 20 1542 ; compare L. Ruzicka Ralns and Vilim Zoc. cit. 36 B. A. Arbusow Zoc. cit. ; L. Ruzicka P. J. An!rersmit and B. Frank Zoc. cit. ; L. Ruzicka aiid R. G. R. Bacon Zoc. cit. ; H. Wienhaus and W. Sandermann Ber 1936 69 2202. 35 I<. Kraft Annalen 1036 524 1. 37 K. &aft Anizalen 1935 520 138 ; G. C. Harris and T. F. Sanderson loc. cit s* L. Ruzicka R. G. R. Bacon R. Lukes and J.D. Rose Zoc. c i t . 3* Helv. Chim. Actn 1940 23 1346 ; 1941 24 939. * R. Lombard's recently isolated dextrosapinic acid may be an exception to thk; ?The carbomethoxyl groupings in (XXXVI) may also have reacted with the generalisation (p. 45). Grjgnard reagent but this does not affect the argnment. 44 QUUTERLY REVIEWS Me0,C \ / K A n (XXXVII.) r c o z M e - I C H C H . C O BMe" (XXXVIII.) I (XLII . ) (XXXIX. ) LVI . ) Zn/HCI MgEtI (XLI.) phenanthrene (XLI). The formation of (XXXIX) and (XLI) shows beyond doubt that the double bond of the adduct (XXXV) must be adjacent to the isopropyl grouping. Only the formulz (XXXIV) and (XLII) therefore are possible representations of levopimaric acid and of these the former is much to be preferred as it explains more readily the ease of rearrangement to abietic acid.The formula (XXXIV) is also supported by various theoretical arguments which have been advanced by W. Sandermann. 40 * This interesting resin acid is a primary constituent of the oleoresin of Pinus palusiris and has been isolated therefrom as the 40 Ber. 1941,74 154 ; W. Sanclermann and R. Hohn ibid. 1943 '76 1257 ; compare L. Ruzicka and S. Kaufmann Helv. Chim. Acta 1941 24 1425. 41 Chem. Zentr. 1942 ii 892 893. * Formula (XXXIV) for levopimaric acid is said to be provocl by certain experiments of B. A. ArbusomT,41 who has shown that the a-naphthaquinone adduct on dehydro- genation with air in alcoholic potash solution followed by pyrolysis and then oxidation with nitric acid affords anthraquinone- 1 3-dicarboxylic acid. The Reviewer has not ha? arcess t o Arbusow's original memoirs.neoAbietic acid. BARTON THE CHEMISTRY OF THE DITERPENOIDS 46 butanolamine salt by G. C. Harris and T. F. Sanderso~i,*~ as well as from the resin of this tree. It is also conveniently prepared by heating abietic acid at 300" in an inert atmosphere for short periods. The structure of neoabietic acid as (XLIII) has been established by G. C. Harris and T. F. Sanderson 43 in the following way. neoAbietic acid gave retene on dehydro- genation absorbed two molecular proportions of hydrogen on catalytic hydrogenation showed an intense band in the ultraviolet at 250mp and like levopimaric acid was almost quantitatively isomerised to abietic acid by the action of mineral acid. It must therefore be a simple double-bond isomer of abietic acid in which the double bonds are in conjugation with each other but not in the same ring of the carbon skeleton.On ozonolysis neoabietic acid afforded acetone and an ag-unsaturated ketone C1,H,,O (XLIV) thus showing the presence of an isopropylidene group. It was possible to distinguish between the alternative formula? (XLIII) and (XLV) both of which explain this observation since drastic ozonolysis of neoa,bietic I (XLIII. ) o* d (energetic) I CO*CO,H \/ (XLVa . ) I 1 (XLV.) (XLVb.) acid and dehydrogenation of the reaction product presumably (XLVa) gave 1- methyl- 5 - n-prop ylnapht halene (XLVb) . The relationship of neoabietic acid to t'he dextrosapinic acid recently isolated by R. Lombard 44 as a primary constituer;t of the galipot of Pinus halepensis is uncertain but like neoabietic acid dextrosapinic acid is said to be isomerised by acids to abietic acid.This acid was f i s t obtained in a state of purity by A. Vesterberg 45 by crystallisation of the sparingly soluble sodium salt but it is best isolated after removal of levopimaric acid as the maleic anhydride adduct by crystallisation of the butanolamine salt. 48 Dextro- pimaric acid is probably present to a greater or less extent in all resins 4 2 L O C . cit. 44 Compt. rend. 1944 219 587 ; 1944 219 253 ; 1946 222 237 ; Bull. Xoc. c l z i m 1945 12 395. 46 Ber. 1885 18 3331 ; 1886 19 2167 ; compare idem ibid. 1887 20 3248 ; 1905 38 4125 ; G. Dupont Bull. SOC. chim. 1921 29 718 ; L. Ruzicka and Balas Zoc. cit. ; L. Ruzicka Bdas and Vilim Zoc. cit. Dextropimaric acid. 4 9 J . Amer. Chem. Soc. 1948 'SO 339. 46G.C. Harris and T. F. Sanderson J . Amer. Chem. SOC. 1948 70. 2079. 46 QUARTERLY REVIEWS obtained from conifers but it is not alwa.ys possible to separate it from the accompanying isomeric resin acids. Thus it has been detected in the resins from Pinus caribbea P. tzda P. serotina and Picec excelsa,47 as well as in the oleoresins of P. palustris 4* and P. syl~estris.~~ Unlike most of the other primary resin acids dextropimaric acid is comparatively stable to heat and is not isomerised by treatment with mineral acids. As mentioned above (p. 36) dextropimaric acid (XLVI) gives piman- threne (XI) on dehydrogenation. The position of the carboxyl group has been proved by a similar series of experiments to those recorded (p. 38) for abietic acid. Thus Bouvcault-Blanc reduction of ethyl pimarate afforded dextropimarinol dehydrated by phosphorus pentachloride to methyl dextropimarin which on dehydrogenation gave an aroinatic hydrocarbon C,,H,,.Although the lat'ter was a t first considered to be a trimethyl- phenanthrene it was subsequently shown by 1;. Ruzicka G. B. R. de Graaff and H. J. &Iuller,51 to be 7-methyl-l-ethylphenanthrene (XLVII) and this identity has been confirmed by synthesis.52 From this it follows that niethyldextropimarin must be represented by (XLVIII) its formation involving a rearrangement similar to that observed in the dehydration of abietinol." A further indication of the position of the carboxyl group and a proof of the points of aktachment of the two quaternary methyl groups in ring A are that vigorous oxidation of dextropimaric acid gives the same two tricarboxylic acids (XXVI) and (XXVII) as are obtained in the same way from abietic acid (p.40).53 (XLVI.) (XLVII.) (XLVIII.) Dextropimaric acid is doubly unsaturated a>s shown by catalytic hydro- genation 54 and by per-acid experiment~.~~9 55 Since it has the formula C,,H,,O it must be tricyclic in agreement with the dehydrogenation evidence. The two double bonds are not in conjugation and differ greatly 47 Inter al. T. Hasselstrom and M . T. Bogert loc. cit. ; K. Kraft Annalen 1935 520 133 ; 1936 524 1 ; W. Sandermann Ber. 1938 71 2005 ; 1942 75 174. 48 S. Palkin and T. H. Harris loc. c i t . ; K . Kraft Zoc. cit. 49A. Vesterberg Ber. 1905 38 4125. 60 L. Ruzicka and Balas Helv. Chin&. Acta 1924 7 875. i51 L O C . cit. 62R. D. Haworth J . 1932 2717.6 3 L. Ruzicka G. B. R. de Graaff M. W. Goldberg and B. Frank Helv. Chini. Actci 6 4 L. Ruzicka H. W. Huyser and C . F. Seidel Rec. Trav. chim. 1928 47 363. 5 6 L. Ruziclre and B. Frank Helv. Chim. Acta 1932 15 1294 ; K. Kraft Annulem 1936 524 1 ; L. Ruzicka and L. Sternbach Helv. Ghim. Actcc 1940 23 124. * It should be pointed out that the 1 (2)-position of the ethylenic linkage in methyl- dextropimarin and in methylabietin has not been proved and it may well be at l(11) instead. 1932 15 915. BARTON THE CHEMISTRY OV THE DITERPENOIDS 47 in reactivity. Partial hydrogenation gives a very insoluble and characteristic dihydrodextropimaric acid (XLIX),54 56 which has been used by L. Ruzicka and L. Sternbach 57 in an elegant demonstration that the less reactive double bond is in the 7(8) or S(14)-position.Their evidence is briefly as follows. By treatment of the oxide of methyl dihydrodextropimarate (L) with methyl- magnesium iodide an alcohol (LI) was prepared which on dehydrogenation gave 1 7 8-trimethylphenanthrene (LII). MgMeI I' (XLIX. ) (LII.) The more reactive of the two ethylenic linkages is present as a tertiary vinyl grouping. This is proved by the facts that dext,ropimaric acid may be oxidised by potassium permanganate to a glycol (LIII) which on further oxidation by chromic acid gives a dicarboxyiic acid C,,H,,O (LIV) con- taining one carbon atom less,58 which is dehydrogenated by selenium to pimanthrene (11). 53 As would be expected ozonolysis of dextropimaric acid gives a high yield of f~rmaldehyde.~~ (LIII. ) (LIV.) (11.1 The experiments described above taken in conjunction with the " isoprene rule " indicate that dextropimaric acid must be represented by either (XLVI) or (LV).Conclusive evidence in favour of the former 6 6 L. Ruzicka and Balas ibid. 1923 6 681 ; L. Ruzicka and B. Frank Zoc. cit. ; S . Palkin and T. H. Harris loc. c i t . ; T. Hasselstrom and M. T. Bogert Zoc. cit. ; compare L. Tschugaeff and P. Teearu Ber. 1913 46 1773. 5 7 LOC. cit. 68 I,. Ruzicka and Balas Annakn 1928 460 202 ; compare P. Levy Ber. 1928 61 616. so L. Ruzicka and Balas Zoc. cit. ; compare L. Kuzicka C. E'. Soidel IT. Schinz and M. Pfeiffer Helv. Chim. Acta 1947 30 1807. 48 QUARTERLY REVIEWS of these has been reported recently by G. C. Harris and T. F. Sanderson.60 Dihydrodextropimaric acid (XLIX) was ozonised to give the keto-aldehyde (LVI) (negative iodoform test) which was reduced by the Wolff-Kishner method and then dehydrogenated to give a CIS disubstituted naphthalene (LVII).The keto-aldehyde from (LV) would have given a positive iodoform test and would have been converted into a C, trisubstituted naphthalene. Further proof for the correctness of (XLVI) was provided by partial dehydro- genation of dext,ropimaric acid which gave a C, trisubstituted naphthalene (LVIII). (XLVI.) (XLIX.) I I (LV.) I I a).. - I I/- \/\ (LVIII.) I 0 3 PdjC (LVIZ.) (LVI.) isoDextropimaric acid. This interesting resin acid has been isolated recently 46 as the butanolamine salt during the preparation of dextropimaric acid. G. C. Harris and T. F. Sanderson Go regard it as the C epimeride of dextropimaric acid on the basis of the following evidence.When isodextro- pimaric acid was subjected to the same series of degradations as was applied to dextropimaric acid the same hydrocarbons (LVII) and (LVIII) were obtained racemisation at C being presumed to occur during the formation of (LVIII). Also when dextropirnaric acid and isodextropimaric acid were ozonised and the products oxidised with hydrogen peroxide the same tricarboxylic acid (LIX) in which the asymmetry at C had been destroyed was isolated in both cases. Although Harris and Sanderson's interpretation of the experimental evidence is logical it should be pointed out that isodextropirnaric acid and its butanolamine salt were found to be optically inactive in all solvents and to This would be unexpected unless it were the racemate corre- sponding to dextropimaric acid.give an optically inactive dihydro-acid. 6 CO,H (LIX.) G. C. Harris and T. F. Sanderson60" have also 6o J . Amer. Chem. Soc. 1948 70 2081. 6ofJ Ibid. p. 3870. BARTON THE CHEMISTRY OF THE DITERPENOIDS 49 isolated the aldehyde corresponding to isodextropimaric acid from the neutral fract'ions of commercial gum and wood rosins. It is probably identical with cryptopinone obtained by N. A. Sorenseii and T. Bruun 60b from the twig roots and resinified trunks of pine trees. This bicyclic resin acid was first isolated in a state of purity by L. Ruzicka and J. R. Hosking 61 from Kauri copal and from the soft and hard grades of Manila copal. The structure (LX) which has been assigned t o this acid is due entirely to the experiments of L. Ruzicka and his collaborators,62 and is based on the following evidence.The carbon skeleton present in the acid is indicated by its dehydrogenation with sulphur or selenium to give 1 5 6-trimethylnaphthalene (LXI) and pimanthrene (11). The formation of the latter results presumably from the presence of an unsaturated side chain which appears partially in the naphthalene hydrocarbon as a methyl group. The acid contains two ethylenic linkages one of which must be in the ccp-position with respect to one of the carboxyls. This is shown by the absorption spectrum and by the ease wit'h which carbon dioxide is split out on pyrolysis to give noragathenemonocarboxylic acid (LXII) . Agathenedicafboxylic acid. I Ill v\ (LXIII.) (LXV.) (LXIV. ) MgMeI sob Acta chem. scand. 1947 1 112. G 2 L. Razjcka R. Steiger and H.Schinz Helv. Chim. Acta 1926,9 962 ; L. Ruzicka and J. R. Hosking ibid. 1930 18 1402 ; 1931 14 203 ; L. Ruzicka and H. Jacobs Zoc. cit. ; L. Ruzicka E. Bemold and A. Tallichet Helv. Chim. Acta 1941 24 223 ; L. Ruzicka and E. Bernold ibid. p. 931 1167 ; compare L. Ruzicka and E. Rey ibid. 1943 26 2136. 61 Annalen 1929 469 147. r) 50 QUARTERLY REVIEWS The position of the two olefinic linkages in agathenedicarboxylic acid was proved by a study of the ozonolysis products of the dimethyl ester. The most important of these was a 1 5-diketone (LXIII) which readily underwent intramolecular dehydration on treatment with alkali to give a tricyclic ap-unsaturated ketone (LXIV). By reaction with methyl- magnesium iodide," the latter afforded a conjugated diene (LXV) dehydro- genated by selenium to give pimanthrene.These experiments also indicate the position of the carboxyl group which is easily eliminated on pyrolysis. The position of the other carboxyl group was proved in the following manner. When agathenedicarboxylic acid was digested with formic acid it was isomerised to a tricyclic acid isoagathenedicarboxylic acid (LXVI). This like its progenitor possessed an orp-unsaturated carboxyl group readily eliminated by heat to give isonoragathenemonocarboxylic acid (LXVII). Reduction of the methyl ester of the latter t by a modified Bouveault-Blanc (LXVI.) (LXVII.) (LXVIII . ) (XLVII.) method furnished isonoragathenol (LXVIII) which was dehydrated and then dehydrogenated to give 7-methyl- l-ethylphenanthrene (XLVII) identical with the hydrocarbon prepared similarly from dextropimaric acid (p.46). Although podocarpic acid is not strictly a member of the diterpenoid resin acids its chemistry is closely related to that of the diterpenoids. It is convenient therefore to give a short account of it here. Podocarpic acid C,,H,,O (LXIX ; R == H) was first isolated by A. C. Oudemans 63 from the resin of Podocarpus cupressinum and was obtained later 64 from P. dacrydioides and from Dacrydium cupressinum. It is a phenolic carboxylic acid which gives l-methylphenanthrene and 6-hydroxy- Podocarpic acid. a 3 Ber. 1873 6 1122 1125 ; Annalen 1873 170 214 ; J. p r . Chem. 1874 9 385. 64Compare I. R. Sherwood and W. F. Short J. 1938 1006. * The tertiary carbomethoxyl group in (LXIV) is strongly hindered storically and does not react. 7 More recent experiments have shown that (LXVII) was iiot homogeneous ; this does not affect the validity of the conclusions reached here because tho inhomogeneity depended only on isomerism in ring B.BARTON THE CHEMISTRY OF THE DITERPENOIDS 51 1 -methylphenanthrene on dehydr~genation.~~ Although these facts are explicable by other formulae besides (LXIX ; R = H) the correctness of the latter was proved by W. P. Campbell and D. Todd 66 in the following way. Podocarpic acid methyl ether (LXIX ; R = Me) was reduced by the Rosenmund method to podocarpinal methyl ether (LXX) which was further hydrogenated to podocarpinol methyl ether (LXXI). This was dehydrated and then dehydrogenated to give 6-rnethoxy-1 -ethylphenan- threne (LXXII). (LXIX.) (LXX.) (LXXI.) \/ OM0 OMe (LXXII.) Miropinic acid and isomiropinic acid.* These acids were isolated by C .W. Brandt and L. G. Neubauer from the resin exuded by the Miro tree (Podocarpus ferrugineus). Miropinic acid C20H3003 is tricyclic has two ethylenic linkages and gives pimanthrene on dehydrogenation. It is partly isomerised to isomiropinic acid by treatment with methanolic hydrogen chloride. Vouacapenic acid. The heartwood of Vouacapoua americana Aubl. contains the methyl ester of vouacapenic acid C,,H,,O,. This acid has two ethylenic linkages ; the third oxygen atom is probably ethereal.70 Cativic acid. The oleoresin from Prioria copaifera Griseb. (the cativa tree) contains the interesting resin acid cativic acid C20H3402 which occurs in the resin both in the free state and esterified with the corresponding primary alcohol cativyl alcohol.Although cativic acid is probably 6s H. Plimmer W. F. Short and P. Hill ibid. p. 694 ; I. R. Sherwood and W. F. 6 7 J . Pharm. SOC. Japan 1937 57 69. 68 J. R. Hosking and C. W. Brandt Ber. 1935 68 1313 ; J. R. Hosking New 70 D. B. Spoelstra Rec. Trav. china. 1930 49 226. * Mkopinic acid is possibly identical with cryptopimaric acid isolated by S. Keimatsu T. Ishiguro and G. Fukui 6 7 from Gryptomeriajaponica and with an acid obtained from Dacrydium. bqorme and D. birkii.68 Short Eoc. cit. 66 J . Amer. Chem. SOC. 1042 84 928. Zealand J . Sci. Tech. 1937 19 208. 69 J. 1940 683. 52 QUARTERLY REVIEWS diterpenoid it differs from abietic acid and related acids in that its carboxyl group is readily esterfiedO7l Diterpenoid Alcohols and Phenols.-These compounds have received compar at ivelj little at tent io n .Phytol. The mono-unsaturated aliphatic diterpenoid alcohol phytol C2J3400 was discovered by R. Willstatter 7 2 to be the alcoholic moiety of the chlorophyll molecule. The initial degradational experiments 73 did not lead to a successful elucidation of the structure of phytol and this was only effected later by the synthetic experiments of F. G . Fischer,74 who found that phytol (LXXIII) which had been already recognised as a primary alcohol gave a saturated ketone (LXXIV) and glycollic aldehyde on ozonolysis thus showing the double bond to be in the ccp-position to the alcoholic grouping. The structure of (LXXIV) as 2 6 10-trimethyl- H3C CH3 CH CK3 I I I ~~.[C€12]3.CH.[~H*]3.C~~.[CH,I,.C :CH*CII,-OH \ / (LXXIII.) H,C CH3 CH3 I cIr loa H3C I I CXI.[ CH,],*CK.[ CH,],.CH*[ C;H1] C O \ / I5,C (LXXIV.) " Ketuiiic 'I hydrolysis etc.CK3 I t CH3 I CH*[CH,I3.CH*[CH2I3*CH.[CH,I,.Br + CH,-CO*CHNa*CO,Et \ / H3C (LXXV.) pentadecan-14-one was proved by its synthesis as indicated * from hexahydrofarnesyl bromide (LXXV) . Natural phytol usually has a negligibly small optical rotation and this has been taken to imply that it is a r a ~ e m a t e . ~ ~ However Karrer et aE.76 H3C 71 N. L. Kalman J. Amer. Chew. Soc. 1938 60 1423. 7 2 R. Willstatter and F. Hochecler Annden 1907 354 305 ; R. Willstatter F. Hocheder and E. Hug ibid. 1909 371 1 ; R. Wjllstatter and 4. Opp6 ibid. 1911 3'98 1. 7 3 R. Willstatter E. W. Mayer and E. HLini ibid. p. 73 ; R. Willstiitter 0. Schuppli and E. W. Mayer ibid. 1918 418 121. 7 4 Ibid. 1928 464 69 ; F.G. Piselier and K. Lowenborg ibid. 1929 475 183. 7 5 F. G. Fischer and K. Lowenberg doc. cit. ; T. MTagner-Saurogg 2. physiol. Clzetre. '6 P. Kurrer A. Geiger H. Rentschler E. Zbinden and A. Kugler Helv. Chim. Acta * For later syntheses see L. I. Smith and J. A. Sprung J . Arrzer. Cliem. SOC. 1943 1933 222 21. 1943 26 1741. 85 1276; P. Karrer et ul. Helv. Chiin. Acta 1943 26 1741. BARTON THE CHEMISTRY OF THE DITERPENOIDS 53 have recently described the isolation of an optically active phytol [mi:"" + 0 - 2 0 4 4 1 O from nettles and have synthesised a lzevorotatory phytol tcD - 0.18". This synthetic phytol and the dextrorotatory phytol are not as might have been thought optical antipodes ; 77 it is concluded that phytol is not a racemate but a latently optically active compound.The ditertiary glycol sclareol C,,H,,O (LXXVI) was first isolated by Y. Volmar and A. Jermstad 78 from the leaves of Salvia sclarea I;. It was recognised as a diterpenoid by 31. M. J a n ~ t ~ ~ who showed by catalytic hydrogenation to the saturated dihydrosclareol (LXXVII) that it must be bicyclic and contain only one ethylenic linkage. The carbon skeleton of sclareol was partly characterised by L. Ruzicba and M. M. Janot's observa- tion 8O that sclareol gave 1 5 6-trimethylnaphthalene (LXI) on dehydro- genation with selenium. When dihydrosclareol was treated with potassium hydrogen sulphate it furnished amongst other products dihydrocyclo- sclarene (LXXVIII) which was dehydrogenated to a mixture of 1 7 8- trimethylphenanthrene (LII) and pimanthrene.8O The presence of a methylene grouping in sclareol was shown by the high yield of formaldehyde on ozonolysis and by the formation of a CIg dihydroxy-acid (LXXIX) amongst other products on oxidation with potassium permanganate.80.81 In view of these experimental facts particularly the isolation of (LII) on dehydrogenation of (LXXVIII) a carbon skeleton similar to that in agathenedicarboxylic acid (p.49) was suggested. The two uncharacterised oxygen atoms must be present as tertiary alcoholic groups and are placed as indicated in order best to account for the formation of (LXXVIII) on dehydration. Some recent work on manool (p. 55) discussed later con- stitutes an indirect proof of the correctness of the sclareol formula. Sclareol. (LXI.) OH OH (LXXVI.) (LXXVII. ) I OH (LXXIX. ) (LXXVIII.) 7 7 P. Karrer H.Simon and E. Zbinden ibid. 1944 27 313. 78 Compt. rend. 1928 186 517 783. 8oHelv. Chim. Ada 1931 14 645 ; M. M. Janot Ann. Chim. 1932 17 5. 81 L. Ruzicka C. F. Seidel and L. L. Engel HeEv. Chim. Aota 1942 25 621. 7 9 I b i d . 1930 191 847 ; 1931 192 845. 54 QUARTERLY REVIEWS Manool manoyl oxide and ketomanoyl oxide. Because of a very close relationship in structure it is convenient to treat these three substances together. The diterpenoid alcohol manool C,,H,,O (LXXX) was isolated by J. R. Hosking and C. W. Brandt 82 from the wood oil of the yellow pine (Dacrydium biforme). The same authors also reported the isola.tion of manoyl oxide C2,H3,0 (LXXXI),83 and of ketomanoyl oxide (LXXXII)84 from the wood oil of the silver pine (Dacrydium coEensoi ; otherwise D. uiesthndicum).The accepted structure for manoyl oxide was established by Hosking and Brandt 8 5 7 86 in the following manner. Manoyl oxide contained only one ethylenic linkage and the oxygen atom which could not be characterised was assumed correctly to be part of an oxide ring. On dehydrogenation with selenium manoyl oxide afforded 1 5 6-trimethylnaphthalene (LXI) and 1 7 8-trimethylphenanthrene (LII). The presence of an exocyclic methylene group was proved by the formation of formaldehyde in high yield on ozonolysis and by oxidation with potassium permanganate which gave a C, acid (LXXXIII). This acid is important because it shows that (LXXXIV.) the oxide ring in (LXXXI) is correctly formulated. Oil treatment with hydrogen chloride both manoyl oxide and sclareol gave the same trichloro- compound (LXXXIV) thus confirming the structure assigned to the former.The formula (LXXX) for manool was deduced by Hosking and Brandt s2 86 from the following evidence. Since manool gave the same product (LXXXIV) by treatment with hydrogen chloride as was obtained from manoyl oxide they must possess the same carbon skeleton. Catalytic hydrogenation of manool furnished the saturated tetrahydromanool (LXXXV) and thus showed the presence of two ethylenic linkages. The action of hydrogen chloride on (LXXXV) afforded a chloride yielding on digestion with aniline a mixture of two hydrocarbons (LXXXVI) and (LXXXVII). On ozonolysis this mixture gave a C, ketone (LXXXVIII) 8 2 Ber. 1935 68 1311 ; N e w Zealand J. S c i . Tech. 1936 17 755. 83 Ber. 1934 67 1173 ; N e w Zealand J. S c i .Tech. 1936 17 7.50. 84 Ber. 1934 67 1173 ; 1935 68 286 ; N e w Zealand J. Sci. Tech. 1936 17 750. 85 Ber. 1935 68 37. su Ilbid. 1936 69 780. BARTON THE CHEMISTRY O F THE DITERPENOIDS 55 and a c16 acid (LXXXIX). The formation of these two degradation pro- ducts provides conclusive proof that the hydroxyl group in manool must be as in (LXXX) and also indicates indirectly the position of one of the ethylenic linkages as shown. The position I I (LXXXVI.) of the other ethylenic linkage '(XCI.) Vl\A -+ CO,H (h (LXXXIX.) 1 COMe (LXXXVII.) was proved by ozonolysis of manool itself which gave a C, diketone (XC). The keto-groups must have been in the 1 5-relationship in the latter because of the ease with which it was cyclised by alkali to the hydroxy- ketone (XCI). The formula (LXXX) for manool has recently received confirmation by the establishment of a direct relationship with abietic acid.87 The hydroxy-ketone (XCI) was reacted with isopropylmagnesium bromide to give the dihydric alcohol (XCII) which was dehydrated to the corresponding diene possibly (XCIII) and then dehydrogenated by bromosuccinimide to the hydrocarbon (XCIV).This hydrocarbon was identical with dehydro- abietane obtained from abietic acid since both gave the same 6 S-dinitro- dehydroabietane on nitration. The synthesis of dehydroabietane had been carried out earlier by W. P. Campbell and D. Todd,66 starting with dehydro- abietic acid (XCVI).* This was reduced by the Rosenmund method to \/ (LXXXVIII.) 8'0. Jeger 0. Durst and G. Buchi Helv. Chim. Acta 1947 30 1553. *Dehydroabietic acid was first obtained in a state of purity by L.F. Fieser and W. P. Campbell.lo It is a major constituent of the so-called pyroabietic acid formed by the action of heat on abietic acid.10 88 Although much interesting work of a preparative nature has been done in recent years on dehydroabietic z~cid,~g space restrictions do not justify a detailed account here. 56 QUARTERLY REVIEWS clehydroabietinal (XCVII) which on further reduction by the WolE-Kishner method gave dehydroabietane. ’I\/\ OH \ A/\ I (XCIII.) I (XCI‘L. ) 1 (XCIV.) I (XCVI.) (XCVII . ) (XCV.) The forinula (LXXXII) for ketoma,noyl oxide has been elegantly demonstrated by the experiments of Mosking and Brandt .s4 86 Reduction of this oxide by the Wolff-Kishner method afforded rnanoyl oxide (LXXXI) thus leaving only the position of the keto-group to be established.With methylmagnesium iodide (LXXXII) furnished via the carbinol (XCVIII) and catalytic hydrogenation (XCIX) the oxide ring of which was split by hydrogen chloride to give (C). Removal of hydrogen chloride from the latter by heating with aniline followed by dehydrogenation gave ,z mixture of 1 3 5 6-tetramethylnaphthalene (CI) and probably 1 3 7 %tetra- methylphenanthrene (CII) thus proving the original keto-group to have occupied the 3-position. This phenolic diterpenoid comprises the major part of the resin of the Miro tree and was isolated therefrom by C. W. Brandt and L. G. N e u b a ~ e r . ~ ~ Perruginol C20H300 gave 6-hydroxyretene (CIII ; R = a) on dehydrogenation with selenium,g0 91 from which result the formula (CIV) was deduced.The correctness of this formula was shown by W. P. Campbell and D. Todd 66 by partial synthesis of ferruginol (a) from dehydroabietic acid and (b) from podocarpic acid (p. 50). ( a ) 6-Meth- oxydehydroabietic acid (CV) was reduced by the Rosenmund method to Ferruginol. 88Inter al. E. E. Fleck and S. Palkin J . Amer. Chem. SOC. 1937 59 1593; 1938 60 921 ; 1939,61 247 ; L. Ruzicka R. G. R. Bacon L. Sternbmh and H. Waldmsnn Helv. Chim. Acta 1938 21 591 ; R. Lombard Compt. rend. 1939 208 1321 ; 1941 213 793 ; Bull. SOC chim. 1942,9 833 ; T. Hassslstrom E. A. Brennan,!and S. Hopkins J . Amer. Chenz. SOC. 1941 63 1759. a9 Inter nl. T. Hasselstrom E. A. Brennan and J. D. McPherson ibid. 1938 60 1267 ; T. Hasselstrom and J. D. McPherson ibid. p. 2340 ; L. F. Fioser and W. P. Campbell ibid.p. 2631 ; 1939 61 2528 ; W. P. Campbell and M. Morgana ibid. 1941 63 1838 ; T. Hasselstrom and S. Hopkins ibid. p. 421 ; L. Ruzicka and S. Kaufmann Helv. Chim. Acta 1940 23 288. J. 1939 1031. 9lW. P. Campbell and D. Todd J . Amer. Ghem. Soc. 1940 62 1287. BARTON THE CHEMISTRY OF THE DITERPENOIDS 57 (LXXXII. ) (XCVITT.) (XCIX . ) I I XXX I + the corresponding aldehyde which on further reduction by the Wolff- Kishner procedure gave ferruginol. (b) Podocarpic acid methyl ester methyl ether (CVI) underwent the Friedel-Crafts reaction with acetyl chloride to give the 7-acetyl derivative converted by reaction with methyl- magnesium chloride followed by dehydration of the resulting tertiary (CVI.) (CVII. ) (CVIII.) carbinol * into the 7-isopropenyl derivative which on hydrogenation furnished 7-isopropylpodocarpic acid methyl ester methyl ether (CVII).The cor- responding acid was then reduced as described above for 6-methoxyde- hydroabietic acid and gave ferruginol. These partial syntheses are not only a proof of the structure of ferrigunol but also show that the carboxyl group in abietic acid is epimeric to that in podocarpic acid. The diterpenoid phenolic alcohol hinokiol C20H3002 wits Hinokiol. * The carbomethoxyl group of methyl podocarpate is very hindered sterically and did not react wit,h the Grignard reagent. 58 QUARTERLY REVIEWS first isolated by Y. Yoshiki and T. Ishiguro 92 as one of the crystalline constituents of the resin extracted from the heartwood of Chamzcyparis obtusa Sieb. et Zucc. The chemistry of hinokiol has been extensively 93 On dehydrogenation with selenium hinokiol furnished amongst other products a substance which is undoubtedly 6-hydroxyretene (CIII ; R = H),90 91 and which accounts for the phenolic hydroxyl in hinokiol.The second hydroxyl is secondary as shown by oxidation of hinokiol to the corresponding ketone hinokione which is also a constituent of Chamzcyparis obtusa resin. It is probably attached a t the 3-position,94 as shown in the formula (CVITI). The only known phenolic ketone sugiol C,,H2s02 was isolated by S. Keimatsu T. Ishiguro and G. Fukui 95 from Cryptomeria japonica D. Don. Some progress has been made towards the elucidation of its structure.96 On reduction by the Clenimensen method and dehydrogenation of the product sugiol methyl ether afforded a substance which is undoubtedly 6-methoxyretene (CIII ; R = CH,).Sugiol probably differs therefore from hinokione only in the position of the ketonic oxygen function. The diterpenoid alcohol totarol C20H300 isolated from the wood of the totara tree (Podocarpzcs totara) has been investigated by W. F. Short and H. Str~rnberg.~~ Totarol is probably a secondary alcohol and it contains three ethylenic linkages. On dehydrogenation i t gives 7-hydroxy-l- methylphenanthrene which has been synthe~ised.~~ Diterpenoid Hydrocan;bons.-These constitute a numerous group of diterpenoids which apart from camphorene are of unknown structure. They are not a t present of acny economic importance. Camphorene was found by F. W. Semmler and I. Rosen- berg 99 to occur in the higher-boiling hydrocarbon fraction of camphor oil. Later,loO it was recognised as identical with the dimyrcene prepared by C.Harries lo1 by the action of heat on myrcene. It can also be prepared by similar pyrolytic methods from other substances. lo2 Camphorene is monocyclic and has four ethylenic linkages as shown by its catalytic hydrogenation to octahydrocarnphorene (CIX). The latter on oxidation with manganese dioxide and sulphuric acid furnished terephthalic acid. Slcgiol. TotaroE. Camphorene. 92 J . Pharm. SOC. Japan 1933 53 11 ; Chem. Zentr. 1933 i 3203. 93 S. Keimatsu and T. Ishiguro J . Phnrm. SOC. Japan 1935 55 45 ; Chew,. Zentr. 1935 ii 3664 ; G. Huzii and T. Tikamori J . Pharm. Xoc. Japan 1939 59 116. 94 L. F. Fieser and 11. Fieser " The Chemistry of Natural Products related to Phenanthrene " New Edition 1949. The Reviewer is much indebted to Professor L.F. Fieser for an opportunity to read the text of the new edition before pubIication. 95 J . Pharm. SOC. Japan 1937 57 92 ; Chern. Zentr. 1937 ii 596. 9 6 G. Huzii and T. Tikamori J . Phnrm. SOC. Japan 1939 59 124; Chem. Abs. 9SW. F. Short H. Stromberg and A. E. Wiles J . 1936 319. 99Ber. 1913 46 768. 1 o o F . W. Semmler and K. G. Jonas ibid. p. 1566; 19P4 47 2068. 101 Ibid. 1902 35 3264. 102 F. W Semmler and K. G. Jonas ibid. 1914 47 2068 ; 1939 33 4592. 9 7 J . 1937 516. I<. Iiafuku T. Oyamada and M. Nishi J . Chein. SOC. Japan 1933 54 364; L. A. Golclblatt and S. Palkin J . Amer. Chenz. Xoc. 1941 63 3517. BSRTON THE CHEMISTRY OF THE DITERPENOIDS 59 (CIX.) (CX.) (CXI.) (CXII.) This is in agreement with formula (CX) for camphorene lo3 derived from consideration of its method of formation by the polymerisation of myrcene.The diterpene phyllocladene C20H32 has been isolated from numerous essential l o 5 9 log and may occur together with isophyllocladene. lo6 Both phyllocladene and isophyllocladene are tetracyclic and contain one ethylenic linkage. They give the same hydrochloride and are related to each other respectively as are ,8- and cc-pinene. lo5 Phyllocladene gives amongst other products pimanthrene and retene on dehydrogenation and it has been suggested 107 that phyllocladene may be represented by (CXI) or (CXII) of which the former explains better the degradation to retene. cc-Dihydrophyllocladene produced along with the ,&isomer by the catalytic hydrogenation of phyllocladene is identical with iosene obtained from lignites.lo8 z'soPhyiiocIadene is pro babiy the optical' antipode of the di~erpene mirene isolated by J.R. Hosking and W. F. Short log from the leaf oil of Podocarpus ferrugineus (the &liro tree). This tetracyclic mono-unsaturated diterpene C20H32 has been isolated from various essential oils.ll0 It gives a monohydro- chloride which with potassium acetate affords 6-podocarprene. cc- and 6-Podocarprenes are probably related in the same way as phyllocladene and isophyllocladene. The diterpene kaurene isolated by J. R. Hosking ll1 from the leaf oil of the Kauri pine (Agathis australis) is probably an artefact formed by the action of heat or metallic sodium on cc-podocarprene which is the substance isolated from the oil under mild conditions.112 This tricyclic diterpene C20H32 isolated from the essential Phyllocladene and isophyllocladene.cc- Podocarprene. Rimuene. lo3 L. Ruzicka and M. Stoll Helw. Chirn. Acta 1924 '7 271. lo4B. H. Goudie J . Soc. Chem. I n d . 1923 42 3 5 7 ~ ; H. A. A. Aitken ibid. 1928 4'7 2 2 3 ~ ; W. J. Blackie ibid. 1929 48 3 5 7 ~ ; 1930 49 2 6 ~ ; L. H. Briggs J. 1937 79 ; compare C. W. Brandt New Zealand J . Sci. Tech. 1938 20 8. 1O5 K. Nishida and H. Uada J . Agric. Chem. Soc. Japan 1935 11 489; 1936 12 308; H. Uoda J . Dept. Aqric. Kyushu Imp. Univ. Japan 1937 5 117. loSL. H. Briggs and M. D. Sutherland J . Org. Chew&. 1948 13 4. lo' C. W. Brandt Zoc. cit. ref. (104). lo8 L. H. Briggs J . 1937 1035. log Rec. Trav. chim. 1928 47 834 ; J. R. Hosking ibid. 1930 49 1036 ; compare J. Kawamura Bull. Imp. Forestry Exp.Sta. Tokyo 1931 No. 31 93. 110 K. Nishida and H. Uoda J . Agric. Chem. SOC. Japan 1931,7 157 ; J. Kawamura Zoc cit. ; L. H. Briggs and R. W. Cawley J . 1948 1888. " ' R e c . Trav. chirn. 1928 47 578; 1930 49 1036. ll2 L. H. Briggs and R. W. Cuwley Eoc. cit. ref. (110). 60 QUARTERLY REVlEWS oil of the Rimn tree (Dacrydium cupressinum) 113 and as totarene from that of the Totara tree (Podocarpus totcar@,l14 gives pimanthrene on dehydro- genation and is isomerised to isophyllocladene on digestion with formic acid.lo7 It contains a methylene group and a further unidentified olefinic linkage. Miscellaneous Diterpenoids.-FichteEite. Although fichtelite is not strictly a diterpenoid it is very closely related to abietic acid and so may be considered here. It was first isolated by C.Bromeis 115 from the decayed wood of conifers in which it owes its presence to the decomposition of resin acids under anaerobic conditions. Although this saturated hydrocarbon was the subject of numerous investigations,ll6 it was not until L. Ruzicka F. Balas and H. Schinz 117 had shown that it afforded retene on dehydro- genation with sulphur that real progress could be made with its formulation. Subsequently L. Ruzicka and H. Waldmann 118 found by quantitative dehydrogenation with palladised charcoal that its (previously disputed) formula must be C19H34 and this was confirmed by X-ray analysis.119 In view of the relationship of fichtelite to abietic acid and to retene Ruzicka and Waldmann suggested that it is most probably represented by (CXIII). Marrubiin. The diterpenoid lactone marrubiin C,,H,804 which constitutes the bitter principle of the horehound (&?arrubium vuZgare L.) although known for 60 many years was not isolated in a state of purity until 1932.120 by various workers 121 and some progress has been made (~~111.) with the elucidation of its structure.It contains two ethylenic linkages and is bicyclic giving 1 5 &trimethyl- naphthalene (LXI) on dehydrogenation. Two of the oxygen atoms are present as a lactone ring one as a tertiary hydroxyl group and the fourth probably as an oxide ring. It is possibly related therefore to the 1 7 8-trimethylphenanthrene group of diterpenoids. Stereochemistry of the Diterpenoib.-Some progress has aheady been made in our knowledge of the stereochemistry of the diterpenoids and it is possible t o present a tentative scheme covering the more important centres in those compouncls of established structure.,),- I The chemistry of marrubiin has been investigated 1 113F. H. McDowall and H. J. Finlay J . SOC. Chem. Id. 1926 44 4 2 ~ ; M. S. 114 G. B. Beath ibid. 1933 52 3 3 8 ~ ; comparo H. A. A. Aitken ibid. 1929 48 115 Animlert 1841 37 304 ; compare J. B. Trommsdorff ibid. 1837 21 126. 116 Inter al. T. E. Clark ibid. 1857 103 236 ; C. Hell Ber. 1889 22 498 ; E. Bamberger ibid. p. 635 ; C. Liebermam and L. Spiegel ibid. p. 779 ; L. Spiegel ibid. p. 3369; E. Bamberger and L. Strasser ibid. p. 3361. Carrie ibid. 1832 51 3 6 7 ~ . 34411. 117Helv. Chim. Acta 1923 6 692. l1*1bid. 1935 18 611. 119 D. Crowfoot J . 1938 1241. lZoL. J. Mercier and F. Mercier Conzpt. rend. 1932 195 1102. lz1 H.M. Gordin J . Amer. Chem. SOC. 1908 30 265 ; A. Lawson and E. D. Eustice J. 1939 587 ; F. Hollis J. H. Richards and A. Robertson Nature 1939 143 604. BAaTON THE CHEMISTRY OF THE DITERPENOIDS 61 It was mentioned on pp 40 46 that vigorous oxidation of abietic (VI ; R = H) and dextropimaric acids gives a C1,H1606 tricarboxylic acid derived from ring A. This acid is optically inactive and must therefore possess a plane of symmetry i.e. the 1- and the 3-carboxyl group must be in the cis-relationship to each other. The carboxyl attached a t position 2 has recently been shown by D. H. R. Barton and G. A. Schmeidler,122 from a study of dissociation-constant data to be related in the trans-sense to the other two carboxyl groups so that the A/C ring fusion in abietic acid and related acids must also be trans.* The remaining asymmetric centre in abietic acid a t C13 (see VI) is probably in the trans-relationship to the C, methyl group.This is so because it would be anticipated that treatment with acidic reagents (as in the preparation of abietic A acid) would provide a mechanism for the (' A/ '-$ at this centre. There is support €or this \ ;B\ ,Q Ro& assumption of the more stable configuration A v \/ \, argument in the work of W. Sandermann,lz4 13 who prepared an isomer of abietic acid by lo * Ti/ pyrolysis of the levopimaric acid malcic \ A- W I (VI.) anhydride adduct and from nbietic acid dihydrobromide. He called this isomer iao- abietic acid and showed that it was possibly epimeric with abietic acid a t the C13 position. On treatment with hydrogen chloride it was rearranged to abietic acid.From the strong lzevorotation of abietic and levopimaric acids it is probable that they have the same configuration at C13. neoAbietic acid which is strongly dextrorotatory (p. 44) must by this reasoning have the opposite configuration to abietic acid a t C,,.94 Since manool has been related directly to dehydroabietic acid (p. 55) it must have the same configurations as abietic acid at C, and C12. This also establishes the configurations of manoyl oxide (p. 54) ketomanoyl oxide (p. 54) a,nd sclareol (p. 53) a t these centres. Very recently,f25 L. Ruzicka R. Zwicky and 0. Jeger have shown that agathenedicarboxylic acid has the same ring fusion as for rings A/C of abietic acid. When the agathenedicarboxylic acid derivative (LXV) (p. 49) was dehydrogenated by the bromosuccinimide method it gave the correspond- ing dehydro-derivative (CXIV) converted by standard methods into the J.1945 1197. l P 3 D . II. R. Barton Cheit~. und Id. 1948 638. lZ4Ber. 1943 76 1257 1261 135 HeEv. Chi???,. Actu 1948 31 2143 ; the author is indebted to Dr. 0. Jeger for a copy of this paper before its publication. * Treatment of the various diliyciroabietic acids with strongly acid rcagents gives an isomeric lactoae C20H3209 m.p. 130-131° [alD ca. - 2' (in alcohol). This substance is usually considered t o be lactonised at the CIS position. Its formation in this way has been taken to support a cis A/C ring fusion since it caiinot possibly be built up on models if the A/C fusion is trans. The accepted formula for this lactone must be in error and it has been suggested elsewhere lZ3 that its formation involves a migration of the C, methyl group compa,rable to tkat taking place in the genesis of Westphalen's diol .62 QUARTERLY REVIEWS partly aromatic hydrocarbon (CXV) which was obtained also from the manool derivative (XCI) (p. 55) by reaction with methylmagnesium iodide to give the diene (CXVI) and dehydrogenation of the latter with bromo- succinimide. These experiments also provide an unambiguous proof of the point of attachment of t,he C,,-methyl group in agathenedicarboxylic acid. Both the agathenedicarboxylic acid derivative (LXV) and the manool derivative (CXVI) have strong lzvorotations similar to that shown by abietic acid. For this reason t'hey probably have the same configuration a t C, as in abietic acid.Assuming that inversion at this centre has not occurred during their preparation this may be taken as evidence for the same configuration at C, in agathenedicarboxylic acid manool manoyl oxide lsetomanoyl oxide and sclareol as in abietic acid. These conclusions on stereochemistry are summarised in the table. (LXV.) (CXIV. ) Abietic acid . . . . . isoRbietic acid . . . . neoAbietic acid . . . . Dextropimnric acid. . . Levopimaric acid . . . Podocarpic acid. . . . Agathenedicarboxylic acid. Manool . . . . . . Manoyl oxide . . . . Sclareol . . . . . . Ketomanoyl oxide . . . Ferriiginol . . . . . (XCI.) ! (CXV.) (CXVI.) C02H at C arid H at C,,. cis cis C i S Relationship between H at C, and Me at CL2. trans trans trans trans truns tram trans trans tram trans trans trans Me at C, and 11 at C13.trans cis ? cis ? > trans trans ? trans ? trans. ? trans ? tram ? - - Relationships between Di- and Tri-terpenoids.-This is a field of the greatest importance for t,he find clarification of the structures of the BARTON THE CHEMISTRY OF THE DITERPENOIDS 63 triterpenoids. Important advances can be expected therein in the near future. The formulation of rings D and E of ambrein (CXVII) 126 has been elegantly confirmed by the experiments of L. Ruzicka 0. Diirst and 0. Jeger.127 When ambrein is oxidised it affords7l2* amongst other products a saturated lactone (CXVIII) which can be degraded through the cor- responding saturated acid (CXIX) t o an acid identical with that (LXXXIX) obtained previously from inanool. These cxperiments also establish that the ring fusion between rings D and E (CXVIII.) in aibrein is trans (see above).(CXIX .) (LXXXIX. ) 1 E I \/ /\ (CXX.) (CXXI.) /y -+ C0,H C0,Me C0,bIe (CXXIV. ) (CXXIII . ) (CXXII.) A similar important correlation has now been established between oleanolic acid probably (CXX) and manool through a common degradation product of the former and of a m b r e i ~ ~ . l ~ ~ Pyrolysis of the keto-lactone (CXXI) obtained from oleanolic acid aEordec1 amongst other products las E. Leclerer and D. Morcier Exprientia 1917 3 18s ; 0. Jeger 0. Diirst and 127 Ibid. 353. lZ8 L. Ruzicka and F. Lardon ibid. 1946 29 912 ; E. Ledercr F. Marx D. Mercior and G. Perot ibid. 1354. 129 L. Ruzicka H. Gutmann 0. Jcger and E. Lederer iGid. 1948 31 1746 ; t h o author is indebted to Dr. 0. Joger for a copy of this paper before its publication.L. Ruzicka Helv. C h i m Acta 1947 30 1859. 64 QUARTERLY REVIEWS a keto-ester (CXXII) reduced by the Wolff-Kishner method to the saturated acid (CXXIII). The latter was also prepared from ambrein in the following way. Oxidation of ambrein with potassium permanganate gave amongst other products the saturated hydroxy-acid (CXXIV) which by dehydration and then hydrogenation was converted into (CXXIII). These experiments show that the A/B ring fusion in oleanolic acid must be trans in agreement with the X-ray data of G. Giacornello.l30* The Reviewer wishes to express his indebtedness to Sir John Simonsen F.R.S. for many valuable discussions and t o Mr. C. J. W. Brooks for help with the manuscript. 13* Gazzetta 1935 68 363 ; compare L. Ruxicka and H. Gubser Helv.Chim. Acta 1945 28 1054. * An account of the chemistry of the minor diterpenoids cryptomerene and cupres- sene will be found e1sewhe1-e.~ Cafestol (cafesterol) and kahweol have not been considered in the present Review although they are possibly diterpenoid in character.g4

ISSN:0009-2681    

DOI:10.1039/QR9490300036

出版商:RSC    

年代:1949

数据来源: RSC

摘要:

TRANSITIONS IN SOLIDS AND LIQUIDS By L. A. K. STAVELEY M.A. (FELLOW OF NEW COLLEGE OXFORD AND UNIVERSITY DEMOXSTRATOR IN CHEMISTRY) IT has long been known that many substances exist in more than one solid form such that a t constant pressure one form changes into another a t a constant temperature just as a pure substance passes isothermally from the solid to the liquid statte a t the melting point. The thermodynamic descrip- tion of such transitions is simple. At the transition point the Gibbs free energies G of equal masses of each of the two solid forms are equal the free- energy curves (at constant pressure) intersecting as shown in Fig. 1 (a). The change from the low-temperature to the high-temperature form takes place with the‘ absorption of latent heat and so is accompanied by a sudden entropy increase and there is also an abrupt volume change.The effect of pressure on the transi- tion temperature is governed by the Clapeyron-Clausius equation. dp/dl’ = AS/(VI - VII) . ( 1 ) There also exist transitions in pure solid substances which do not take place sharply but over a range of tem- perature even though the major part of the change whatever it may be is 2 FIG. 1 often concentrated into a small tern- T h e elutions ship between free energy (a) (b) second and ( c ) third order. perature region. Such transitions are and tenLPerature in transitions now known to occur in substances of widely different chemical types. They are found for example in ammonium salts in condensed gases such as methane and hydrogen bromide and in alloys. They also include Curie-point phenomena in ferromagnetic materials and the analogous effects which take place in ‘‘ Seignette-electric ” sub- substances.In addition the one known transition in a purely liquid sJrstem that between the two forms of liquid helium is of this kind. Few generalisations can be made about these transitions but they are alike in one respect of great practical and theoretical importance narnely that they are all accompanied by an anomaly in the specific heat. As the low-tem- perature form ofthe substance is heated the heat capacity cp starts to become greater t8hm would be expected from its previous trend with temperature. The rise becomes more and more rapid until a maximum value is reached 65 E 66 QUARTERLY REVIEWS (Fig. 2). Sometimes the subsequent fa,ll is continuous sometimes apparently discontinuous though even if the drop is discontinuous the " normal " curve is usually not resumed a t once.Just above the temperature a t which it reaches its maximum the heat capacity lies slightly above the extrapolated normal curve. This behaviour is described as anomalous since it is not possible for the normal heat capacity due to the progressive excitation of the lattice vibrations and of the internal vibrations in molecules or ions to decrease with rising temperature.l The coefficient of expansion in a gradual transition likewise shows an anomaly similar to that in the specific heat except that it sometimes takes the form of abnormally small ( i e . negative) values in the transition region. TPK.) FIG. 2 The variation with temperature of c (ref. 36) and c, (ref.25) in the gradual transition in ammonium chloride. There is however considerable variability in these anomalies from one substance to another. Sometimes the heat capacity a t its maximum is only a few calories above the normal (extrapolated) curve sometimes it reaches N 100 cals./mole or even immeasurably high values. The observable range of the anomaly may be restricted to a few degrees and its main part t o a fraction of a degree only ; or it may spread over more than loo" parti- cularly in transitions in alloys. In calorimetric and dilatometric studies the transition temperature is taken to be that a t which cp reaches its maximum value and the coefficient of expansion its maximum or minimum value as the case may be. R. H. Fowier and E. A. Guggenheim '' Statistical Thermodynamics " (C.U.P.1939) p. 147. STAVELEY TRANSITIONS IN SOLIDS AND LIQUIDS 67 The thermodynamic description of these gradual transitions was first attempted by P. Ehrenfest.2 At a sharp transition we have two physically distinct phases in equilibrium with eqiaal free energies G and it follows from the relations that there is a sudden alteration in entropy and volume. Ehrenfest con- sidered what the thermodynamic consequences would be if at a transition there is equality of the free energies of the two forms and of their first differential coefficients as well but now a discontinuity in their second differential coefficients. (The choice of the rather ambiguous word ‘‘ form ” in the last sentence is deliberate. We shall see that there are cogent reasons for avoiding the word “ phase ” in dealing with gradual transitions.) At constant pressure the relationship between the free energies of the two forms will then be as shown in Fig.1 (b). At a certain temperature the curves will touch with the same slope but with different curvatures. At this temperature from the relations there will be a discontinuity in specific heat and coefficient of expansion. If now a(AG)/aT and a(AG)/i3p (where AG = GIr - GI) are to remain zero for changes in T and p we have the equations (aC/aT)p = - S (aG/ap)T = V . (2) aw/aT= = - c~/T aw/arrap = av/aT . * (3) and whence from (3) and the additional relation a2G/ap2 = aV/ap we have Such transitions in which there is a discontinuity in the second differential coefficients of C can be called second-order transitions in contrast to sharp transitions which are of the first order.E. Justi and M. voii Lsue 3 raised doubts about the possibility of the existence of second-order transitions pointing out that one form would always have the lower free energy [I in Fig. 1 ( b ) ] and hence that the transition I -+ II could never be observed. As the simplest way out of this apparent difficulty they suggested that there is a sudden change not in the second but in the third differential coefficients of G so that a t constant pressure the free energy relationship would be as shown in Fig. 1 ( c ) . There would then be no discontinuity in ep or in cc (the coefficient of expansion) but the curves of these quantities plotted against temperature would show a sudden alteration in slope a t the transition temperature. Justi and von Laue’s argument has however been criticised on the grounds that it is not permissible to regard the two forms of the substance separated by the anomaly as two phases with a conceivable existence on both sides of the transition point ; in other words 2Proc.Acad. Xci. Amsterdam 1933 36 153. a Sitzungsber. Akad. Berlin 1934 237. 68 QUARTERLY REVIEWS that the two forms are such that one passes continuously into the other so that extrapolation of either beyond the transition temperature is meaningless. 4 The equations (4) can in principle be subjected to experimental test the first of them being the more convenient. Unfortunately the necessary data are only available for a few substances and moreover it is difficult in any case to obtain accurate figures for the sudden changes in heat capacity and coefficient of expansion at the transition temperature.The test has however been applied t o the transition in liquid helium. Here within the limits imposed by existing experimental technique there does appear to be a discontinuous drop in cp (of 1-9 cals./mole) at the temperature (2.19" K.) a t which the lom-temperature form of liquid helium (11) finally passes into the high-temperature form I. According to W. H. Keesom and A. P. Kee~oni,~ this fall in c certainly occurs within 0.002" and probably within 0.0002". By using experimental figures for the rate of change of the transition point with pressure (= dp/dT) and for the coefficient of expansion of liquid helium I W. H. Keesom calculated from equation (4) a value for the coefficient of expansion of helium I1 a t the transition temperature which was in very fair agreement with the experimental figure.The Ehrenfest equation has also been applied to the gradual transitions in methane 7 and amnionium but there are doubts about its applicability to either of these. For methane there is considerable uncertainty about the value of Ac at the transition,* and in fact A. Eucken and E. Bartholom6 con- sidered that the possibility of the drop in cp being bontinuous could not be excluded. For ammonium chloride as we shall see there is evidence that the transition from the low- to the high-temperature form finally reaches completion isothermally or atl least in such a small temperature range as to make an accurate evaluation of Ac and Am impossible. In some gradual tranfiitions there definitely does not appear to be an abrupt fall in the heat capacity ELS for example in ferromagnetic elements in the neighbourhood of the Curie point.At this temperature the heat capacity reaches a somewhat pointed maximum and then declines con- tinuously to normal values. This behaviour is consistent with that required of a third-order transition and specific heat and coefficient of expansion anomalies in ferromagnetic elements have in fact been treated thermo- dynamically as belonging to this class.l* The first applications of statistical mechanics to gradual transitions dealt with the so-called order-disorder phenomena in certain alloys,t of J. E. Mayor and S. F. Streeter J. Claena. Physics 1939 7 1019 ; W. H. Iieesom Proc. Acad. Sci. Atnsterdam 1933 36 147. K. CIusius and A. Perliclr 2.physikal. Chena. 1933 B 24 313. Ciiftingen Nachr. Math.-Phys. K1. 11 1936 2 51. " Helium " (Elsevier 1942) Chap. 5. Physica 1935 2 557. 8E. 0. Hall Physical Rev. 1947 71 916. lo E. F. Lype Physicat Reu. 1346 69 653. ' Sce ref. (9) p. 5.5. t See F. C. Nix and ?V. Schockley Rev. Mod. Plysics 1938 10 1 for an excellent review of this sithject. STAVELEY TRANSITIONS I N SOLIDS AND LIQUIDS 69 which /?-brass (CuZn) is a simple example. The nrcture of the transition has been established by X-ray studies. In /I-brass both above and below the transition the atoms are situated a t the points of a body-centred cubic lattice. At low temperatures the structure can be regarded zs consisting of two interpenetrating simple cubic lattices one of copper atoms the other of zinc so that each copper atom is surrounded by eight zinc atoms and vice versa.Above the transition however there is no discrimination on the part of the atoms as to which lattice points they occupy so that on the average either kind of atom has four coppers and four zincs as nearest neighbours. Certain planes in the high-temperature disordered structure resolve themselves in the low-temperature ordered form into planes alter- nately consisting of each kind of atom only with different scattering powers so that X-rays are diffracted from adjacent layers of this kind with equal intensities at high temperatures and with unequal intensities a t low tem- peratures. Diffraction from these planes at low temperatures produces lines in the diffraction pattern (" superlattice lines) due to the incomplete cancellation of out-of-phase beams which are absent from the diffraction pattern of the high-temperature form.This evidence shows that it is the ordered form in which the potential energy is least but thermal agitation tends increasingly to produce the disordered state and the degree of order at any given temperature depends on a balance between these opposing factors. The definition of the degree of order s in the treatment of the problem given by W. L. Bragg and E. J. Williams 11 may be illustrated as follows. To produce p-brass we could take a body-centred cubic lattice with each of its n lattice points occupied by a copper atom and then replace half of them by zinc atoms. To obtain the completely ordered alloy the replace- ments would have to be made a t certain definite lattice points only (" correct " positions) n/Z in number.If now when the substitutions are made the average chance that a zinc atom is placed at a '' correct " position is p then s is defined as (the actual value of p ) - (value of p for complete disorder) (value of p for complete order) - (value of p for complete disorder) _______ = ( p - $)/(1 - 3) = 2(p - $) Changing the places of a copper and a zinc atom in the completely ordered alloy will involve an increase of potential energy W, but for the completely disordered alloy no alteration in potential energy will accompany Ghe interchange. In any intermediate state $he increase in potentiad energy JV will lie between 0 and Wo and will be a function of s. In Bragg and Williams's treatment W was taken to be a lingar function of s. But there will clearly be another relation involving s W and T since in a sense the transition is analogous to a chemical reaction with s playing the part of an equilibrium constant and W that of a heat of reaction (with the peculiarity that the " heat of reaction '' varies with the extent to which the reaction has taken place).This second Hence s = 1 or 0 for complete order or disorder respectively. We now come to a most important point. 11 Proc. Roy. SOC. 1934 A 145. 609 ; 1935 A 151 540. 70 QUARTERLY REVIEWS equation can be derived by the methods of statistical mechanics and fkom the two equations involving W 2nd s the equilibrium value of the degree of order at any temperature T can be determined. It is found that s falls more and more rapidly with increasing temperature until it becomes zero a t a temperature T,.(For alloys of the type AB such as CuZn the fall to zero is continuous. For some systems of the type AB, such as CU~AU s after a continuous fall drops ubmptZy to 0 at T, so that here the final disappear- ance of order is accompanied by the absorption of latent heat.) The cal- culated values of the anomalous specific heat below T are of the right order of magnitude. The theory accounts successfully for the essential features of the transition except that it predicts that the system would have a normal specific heat immediately Tc is passed whereas in fact for a short range above T the cp values are still slightly greater than normal. The reason for this is that the degree of order as defined above is an average quantity which relates t o the crystal as a whole.At all temperatures however there is a tendency for the immediate environment of a given atom to be such that the potential energy of this atom and its neighbours is a minimum and the local order to which this tendency gives rise will in virtue of its contributory potential-energy term manifest itself in an addition to the specific heat decreasing in value as T increases. N. Bethe 1 2 and R. Peierls l3 have presented treatments of order-disorder transitions in alloys in which the degree of order CT is defined with reference to an atom and its nearest neighbours only ; CT is thus a measure of the short-range order which unlike s does not become zero at Tc. From this starting point the slightly anomalous specific heat above T can be accounted for quanbitatively. There is some similarity between Curie-point phenomena in ferro- magnetic substances and transitions in alloys.The atoms in a ferro- magnetic substance are elementary magnets with a preference for a common orientation which at sufficiently low temperatures results in a state of permanent magnetisation. As the temperature rises thermal agitation tends increasingly to overcome this common orientation. The disappearance of permanent magnetisation at the Curie point is accompanied by a maximum in the specific heat. Of all gradual transitions those occurring in molecular and ionic solids have probably the greatest interest for the chemist. The majority take place below room temperature and the discovery of many of them has been a consequence of systematic low-temperature calorimetry. Usually the compound contains hydrogen in its molecule or one of its ions and it may possess two or even three such transitions.I n finer points of detail these gradual transitions show great sensitivity to the chemical nature of the compound in which they occur. Even isotopic replacement can cause qualitative changes. The first to be definitely discovered was that in ammonium chloride by F. Simon,l* R. Ewald l5 having previously observed that the heat capacity of this substance below room temperature was laproc. Roy. XOC. 1935 A 150 552. =&Ann. Phyaik 1922 68 241. l S I b i d . 1936 A 154 207. '"bid. 1914 44 1213. STAVELEY TRANSITIONS IN SOLIDS AND LIQUIDS 71 anomalous. They have since been found to exist in numerous ammonium and other salts and in many condensed gases and organic compounds.A considerable stimulus to their experimental and theoretical investigation resulted from L. Pauling’s suggestion 16 that they might mark the onset of molecular or ionic rotation in the crystal lattice. The possibility of such rotation seems to have been first considered by P. Simon and C. von Simson l7 to account for the cubical symmetry of the high-temperature form of hydrogen chloride. Pauling applied the Schrodinger equation to a molecule the potential energy of which was assumed to be a periodic function of its orientation. At low temperatures the molecule executes torsional oscilla- tions. At high temperatures it rotates non-uniformly a t first but more and more smoothly as the temperature rises. The change from the first type of motion to the second is favoured by a small moment of inertia of the molecule or ion and by a low barrier separating two minima in the potential energy.Pauling concluded that molecules like the hydrogen halides and methane should be capable of rotation in the crystal lattice a t temperatures below the melting point whereas this would not be true of a molecule like iodine with its much larger moment of inertia. He suggested that in solid hydrogen halides the change from torsional oscillation to rotation takes place a t a transition and predicted that at these transitions the dielectric constant would show a marked increase. This prediction has since been verified,l* and similar effects observed a t transitions in many other _polar substances.l9 This association of transitions in molecular and ionic solids with the change from librational to rotational movement undoubtedly provides a simple explanation of many of the facts.20 In the first place we can easily understand why so many of these transitions are gradual.At low tempera- tures the molecules are constrained to undergo torsional oscillations by the directed nonspherical field of force acting on them. If a molecule com- mences to rotate however the resulting increase in symmetry in its own field of force weakens its orientating influence on its neighbours and makes their rotation an easier process. In other words we have here as in order- disorder transitions in alloys a change which becomes progressively less exacting in its energy requirements as it proceeds. Like the atomic re- arrangements in alloys it will be a co-operative phenomenon giving rise to abnormal physical properties over a range of temperature.In sharp transitions where there is evidence that molecular rotation sets in a t the transition point it may be that this does not occur a t all a t lower tempera- tures and that the conditions which make it possible are created by the change in crystal structure a t the transition. But it is also possible that just below the transition point a few molecules or ions begin to rofate with 16 Physical Rev. 1930 36 430. l8 ( a ) R. M. Cone G. H. Dcnnison and J. D. Kemp J . Amer. Chem. SOC. 1931 53, Is C. P. Smyth Chem. Reviews 1936 19 329 ; Faraday Society Discussion 013 ,OA. Eucken 2. Elektrochem. 1939 45 126. 2. Physik 1924 21 168. 1278; (b) C. P. Smyth and C. S. Hitchcock ibid. 1933 55 1830. Dielectrics 1946 175.72 QUARTERLY REVIEWS such an effect that the lattice is compelled to alter radically before the incipient rotation has given rise t o a detectable anomaly in such properties as specific heat and coefficient of expansion. Later we shall see that i t is unwise to regard sharp and gradual transitions as being funda8mentnlly different since some appear to have the character of both in that they commence gradually but probably reach completion isothermally. Evidence in support of Pauling's theory comes from a consideration of the temperatures a t which transitions occur in substances of different chemical types. The temperatures at which cp reaches its maximum in the gradual transitions in methane hydrogen bromide ammonium chloride and sodium nitrate are 20.42" 59-75" 242.7" and 548" K.respectively. (Hydrogen bromide has two more transitions some 25 " higher.) In methane the intermolecular action is due almost entirely t o weak London dispersion forces but in hydrogen bromide there are stronger orientating forces between the permanent dipoles. In amrrionium chloride and sodium nitrate there are still more powerful interionic effects. The nitrate ion has a much larger moment of inertia than the ammonium ion. It is therefore readily under- standable that on passing along these four substances there should be an increase in the temperatures of the transitions if these are due to the com- mencement of rotation of the molecules of the first two and the cations and anions of the third arid fourth. Two o6her interesting series are provided by water hydrogen gulphide and hydrogen selenide and ammonia phos- phjne and arsine.I n each of these groups the first substance (with the most strongly polar molecule) only exists in one solid form a t ordinary pressures. I n the other two compounds of each series the lowest transition occurs in that which has the smallest dipole moment. For gradual transitions which are seldom accompanied by more than a slight change in crystal structure the entropy change rarely exceeds 2 e.u. (cals./mole/o) whereas for a sharp transition i t is often greater. A sub- stance possessing either kind of transition however invariably has a lower entropy of fusion than a substance which is chemically similar but non- polymorphic. Thus the entropy change at the sharp transition (at 225.35" K.) in carbon tetrachloride 21 is 4.86 e.u.and that on melting (at 250.3" K.) is 2.4 e.u. while the entropy of fusion of silicon tetrachloride 22 (which has no transition) is 9.1 e.u. Sonietimes the entropy of transition is so much larger than that of fusion that the high-temperature form of the solid must already in a sense be very " liquid-like ". For cyclohe~anol,~~ for example the entropy increases by 7-44 e.u. at the transition at 263-5" K. and by only 1.37 e.u. at the melting point (297.0" K.). This state of affairs is quite comprehensible if a t the transition the molecules acquire the orientational freedom which otherwise is only gained when the solid melts. Likewise if the dielectric constant increases considerably a t a transition in a polar substance its further change on melting is usually only small.Nevertheless it is wrong to conclude that uZZ gradual tramitions in 21 J. I?. G. Hicks J. G . Hooky and C. C. Stephenson J . Amer. CJ2t.m. Soc. 1944 2 a W. M. Latimer ibid. 1922 44 90. 66 1064. 33 R. K. JCelley ibid. 1920 51 1400. STAVELEY TRANSITIONS IN SOLIDS AND LIQUIDS 73 molecular and ionic solids are associated with the change from torfiional oscillation to comparatively €ree rotation of molecules or ions even about one axis only. We shall see that experimental evidence while indicating that in some lattices these particles may have almost the same rotational freedom that they enjoy in the gaseous state can for other solids only be reconciled with the persistence of librational movement both above and below the transition so that here the increase in disorder is to be attributed not to the change from libration t o rotation but from libration about ordered axes to libration about disordered axes.Consequently the indiscriminate application of the term “ rotational transition ” to these gradual changes in the kind of solid we are discussing is not justifiable just as the expression “ second-order transition ” likewise takes too much for granted. Less objectionable terms are “ lambda-point ” and “ ammonium chloride-type transition ”. The first of these was coined by P. Ehrenfest and was sug- gested by the shape of the cp anomaly in l i q ~ i d helium. The first attempt to account quantitatively for specific heat and coefficient of expansion anomalies assumed to be due to incipient molecular rotation in crystal lattices was made by R. H. Fowler.24 His treatment was similar to that which Bmgg and Williams had applied to order-disorder transitions in alloys.A molecale wits msumed to be in a potential field of - ‘clr cos 8. An order parameter s was introduced which was regarded aR representing the average degree of non-rotation of the molecules and for the all-important dependence of JV on s Fowler assumed that they were related by the equation W = Was. The calculated values of the heat capacity refer of course to constant volume and cannot strictly be com- pared with directly determined cp values. For ammonium chloride however experimental values of cv are now available 25 which show that the anomalous rise in cv is much less pronounced than that in cp (see Fig. 21 and indeed is much what would be expected from Fowler’s theory.Actual specific-heat anomalies are usually concentrated into a smaller temperaixre range than the theory predicts for which the neglect of the effect which any volume change accompanying the transition may have on the potential energy is probably partly responsible. 2 8 T 2 7 Further theoretical work in this field has been carried out by J. G. Kirkwood 27 and K. Schafer,28 both of whom have treated the transition as involving a change from a preferred to a random molecular orientation rather than from non-rotation to rotation. An essential point in Schafer’s theory is that the unit to which statistical considerations are applied is not the whole crystal but a domain consisting of comparatively few molecules (perhaps - lOOO) so that the interaction energy of the molecules in it is a function of the size of the domain.One feature of these transitions has yet to be mentioned namely the hysteresis which often (though by no means invariably) accompanies them. 24 Proc. Roy. Soc. 1935 A 149 1. 25 A. W. Lawson Physical Rev. 1940 57 417. 26 0. B. Rice J . Chern. Physics 1037 5 492 ; cf. R. Eisenschitz Proc. Roy. Icoc. 2 7 / b i d . 1940 8 205. 2 8 Z . physikal. Cliem. 1939 B 44 127. 1938 A 168 645 ; H. Bethe and J. G. Kirkwood J . Chen~. Physics 1939 7 578. 71 QUARTERLY REVIEWS The temperature of a transition showing hysteresis is higher when approached from the low-temperature side than that at which the reverse change occurs on cooling (Fig. 3). Some very careful investigations of this phenomenon have been made from which i t appears that when it exists it shows no sign of vanishing in a reasonable period of time and that it is unaffected by the measures which normally assist the establishment of equilibriuni.(Thus the hysteresis in the transition in sulphur hexafluoride is not altered by the presence of liquid carbon tetrafluoride in which it is somewha,t soluble.) 29 Although it is by no means fully understood it is not unlikely that it is connected with the mosaic structure of the crystal. Schafer 28 has applied his theory to the problem and suggests thaf the ordered domains first formed on cooling the solid through the transition will be smaller than the larger ones produced laber on and hence have dizerent properties and a different transition temperature. Another view is that the volume changes occurring in small regions of the crystal cause strains to be set up and that the hysteresis arises from t'he effect of the resulting pressure on the transition temperature.3O Different forms of a solid a,re designated as I 11 111 ctc. I being the form stable between the melting point and the highest transition temperature I1 that existing between this and the next lower transition temperature and so on. Reference will be made to the recently developed nuclear magnetic resonance method of deciding whether or no molecules or ions rotate in crystal lattices which has been applied to compounds containing hydrogen atoms.31 This depends on the fact that the effect of an applied magnetic field on the spins of the protons is to cause them t'o adopt parallel or anti-parallel orientations with respect to the field. The energy diEerence between the two orientations varies with the Geld strength and for the strengths employed corresponds to a quantum of radiation of frequency of the order of ten metres.I n the presence of the magnetic field the substance absorbs radiation of the correct frequency but if the protons are present in a lattice in molecules or ions which are not rotating there will exist in the crystal an inhomogeneous magnetic field which superimposed on the applied field will result in the absorption of radiation over a frequency range. If the molecules or ions rotate with a frequency greater than that of the radiation the internal field will be effectively homogeneous and the range of frequencies absorbed much smaller. The change from libration to rotation will therefore be manifested by a decrease in the width of the absorption line.Ammonium Halides.-In Table I are given the absolute temperatures entropy changes A 8 (in cals./mole/") and volume changes AV (in c.c./mole) for the transitions in light and heavy ammonium halides. The entry in the column headed " f1 " gives the width of the hysteresis loop in degrees. We shall now consider some typical transitions in detail. 23A. Eucken and E. Schrocler Gotlingen Nmhr. Math.-Phys. K1. 11 1938 3 65. 30 F. C . Frank and K. TVirtz NuturuGss. 1938 42 657 ; P. Dinichert Helv. Physica 31 F. Bitter N. L. Alpert H. L. Poss C. G. Lehr and S. T. Lin Physical Rev. Acta 1944 1'7 389. 1947 71 738. STAVELEY TRANSlTIONS IN SOLIDS AND LIQUIDS 75 '' No " means that the transition does not show hysteresis. The reference numbers indicate the murce of the information in $he column above them.NH,Cl . ND,Cl . NH,Br. ND,Br . NH,I ND,I . Ref. . TABLE I T OK. 457 448 414 405 258 32 - TIT + 11. 1 IV -f 111. I AV + 5.26 - + 6.34 + 8.14 34 - - T OK. 242.7 249.3 234.4 215 233 229 32,35 A S 0.82 0.34 0.30 36 - - - AV N + 0.16 - + 0.13 N - 0.06 N - 0.17 - - 0.1 N - 0.1 35 a ,-- 0.27 NO - 0.06 ,- 0.15 N O NO 35 T OK. All of the transitions 111 + I1 and IV + IT1 are gradual. Sometimes the anomalies in specific heat and coefficient of expansion extend for as much as 30" or 40". The I and I1 forms of these salts have face-centred and body- centred cubic lattices respectively. II-NH,Cl passes into III-NH,C1 with no fundamental lattice ~hange,~7 3t3 but 111 is piezoelectric 39 and therefore of lower symmetry than 11. The very careful dilaiometric study by A.Smits and C . H. MacGillavry 35 revealcd that a considerable part of the volume change in the I11 + I1 transition occurs within a few hundredths of a degree (see Fig. 3). This important observation suggests that this transition begins gradually in one and the same phase but that eventually it is perhaps completed isothermdly. By contrast thc III + I1 transition in ND,Cl takes place continuously with no sudden volume change and without hysteresis (Fig. 3). III-NH,Br on the other hand is doubly refracting and has a tetragonal structure though only slight displacements of the ions fi-om their positions in the body-centred cubic II-form are 379 Here also much of the anomalous volume change takes phce in an extremely small temperature interval-within 0-Ol" according to A.Smits J. A. A. Ketelaar and G. J. M ~ l l e r . ~ ~ ND,Br provides one of the few examples of a qualitative 3 8 K. Clusius A. Kruis and W. Schanmr 2. anorg. C'hern. 1938 236 24. 33H. Klindhardt Ann. Physik 1927 84 167. 36 A. Smits and C. H. MrzcGillavry 2. physikal. Chem. 1933 A 166 97 (NH,Cl) ; ,4. Smits G. H. Mnller and F. A. Kroger ibid. 1937 B 38 177 (ND,CI) ; A. Smits J. A. A. Ketelaar and G. J. Muller ibid. 1936 A 175 359 (NH,Br) ; 9. Smits D. Tollonaar and F. A. Kroger ibid. 1938 B 41 215 (ND,Br) ; A. Smits and G. J. Muller ibid. 1037 B 36 140 (NH,T) ; A. Smits and D. Tollenaur ibid. 1942 B 52 222 W. Bridgman Proc. Aiizer. Acad. 1916 52 55. tND,I)- 3aF. Simon C. von Simson and M. Ruhemann ibid. 1927 A 129 339. 37 J. A. A. Iietelaar Nature 1934 134 250.38 P. Dinichert Helv. Physica Acta 1942 15 462. 39 A. Hettich 2. physikal. Chenr. 1934 A 16S 333 ; S. Bahrs and J. Engl Z. Physik ao J. Weigle and K. Saini Helv. Physica Ada 1936 9 515. 1937 105 470. 76 QUARTERLY REVIEWS difference between hydrogen and deuterium compounds in tfint8 i t possesses another transition at a stiil lower temperature a t which i t reverts to a body-centred cubic lattice.35 None of the forins of ND,Rr is piczoeleetric,al and as there is nothing to distinguish forms P I and TV Smits has called the cha'nge I11 + IV a retrograde transition and has discussed i t in terms of his theory of allotropy. This transition is accompanied hy an unusually wide hysteresis loop (- 9"). I<. Clusius 4 2 has referred t o some unpublished experiments on mixed crystals of light and heavy ammonium bromide which TPC.) Fro.3 l'he anriation with temperature of the molar volumes of NH&1 and ND,Cl (ref. 35) in the %final stages of th,e gradual transitions in these substances. showed that the supercooling which precedes the formation of IV from 111 increases with the hydrogen content cntil finally the transition can no longer be observed. The I11 = I1 transitions in NH,I and ND,I involve the same structural change as for NH,Br,35s 37 but they are more extended free from hysteresis and continuous throughout. By measuring Young's modulus and the rigidity modulus of compressed rods of ammonium chloride A. W. Lawson 25 obtained values for the isothermal compressibility #? above and through the transition region. He also determined the coefficient of expansion a and using the relation cp - c = Ta2V//3 calculated c (see Fig.2). The anomaly in c is very much less marked than that in cp (never exceeding - 4 cals./mole) and just above the transition c is 18 cals./mole. The 6 cals./mole left after deduction of 12 for the lattice vibrations of the NHf and C1' ions (which at this tem- perature make a classical contribution of R per degree of freedom) is exactly the amount to be expected if each of the ammonium ions executes torsional oscillations in three degrees of freedom whereas their free rotation would contribute 3 cals./mole to c, making a total of 15. This strong evidence against free rotation of the NH,+ ions in form I1 is supported by the nuclear l A . Smits and P. G. Mesrmann 2. plzysiknl. Chem. 1941 B 49 13. r z Z . Natr~rforsch.1946 1 142. STAVELEY TRANSITIONS 1N SOLlYS AND LIQUIDS 77 magnetic resonance method 31 the width of the broad absorption line shows no change in passing through the transition. It would therefore seem that in NH,Cl a t least both above and below the I11 s I1 transition the cations undergo torsional oscillations presumably about ordered axes in I11 and disordered axes in 11. Whether the motion more nearly approaches free rotation in the high-temperature form I remains an open question. In studying the Raman effect in ammonium chloride bromide and iodide a t temperatures down to - 150° A. C. Menzies and H. R. Mills 43 discovered that with the transformation into I11 there appears in the spectrum of the chloride (but not of the other two salts) il line of low frequency (183 cm.-l).This they attributed to asymmetric lattice vibra- tions of the cations with respect to the anions. They suggested that the equilibrium position of an ammonium ion is such that each face of the tetrahedron is perpendicular to a cube diagonal and that the low-tempera- ture form of ammonium chloride is built up by simple translation of an elementary cube. The halogens are then not symmetrically placed with respect to the ammonium ions so that the low-frequency Raman line is accounted for but the asymmetry would vanish if the cations were to undcrgo torsional oscillations of " moderate amplitude ". On the other hand by constructing the lattice from elementary cubes so that the tetrahedra are arranged antisymmetrically a group of eight would possess complete cubic symmetry.Such an arrangement in the structure of III-NH,Br and III-NH,I is consistent with the absence of a low lattice vibration frequency from their Raman spectra. (A similar hypothesis had been advanced by A. Hettich 39 from a consideration of piezoelectric properties.) Menzies and Mills showed that on this basis a plausible explana- tion could be given of the opposite sign of the volume changes a t the I11 + I1 transition in ammonium chloride and bromide. Tetrahydrides of Carbon Silicon and Germanium. Table I1 gives the absolute temperatures and heats of transition and fusion for the compounds so far investigated. The values of AH for the transitions (except that in CH444 . . CD,44 . . SiH,45 . . GeH446 . . CH,D44. . I III-+II. I I1 + I. T O x . - 15-88 22-25 13-20 - AH - 13-6 19.8 130.7 - 1' OR.20-42 23.19 27.10 63.45 76.55 a Ti 1 5 7 44.4 58.7 166 129.6 Fusion. T OK. 90-64 90.42 89.78 107-26 88-48 1 AH 224 217.5 215-7 159.6 199.7 4 3 Proc. Boy. SOC. 1935 A 148 407. 4 4 K. Cliisiris and 3,. Popp Z. physikul. G'Iwm. 1940 B 46 63 4 5 K. Clusius ibid. 1933 B 23 313. 4 6 K. Clusiim and G. Faber ibid. 1943 B 51 352. 78 QUARTERLY REVIEWS silicane) are the amounts of energy in calories required to heat one mole of the substance through a short temperature range enclosing the transition ; ie. they include the " normal '' contribution from cp for which it is difficult to make an exact allowance. For silicane the figure represents the true heat of transition. All of these transitions are gradual and all show hysteresis? except perhaps that in silicane. The hysteresis in the methane transition has been particularly carefully inv-estigated by A.Eucken and E. Barth0lom6.~ In addition to the transitions recorded in Table 11 III-GeH shows an anomaly in the heat capacity cp rises gradually to a maximum value of 21 cals./mole at 62.9" K. ar,d then falls abruptly according to K. Clusius and G. Faber,46 to 13 cals./mole. No simultaneous change can be detected optically (by means of a polarisation microscope) and the anomaly may perhaps be an example of a genuine second-order transition. An X-ray investigation of methane by H. H. Mooy 4 7 gave no evidence of any alteration in the face-centred cubic structure a t the transition. K. Clusius and his colleagues have studied all forms of the above substances with a polarisation microscope.* For the methanes forms I and I1 are all isotropic but III-CH,D and III-CD are doubly-refracting.I-SiH and I-GeH both show weak double refraction which is much more pronounced in the low-temperature forms. The I11 + I1 transition in germane is detectable in this way but only a slight change in optical behaviour accom- panies it. It seems therefore that the II - + I change in germane and silicane produces a high-temperature form of greater internal symmetry? in contrast to this transition in the methanes. Although the transition in silicane begins with an anomalous rise in cP 88(3" of the heat of transition is absorbed within lo and it may well be that the change begins gradually but reaches completion in a first-order phase change. It will be seen from Table I1 that the entropy change at the transition is greater than the entropy of fusion.The presence of two transitions in mono- and tetra-deuteromethane suggests that it is methane which is abnormal in only having one. In the lattices of these compounds almost identical intermolecular forces prevail and torsional oscillations will have the largest frequencies and hence the greatest zero-point eriergies for the lightest molecules. A potential barrier restricting rotation will have almost exactly the same absolute height in all three lattices and will therefore first be overcome by methane molecules which retain the most energy a t the absolute zero. (It is significant that the temperature of the I1 -+ I transition increases with replacement of H by D. and that AH,,, for CH is very much less than for CD,.) Probably therefore the form III is one in which methane is incapable of existing (at least at ordinary pressures) on account of its high zero-point energy.Interesting experiments were carried out by E. Bartholome G. Drikos and A. Eucken 48 on mixed crystals of CD4 and CH,. They 47 Proc. Acud. Sci. Amsterdam 1931 34 550. 4 8 2 . physikal. Ghem. 1938 B 39 371. * See ref. (46) for a summary of this work. STAVELEY TRANSITIONS M SOLIDS AND LIQUIDS 79 found that the temperature of the upper transition varies linearly with the deuterium content (a striking demonstration that a co-operative change is involved) and that the transition never becomes more diffuse than in the pure compounds. The temperature of the lower transition in tetradeutero- methane on the other hand falls more and more rapidly with increasing hydrogen content and the specific heat anomaly becomes less and less marked and finally vanishes a t about 20% CD,.In mixed crystals of methane and krypton 49 the I1 + I transition becomes less pronounced and its temperature lower with increasing krypton content and when this has reached about 30% the transition disappears. This result is readily comprehensible if the transition involves a co-operative librational-rota- tional change for replacement of tetrahedral methane molecules by the spherically symmetrical rare-gas atoms will clearly weaken the forces tending to orientate any one methane molecule and therefore reduce the height of the potential barrier and also make less acute the dependence of this height on the fraction of molecules already rotating. A. Eucken and H.Veith 49 carried out an analysis of the heat capacity of solid methane and solid solutions of methane and krypton and by skilful use of rather fragmentary data for the required compressibilities and coefficients of expansion arrived at values for the rotational heat capacity of the methane molecules in the lattice. Both for the pure substance and for the solid solutions from about 50" K. upwards these are remarkably near the of a classical three-dimensional rotator. Indeed in the mixture richest in krypton its values even a t lower temperatures (where quantisa- tion becomes important) are still very close t o those calculated for gaseous methane. This evidence for attributing rotational freedom to the methane molecules in form I is supported by the nuclear magnetic rcsonance method.31 The absorption band narrows considerably in the neighbourhood of the transition as the temperature is raised.Hydrogen and Deuterium Halides. Some facts about these substances are recorded in Table 111. The values of AH for the transitions in the bromides and iodides have the same significance as in Table 11. The only sharp transition is that in hydrogen chloride from a form of very low symmetry (11) to a cubic structure With the change I1 -+ I the dielectric constant rises abruptly l8 but from a quantitative considera- tion of the polarisation-temperature relationship for phase I G. Mettner 50 concluded that the molecules are not rotating freely in this phase. According t o a provisional report,51 this conclusion is confirmed by the nuclear magnetic resonance method the absorption line being equally broad above and below the transition point.Presumably therefore the molecules in the high- temperature form undergo torsional oscillations about disordered axes but are capable of changing their orientation sufficiently frequently to account for the high dielectric constant. The infra-red and Raman spectra 54 49 Ibid. 1936 B 34 275; 1937 B 38 393. slF. Bitter et al. M.I.T. Quarterly Progress Report Oct. 1947. 6 2 E. Lee 62. B. B. M. Sutherland and C. K. Wu Proc. Roy. Soc. 1940 A 176 493. Ann. Physik 1938 33 141. 80 QUARTEBLY REVIEWS likewise provide no evidence of molecular rotation in the solid but instead show that the condensation of gas to liquid involves a considerable change in the intramolecular vibration frequency comparable with that which the frequency associated with a hydroxyl group experiences when the group enters into hydrogen-bond formation.Thus in the condensed states of hydrogen chloride there would appear t o be marked intermolecular association. TABLE 111" I 1II+ 11. 1 II+1. I I I I 17 O K . I I H C l . . . - DC1. . . - I-IBr. . . 89.76 DBr. . . 93.5 HI . . . 70.1 DI . . . 77.3 AH T OK. A H - 98.36 284.3 - 105.03 320.1 160.1 ' 113'6211 -f E}264.5 llG.86E -+ I 169.7 120.26 303.0 146.8 125.68 359.9 175.6 128.28 386.4 Fusion. T OK. A H 158.91 476.0 158.44 473.2 186.28 675.1 185.62 574.2 222.31 686.3 221.23 684.3 not yet available. The hydmgen halides were studied by W. F. Giauque and R. Wiebe J. Amer. Chem. SOC. 1928 50 101 (HC1); ibid. p. 2193 (HBr); ibid. 1929 51 1441 (HI). Hydrogen bromide unlike any other of the halides including deuterium bromide has three transitions.In mixed crystals of these two bromides the region of existence of the extra form designated E in Table 111 diminishes with increasing deuterium content and vanishes a t 470/ of DBr.42 From the similarity between DBr and HI i t would appear to be HBr and not DBr which is abnormal. From X-ray investigations it appears that hydrogen iodide has a face-centred tetragonal lattice in all its forms but unambiguous conclusions about the structure of hydrogen bromide have not been reached in this way. Polarisation microscope studies on HBr DBr and HI have revealed that I is always isotropic and I1 and I11 aniso- tropic.42~ s3 The dielectric constant of hydrogen bromide rises very rapidly as it approaches the 111-11 transition and thereafter drops almost as rapidly to a fairly steady val.me.lsb> 64 It is not certain whether the mole- cules of hydrogen bromide and iodide can rotate freely in their lattices.They are more likely to do so than those of hydrogen chloride in view of their smaller dipole moments. The 111 + I1 transition in hydrogen bromide exhibits hysteresis which has been carefully examined both thermally 5 5 and by dielectric constant rnea~urements.~~ The width of the hysteresis loop as determined by heating s3 A. Kriiis and R. Kaischew 2. physiknl. Chem. 2935 B 41 427. ji G . DamkiihIer Asm. Physik 1938 31 76. 65 A. Eucken and W. Giittner Gottingen Nuchr. Math.-Phys. K1. 11 1936 2 167. STAVELEY TRANSITIONS IN SOLIDS AND LIQUIDS 81 and cooling curves was found to remain the same even if a sample previously warmed to a point about half-way up the hysteresis loop was inoculated with the high-temperature form or alternatively subjected to supersonic waves for six hours.The dielectric-constant study did in fact show a slight shrinking of the hysteresis loop with time but limiting conditions wcre reached the hysteresis still persisting beyond which no further change was observable. Many other substances besides those discussed above have transitions of considerable interest. They include 1iitrates,5~ perchlorates,57a and other salts 57b in which there is evidence of anion rotation ; resorcinol ; 58 “ Seignette-electric ” substances like potassium dihydrogen phosphate ; 59 and numerous organic compounds with long hydrocarbon chains where the transitions are probably connected with the onset of the rotation of the chain about its axis.6o In addition many new transitions have been observed in a variety of compounds a t high pressures.61 The nature of the transition in liquid helium which of course has nothing to do with molecular rotation is fully discussed in W.H. Keesom’s book on this element. The Reviewer wishes t o thank Dr. A. H. Cooke for helpful discussions and Mr. C. J. Mandleberg for assistance in surveying recent literature. 56F. C. ISracek J . Amer. Chenz. SOC. 1931 53 2609; F. C. Kracek E. Posnjnk and S. B. Hendricks ibid. p. 3339 ; J. B. Austin and R. H. H. Pierce ibid. 1933 55 661 ; C. Finbsk and 0. Hassel 2. physikal. Ghem. 1937 B 35 25. 67 Idem ( a ) ibid. 1936 B 32 130; ( b ) ibid. p. 433. 68 J. M. Robertson and A. R. Ubbelohde Proc. Roy. Sac. 1938 A 167 136. 6B W. G. Cady “ Piezoelectricity ” (McGraw-Hill Book Co. 1946) ; C. C. Stephenson ~t at. J . Amer. Chem. SOC. 1944 66 1397 and following papers ; J. C. Slater J . Chem. Physics 1941 9 16. soA. Miiller Proc. Roy. SOC. 1932 A 138 514; W. 0. Baker and C. P. Smytli. J . Amer. Chem. Sac. 1938,60 1229 ; J. C. Southard R. T. Milner and S. B. Hendricks J . Chem. Physics 1933 1 95. 61 P. W. Briclgman “ The Physics of High Pressures ” (G. Bell and Sons 1931) Chap. 8. F

ISSN:0009-2681    

DOI:10.1039/QR9490300065

出版商:RSC    

年代:1949

数据来源: RSC

摘要:

THE CONSTITUTION OF PORTLAND CEMENT By F. M. LEA O.B.E. D.Sc. F.R.I.C. (DIRECTOR OF BUILDING RESEARCH DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH) THE complex anhydrous silicate and aluminate products which are exempli- fied by the igneous rocks and certain industrial materials have been the subject of much investigation and none more intensively than Portland cement an industrial product of first importance. Studies in these fields of high-temperature chemistry demand specialised techniques and progress has run parallel with the development of modern physicochemical methods in general and of new techniques appropriate to the subject in particular. The study of the constitution of Portland cement has had as one of its objects the determination of the nature of the compounds or mineral species it contains and the origin of its cementing properties.Another purpose has been the relation of the constitution of the product to its composition and conditions of manufacture and to its mode of hydration and technical properties. It would be arbitrary to attempt to draw any distinction between those studies which have been pursued because of their scientific interest per se and those which have been followed because of their technical importance but the present Review will be confined largely to the chemical and mineralogical aspects of the subject. Portland cement is manufactured by burning a mixture of suitable finely ground calcareous and siliceous materials such as limestone chalk clay and shale. The large rotary kilns normally used for burning reach an extreme length of some 500 ft.and are slightly inclined to the horizontal so that as the kiln rotates the raw materials fed in a t the upper end travel slowly down to the lower end from which the kiln is fired and where the burnt product is discharged. The fuel used is most commonly pulverised coal blown in by an air blast but oil or gas is also used when economic. The raw materials as they progress down the kiln are first dried followed by dissociation of the calcium carbonate and the commencement of solid reactions between the lime and the clay. At about 1280" partial melting commences and the reactions accelerate and are finally completed in the hottest zone at a tem- perature of 1350-1500" when some 20-30% of the mix becomes liquid. This causes the materials to coalesce into small nodules mostly from 8 to 9 in.in diameter known as Portland cement clinker. The latter is then ground to a fine powder with a small addition of gypsum to control the rate at which the material sets on mixing with water. Though lime alumina ferric oxide and silica are the major components of Portland cement there are also present minor constituents which exercise a considerable influence on the constitution of the product. The com- position of different clinkers falls within the following percentage range CaO 60-67 ; SiO, 17-25 ; Al,O, 3-8 ; FezO3 0.5-6 ; MgO 0.5-5.5 ; Na,O + K,O 0-4-1.3 ; TiO, 0.1-0.4 ; SO, 0.1-0-5. Contents of 82 LEA TEtE CONSTITUTZON OF PORTLAND CEMENT 83 Mn,O varying from 0.5 to 3.0% are also found when certain types of blast- furnace slag are used as raw material for cement manufacture.The investigation of the constitution of Portland cement involves the determination of the manner in which these various oxides are combined a t the temperature of burning and the changes which occur during cooling. Despite the limited amount of melting which takes place there is good evidence that Portland cement mixes approach closely a state of chemical equilibrium a t the burning temperature apart from a small residue of uncombined lime which has not had sufficient time to react during the burning. On cooling however the equilibrium is not fully maintained owing to the sluggishness of some reactions and crystal inversiom and to the failure in varying degree of the liquid phase to crystallise. Essentially therefore Portland cement is to be regarded as an example of frozen equili- brium reproducing in its cooled state the equilibrium existing a t or near the burning temperature but modified in some degree by partial change towards the true equilibrium at room temperature.The more important compounds formed namely 3CaO,SiO, 2CaO,Si0, 3CaQ,Al,Q3 and 4Ca0,A1203,Fe20, are modified to a small extent by solid solution with other components and the first two exhibit polymorphic transformations. The compounds formed by the minor components add their own complications. Methods of experimental investigation have been needed which would determine the equilibria existing a t the burning temperature enable the changes occurring on cooling to be traced and permit the identification of particular mineral species in the cooled clinker. The study of phase equilibria has been one essential line of attack using methods common to the wider sphere of mineralogy.Such investigations on silicate systems at high temperatures cannot be carried out by the method of cooling curves used in the study of meta,ls since crystallisation and inversion are too sluggish. The alternative method of heating curves can often be very useful for checking inversion temperatures of compounds exhibiting polymorphism and the points of initial and complete melting but taken alone the interpretation of the results is frequently uncertain. The primary tool and an elegant one is the quench met'hod. In this a small charge 0.1 g. or less of the desired oxide composition is placed in a small platinum bucket suspended by a fine platinum wire and heated in a vertical furnace at a constant temperature until equilibrium is attainecl.The supporting wire is then fused and the charge allowed to drop into water or mercury to quench the equilibrium. This freezes any liquid that was present a t the furnace temperature to a glass in which are embedded crystals of the solid-phase compounds. By examination under the petrographic microscope of powdered samples from a series of preparations of varying composition the temperatures of final melting and of the appearance of different crystalline phases can be determined and the phase equilibrium diagram a complete polytherm of the Bystem built up. For temperatures up to 1650" the furnaces used are normally wound with Pt-20% Rh wire and automatically controlled to maintain a temperature constant to & 1" over a small central section in which the charge is held.Syatems of four, 84 QUARTERLY REVIIEWS FIa. 1 System CaO-A1,O ,-SiO,. Abbreviated Notation ; C = CaO A == Al,O, S = SiO,. FIG. 2 System C'aO-2Ca0,Si0z-5Ca0,3A1z03-4Ca0,A1203,Fe,0,. Abbreviated Notation C = CaO A = A1,0, F = Fez03 S = SiO,. LEA THE CONSTITUTION OF PORTLAND CEMENT 85 and to a limited extent even five components have been examined by this means and much of the remainder of the nine-component system involved in Portland cement studied by selection of suitable “ cross-sections ” of the whole. The phase-equilibrium diagrams illustrated later (Figs. 1 and 2) are projections of the polytherm on to the composition base an equilateral triangle in the case of ternary systems and a regular tetrahedron in that of quaternary systems.The method of plotting is therefore different from the representation of solubility curves at some fixed temperature commonly used for aqueous systems. Instead the diagrams show the composition regions or primary phase fields in which any one solid is the first to separate when a completely liquid mix is allowed to cool. With the aid of tempera- ture contours the course of crystallisation can be followed and the proportion and composition of the solid and liquid phases present a t any desired tem- perature ascertained. The effect of deviations from the true equilibrium path during cooling can also be estimated. X-Ray methods have been considerably used for the determination of phase-equilibrium diagrams for nietallic systems but their scope is more limited in silicate systems owing to the low symmetry of many of the com- pounds that arise and the consequeiit lack of sensitivity in the detection of the first appearance of particular solid phases.There still remains however a wide field of use for the detection of individual compounds when present in sufficient quantity in mixes for the study of inversion phenomena with high temperature cameras and fGr structure analysis. Work of the last type has until recently been handicapped by the small size of the crystals obtainable from some of the most important compounds restricting the examination to powder preparations. Recently however R. W. Nurse at the Building Research Station has developed a technique for growing single crystals from silicate melts and crystals of for example pure SCaO,SiO and its solid solutions as large as 0.5 mm.in diameter have been obtained. Various microscopic techriiques are used. Individual mineral con- stituents can be identified in powder preparations by measurement under the microscope of optical properties. Thin sections of synthetic silicate melts can be prepared for examination by transmitted light in the same way as in the petrographic study of rocks. The met,allurgical technique of polishing and etching surfaces for examination by reflected light is also applicable though rather more difficult than with metals and has proved an invaluable weapon for the study of the miiieralogy of cements. By the use of selective etches different mineral species can be brought into prominence identified and estimated. Other measurements such as microreflectivity have proved their usefulness in some cases.As a still further step in technique it has proved possible though more difficult to 21st Congress Ind. Chem. Brussels 1948. * See 33. H. Bogue “ Chemistry of Portland Cement ” Rheinhold Publishing Corporation U.S.A. 1947 ; F. M. Lea and C. €I. Desch ‘‘ Chemistry of Cement and Concrete ” Edward Arnold London 1935, 86 QUARTERLY REVIEWS polish and etch thin sections which can be examined by both reflected and transmitted light. In general it is difficult to identify interstitial material by examinahion under transmitted light but a very clear differentiation can often be obtained by reflected light with selective etching. A comparison of Figs. 3 and 4 will illmtrate this. The normal methods of mineral separ- ation by sedimentation in heavy liquids or centrifuging also find application.Electron microscopy has so far found its greatest use in the study of the hydration of cements where the grain size of the products is often extremely small. Special interest has attached to the presence of a glass phase in Portland cement since this has some very significant effects on the technical properties of the material in use. Its coinposition can be determined approximately from the phase-equilibrium data and its quantity estimated again approxi- mately by microscopic counts on polished surfaces or by a heat of solution method. In the latterY3 the heat of solution of the cement clinker before and after annealing is determined in a nitric-hydrofluoric acid solvent and the glass content estimated from data on the heat of crystallisation obtained in a similar manner.Two of the individual constituents of Portland cement clinker free calcium oxide and free magnesia,5 the mineral periclase can be determined by direct chemical methods. The quantity of the former is of interest since it indicates the extent to which complete equilibrium was not obtained during burning and both are important in relation to the volume stability of the set and hardened cement. The study of the constitution of Portland cement commenced with Le Chatelier who is regarded as the father of cement chemistry. His first contributiog appeared in 1883 and his thesis for the degree of Doctor of Science published in Paris in 1887 and in an English translation,* remains a classic. The basic system CaO-Al,O,-SiO necessary to the understanding of Portland cement was the first ternary silicate system studied at the Geophysical Laboratory Washington D.C.U.S.A. and its publication by R. W. Rankin and F. E. Wright 7 in 1915 is a landmark in the study of the natural and artificial silicates. It laid the method of approach and the basis of many of the high-temperature techniques from which later developments have been derived. The equilibrium diagram of the system Ca0-A1,0,-Si02 is reproduced in Fig. 1. The field of Portland cement compositions is such that a t equili- brium the compounds 3Ca0,Si02 2CaO,SiO, and 3CaO,Al,O are formed together with free CaO if more than a certain proportion of lime is present. A brief inspection of the diagram will show however that a t a temperature of say 1500" the liquid in equilibrium with 3CaO,SiO as solid phase or with a W.Lerch and L. T. Brownmiller J . Res. Nat. Bur. Stand. 1937 18 609. 4 W. Lerch and R. H. Bogue Ind. Eng. Chern. Anal. 1930,2,296 ; B. Bakewell and G. E. Bessey Building Research Spooial Report NO. 17 H.M.S.O. 1931. R. H. Bogue ref. (2) p. 75. 6 " Experimental Rssssrches. on the Constitution of Hydraulic Mortars " tranalated 7 Anzer. J . Sci. 1915 33 1 ; see also J. W. Greig {bid. 1927 13 41. by J. L. Mack McGraw Publishing Co. New York 1905. FIG. 3 Portland cement clinker thin section by transmitted light ( x 350) FIG. 4 Portlarid cenieizt clinker etched polished surfciccl by reflected light ( s 600) LEA THE CONSTITUTION OF PORTLAND CEMENT 87 either CaO or 2CaO,SiO in addition has a compositioh failing on the low rime side of the composition line from 2CaO,SiO to 3CaO,Al,$.To maintain equilibrium on cooling therefore the liquid must react with solid 3Ca0,Si02 to remedy its deficiency in lime. This is one of the sluggish reactions referred to earlier which fails to occur completely a t the rate at which commercial Portland cement clinker is cooled. Evidence of its partial occurrence is however to be seen in Fig. 4 where the dark 3CaO,SiO crystals have jagged and roughened edges resulting from this reaction. Separation of a liquid magma at some stage of its crystallisation into solids which are more basic and a liquid which is more acidic or vice versa than corresponds to the final equilibrium state on cooling is not confined to the artificial silicates but is also characteristic of the igneous rocks.It is indeed typical of systems containing compounds which decompose below their melting point or which have an incongruent melting point such as the tricalcium silicate and tricalcium aluminate which occur in Portland cement. Studies on the system CaO-Al,O,-Fe,O * showed that a ternary com- pound 4CaO,A1,O3,Fe,O exists and more recently evidence has come forward for a further compound 6Ca0,2Al2O,,Fe,0 forming a complete solid solution series with it. The quaternary system Ca0-2Ca0,Si02- 5Ca0,3A1,0,*4Ca0,A1,0,,Fe203 which forms a complete system within the larger CaO-Al,O,-Fe,O,-SiO system contains within itself all the com- positions of lime alumina ferric oxide and silica which are of concern in the chemistry of Portland cement. The phase-equilibrium diagram l o of this system is shown in Fig.2. From it there can be derived the compositions of the liquids formed during the burning of Portland cement and the changes they should undergo if equilibrium is maintained on cooling. It also indicates that the compounds formed a t equilibrium from a mix of Port- land cement composition are 3CaO,SiO, 2CaO,SiO, 3CaO,Al20, and 4Ca0,A1,0,,Fe,03 (or its solid solution with 6Ca0,2A1,0,,Fe,03). A more detailed examination than is possible from the diagram further shows that with mixes of low Al,O Fe,O ratio the liquids contain excess of CaO and that if equilibrium is to be maintained on cooling reaction must occur between solid BCaO,SiO and liquid to form 3Ca0,Si02. This is the reverse of the case found in the Ca0-A120,-Si0 system but the Al,O Fe,O ratio of most Portland cements is such as t o make them behave similarly to the latter in this particular respect.Since however the liquid-solid reaction is too slow to occur to more than a limited extent during the cooling of the clinker the cooled cement represents a somewhat complex frozen equilibrium. The compounds formed by the minor components of Portland cement are still not entirely clear but much progress had been made by phase- equilibrium investigations and other means. In general they pass into the liquid phase during burning and if this fails to crystallise on cooling 8 W. C. Hansen L. T. Brownmiller and R. H. Bogue J . Amer. Chem. SOC. 1928 50 396; H. F. McMurdie J . Res. Nat. Bur. Stand. 1937 18 476. M. A. Swayze Arner. J . Sci. 1946 244 1 65. l*F. M. Lea and T.W. Parker Phil. Trans. 1934 A 234 1. * Reoent work indicates that the true composition of this compound is 12Ca0,7A1,08. 88 QUARTERLY REVIEWS most of the minor components remain in the glass formed. Study of the quaternary system l1 Ca0-Mg0-2Ca0,Si02-5Ca0,3A1203 and of part of the quinary system9 containing iron compounds in addition has shown that magnesia is soluble in the liquid phase formed during the burning of Portland cenoent to the extent of about 5%. Any excess of MgO is uncombined and present as the mineral periclase at the burning temperature and this is also formed from the liquid phase on crystallisation. The alkalis K20 and Na20 behave very differently from one another. The former combines preferentially with any sulphur trioxide present ,I2 and as molten potassium sulphate is immiscible with the clinker liquid it crystallises direct on cooling.Excess of K20 above that required for this reaction enters into solid solution in or forms a compound l3 with dicalcium silicate of the formula K20,23Ca0 12Si0,. The information regarding sodium oxide is rather less definite but it is probably capable of being present in several forms. It dissolves in the clinker liquid and the glass formed if this fails to crystallise can hold up to 8% of Na20.14 From investigations on portions of the quaternary system l4 Na20-CaO-Al,03-Si02 it seems that a compound Na20,8Ca0,3A1203 or a solid solution of this with 3Ca0,A1203 is probably formed on crystallisation of the liquid phase. Soda also enters into solid solution to a small extent in the dicalcium silicate and precipitates as inclu- sions if this inverts on cooling to the /?-form.Titania 15 may form 3Ca0,2Ti02 or CaO,TiO,. Manganic oxide l6 can substitute for Fe,03 in the compound 4Ca0,A120,,Fe203 and any Mn20 in Portland cement is probably present in it solid solution of this type. The two most important compounds of Portland cement are tri- and di-calcium silicate for they are primarily responsible for the cementing properties. Though the amounts of other components which these silicates can take up in solid solution are small they are nevertheless important for they influence the reactivity to water and also the polymorphic changes which the compounds can undergo. Tricalcium silicate is an unusual compound for it is stable l o only between 1250" and 1900" and at lower or higher temperatures decomposes to form the same products CaO and 2Ca0,Si02.Its rate of decomposition below 1250" is very slow and it remains in a metastable state indefinitely at ordinary temperatures. Only the upper decomposition point appears in the Ca0-A1203-Si02 diagram for the liquidus temperatures along the boundary between the fields of 3CaO,SiO and 3Ca0,A120 range from 1455" to 1470". By the addition of miiieralisers however the liquidus temperatures can be much reduced and the field of 3CaO,SiO then tapers to a point a t both ends. This is illustrated by the phase diagram obtained by W. Eitel17 for the system Ca0-2CaO7Si0,-CaF which is reproduced in Fig. 5. If the lower decomposition point of tricalcium silicate were another 100-200 O higher l 1 H. F. McMurdie and H. Insley J .Res. Nat. Bur. Xtand. 1936 16 467. 1 2 W. C. Taylor ibid. 1942 29 437 1 4 K. T. Green and R. H. Bogue ibid. 1946 36 187. l6 F. M. Lea and R. W. Nurse unpublished l6 T W. Parker private communication lS Idem ibid. 1941 27 311. 1' Zement 1938 27 455 469. LEA THE CONSTITUTION OF PORTLAND CEMENT 89 its formation in Portland cement would be difficult or impossible and Portland cements with the speed of hardening known today would not exist. There has been difficulty in determining the extent to which 3CaO,SiO can take other components into solid solution but as formed in Portland cement it may contain up to 3% of A1,03 Fe,03 CaO and MgO. Tricalcium silicate is also a constituent of open-hearth slags and crystals from this source have been found to contain some 3 % of FeO and MnO.Very recently Bernal and Jeffery have carried out an X-ray analysis on single crystals of pure tricalcium silicate grown at the Building Research Station by the technique developed by Nurse and on similar solid solution crystals. The pure compound is found to exist in two polymorphic forms a high-tempera- ture trigond form and a lower-temperature triclinic form. Th2 inversion CaF 2572" 1388 FIG. 5 Sysfern CaO-ZCaO,SiO ,-CaF,. temperature is still uncertain and may be above 1600" for the pure com- pound but lower for the solid solutions. The minerals found in Portland cement or basic open-hearth slags all have the trigonal form which is apparently transformed less readily when containing limited amounts of other oxides in solid solution. Dicalcium silicate has long been known to exist in three enantiotropic forms a $ and y of which the first two have cementing properties while the y-form is very inert to water and has no cementitious value.The ,8 + y inversion which occurs at 675" is accompanied by a volume increase of some loyo resulting in the break-up of the solid into a fine powder. This is the cause of the " dusting " during cooling or subsequently of some types of blast-furnace slag which contain dicalcium silicate. A similar behaviour is sometimes found to occur with Portland cement clinker stored for a 90 QUARTERLY REVIEWS considerable time. With the pure compound the inversion occurs readily and indeed it is diacult to cool it sufficiently rapidly to stabilise the ,&form but with quite small amounts of other components in solid solution the inversion becomes very sluggish and the p-form can then be preserved indefinitely.Both a- and P-dicalcium silicate can take small amounts of numerous other oxides such as SiO, Al,O, MgO Na,O B,O, or P,O into solid solution with a lowering of the inversion temperature indicating a greater solubility in the a- than in the /3-form. With CaO the inversion temperature is raised so that the solubility must be greater in the /I-fGrm. Because of the influence of SiO and CaO in respectively lowering and raising the inversion temperature its precise value is in doubt but it appears to be either 1438" or 1456". The a-form has long been supposed t o be monoclinic or triclinic and the /?-form orthorhombic but in 1942 M. A. Bredig l9 published the first of a series of papers on the structure of compounds of the A2XQ type.These compounds e.g. K,SQ4 Na2SO4 CaNaP04 all occur in more than one modification but in their high-temperature (a) form they are isomorphous and have hexagonal symmetry. Bredig therefore suggested that a-Ca,SiO was hexagonal and he was also led to postulate the existence of an ='-form because the compounds or solid solutions K20,23Ca0 12Si0 and 27Ca0,P,05,1 2Si0 have a structure corresponding to D-K,SO with a symmetry lower than a but different from @-Ca,SiO,. This "-form was considered to have a range of stability between the a- and the ,%form. Recently C. E. Tilley and H. C. G. Vincent 2o have found the a'-form in metamorphised limestone from Scawb Hill and in spiegeleisen slag and have designated this new phase bredigite. Confirmation of the hexagonal spmmetry of a-Ca,,Si04 has been obtained by A.V. Van Valkenburg and H. F. McMurdie 21 from an X-ray powder diffraction pattern taken in a high- temperature camera a t 1500" using a Geiger counter in place of a photo- graphic film. A solid solution of Cs,,SiO containing 10% of CaNaPO prepared at the Building Research Station has also recently been found to have the a-structure at 1350". From other recent evidence obtained by Nurse a t the Building Research Station the a'-form is probably stable only a t the highest temperatures inverting to a as the temperature is lowered. For the pure mineral the inversion temperature probably lies between 1650" and 1750" but is lowered by solid solution. The attention that has been paid to the crystal form of tri- and di-calcium silicates and also of other cement compounds reflects the interest in the origin of their reactivity and cementing properties.Both E. Branden- berger 22 and Bredig l9 have endeavoured to relate with quite different results the variation in reactivity to differences in the co-ordination number 18 E. S. Newman and L. S. Wells J . Res. Nat. Bur. Stand. 1946 36 137 ; K. T. Greene ibid. 1944 32 1. 19 J . Physical Chem. 1942,46,747 801 ; 1943 47 587 ; 1945 49 537 ; Amer. Min. 1943 28 594. ao Min. Mag. 1948 28 255. 2% Schweiz. Arch. Angew. Wiss. Tech. 1936 2 45 ; Symposium on the Chemistry of J . Res. Nat. Bur. Stand. 1947 38 415. Cements Stockholm 1938 pp. 122 174. LEA THE CONSTITUTION OF PORTLAND CEMENT 91 of the calcium atoms and the part these play in the crystal structure ; in the absence of complete structural analysis no generally accepted conclusions have yet been reached.With the recent development of a technique for growing single crystals large enough for X-ray analysis further progress now becomes possible. Data on the heats of formation of the cement compounds from the oxides CaO Al,O, SiO, and Fe203 are available and also the heats of hydration. The data are shown in the table but their degree of precision varies. Thus the heats of formation of the silicates are in doubt to & 0-7 kcal. per mol. and those of the alumina-containing compounds to & 1 kcal. per mol. owing to uncertainties in the heat of crystallisation of amorphous silica and of the heat of the reaction 2Al(s) + SO2(& = Al,O,(s) the values of which enter into the respective computations.The formation of SCaO,SiO from #?-2Ca0,Si02 and CaO it will be noted is endothermic. Compound. 3Ca0,Si02 . . . . /3-2Ca0,Si02 . . . y-BCaO,SiO . . . 3Ca0,A120 . . . 4Ca0,A1,0,,Fe20 . CaO. . . . . . MgO . . . . . Heat of format,ion from oxides at 20". Kcal per mol. 29.4 29.8 30.9 2.0 10.0 - - Cal. per g. 129 173 179 7 21 - - Heat of hydration at 20'. Kcal. per mol. 27.4 10.7 57.8 48.6 15.7 8.2 - Cal. per g. 120 62 214 100 279 203 I From the detailed information now available on the constitution of Portland cement it is possible to calculate its approximate compound composition on certain assumptions to relate this to the properties of cements and to check it by microscopic measurement on etched polished surfaces of the cemBnt clinker. A simple calculation of the main compounds can be made fiom the oxide analysis assuming that the cement has crystallised completely and is in a state of equilibrium.For different types of Portland cement the content of 3CaO,SiO varies from 10 to 65% of 2Ca0,Si02 from 5 to GOYo of 3CaO,&O3 from 3 to 15y0 and of 4Ca0,Al,03,Fe,03 from 5 to 15% except for white Portland cements where it falls to below 2%. The content of uncombined lime varies from almost zero to a few units yo depending on the hardness of burning. Alternatively other assumptions may be made as to the degree of crystallisation of the clinker liquid and this can be checked by determination of the glass content of the clinker and the subsequent calcidation of cornpoilnd content modified in various ways. Portland cement clinkers are found to vary very considerably in their contents of glass the values ranging from almost zero up to 20% or more.The contents of alumina and iron compounds decrease as the glass increases since they are found during the crystallisation of the clinker liquid. The properties of Portland cements are closely related to the compound content but are affected also by the fineness of grinding and other factors such as the proportion of water used to mix them. I n general tricalcium 92 QUARTERLY REVIEWS silicate makes the major contribution to the strength developed over the first 28 days after mixing with water while the contribution made by dicalcium silicate becomes important between 7 and 28 days and practically equals that of tricalcium silicate wit,hin 90 days. Perhaps the major problem remaining here is the influence of solid solution of minor com- ponents and of crystal form on the reactivity and rate of strength develop- ment.There are also other technical properties such as the heat of hydration which becomes of major importance when large masses of concrete are placed as in dams and the volume changes which the set cement under- goes with change in moisture content that can be rela,ted to the mineralogica.1 make-up of the cement and the nature of its hydration products. The hydrated compounds formed from Portland cement present a still more complicated problem 2$ 23 than that of its constitution and only the broadest outline can be given here. The aqueous systems involved in the determination of final equilibria are far from easy to study and demand all the resources which modern physicochemical techniques can bring to bear for solubilities are low and metastable equilibria common.The systems CaO-Al,O,-H,O 24 and CaO-Si0,-H,O 2 5 are now reasonably well though not entirely known and also the quaternary system 26 Ca0-A1,0,-S03-H,0 which is implicated because of the addition of gypsum to Portland cement to control its setting time. The quinary systems 27 formed by the addition of Na,O or K,O to CaO-A1,0,-SO3-H,O and the quaternary 28 CaO-Na,O- Si0,-H,O have also been studied and to some extent the quaternary system Ca0-A1,0,-Si0,-H20 and the systems involving Fe203. It is perhaps characteristic of the relative difficulty of their study that the information on the equilibria in many of these systems at temperatures above 100" under high steam pressure is more precise than that at normal temperatures.With the former well-crystallised products are obtained for example 3Ca0,Si0,,2H20 from tricalcium silicate and several dicalcium silicate hydrates from BCaO,SiO, but with the latter amorphous or sub-micro- crystalline materials are frequently encountered. It is in this field that the introduction of the electron microscope promises to be of considerable help. The reaction of SCaO,SiO with water produces a supersaturated solution of the same stoicheiometric proportions from which Ca(OH) and a hydrated calcium silicate separate while with P-ZCaO,SiO in a limited amount of water only traces of calcium hydroxide appear. The hydrated silicate is an apparently amorphous product but G. E. Bessey 23 has obtained micro- scopically visible crystals from ,f?-2Ca0,Si02 after hydration for a year.The formula ascribed to the compound by R. Hedin 29 is 2Ca0,Si0,,4H20. Other evidence 2 from phase-equilibria studies indicates that at. a pH value 2 3 Symposium on the Chemistry of Cements Stockholm 1938. 2 4 L. S. Wells W. F. Clarke and H. F. McMurdie J . Res. Nut. Bur. Stand. 1943 2 6 F. E. Jones Trans. Faruday Soc. 1939 35 1484 ; J . Physical Ghem. 1944 48 27 Idem ibid. 1945 48 356 379 ; G. L. Kalousek ibid. 1945 49 405. 2s Idem J . Res. Nut. Bur. Stund. 1944 32 285. 08 Proc. Swedish Cement and Concrete Institute 1945 No. 3 30 367. 311. 2 6 H. H. Steinour Chemical Reviews 1947 40 391. LEA THE CONSTITUTION OF PORTLAND CEMENT 93 which is very close to and may be slightly above that of a saturated lime solution this hydrated disilicate hydrolyses to form 3Ca0,2Si02,aq.as another apparently amorphous phase. There is still therefore some uncertainty as to which of these silicates is formed from Portland cement. But this does not appear to be the final equilibrium product since with alumina present as well the formation of hydrated calcium aluminosilicates is possible. After hydration for three years H. P. Flint and L. S. Wells 30 have obtained a crystalline compound 3Ca0,A1,0,,3Ca0,Si0,,3Q-32H20 from pure cement compounds immersed in a saturated lime solution. The hydrated calcium aluminates and ferrites form a complex series of but the manner of the hydration of 3CaO,A1,0 and 4Ca0,A1,0,,Fe20 in Portland cement is controlled by the presence of the gypsum added. Calcium sulphate forms two double salts with tricalcium aluminate having hexagonal or pseudo-hexagonal symmetry and represented by the formulze 3Ca0,A1,0,,3CaS0,,32H20 and 3CaO,A1,O3,CaS0,,12H,0.Corresponding sulphoferrites are also known to exist. The compound 3Ca0,A1,0,,3CaS0,,32H20 is probably formed initially in the hydration of Portland cement but this is not the final end-product for it may be trans- formed 31 into a solid solution of 3CaO,A1,O3,CaS0,,12H,O with the com- pound 4Ca0,A1,0,,13H20. The latter arises from the hydration of 3CaO,A1,0 in the cement surplus to that with which the gypsum can combine. The close analogy between the calcium sulphoaluminates and aluminosilicates also suggests the possible existence of a calcium sulpho- aluminosilicate or of solid solutions. The subject is however even more complex for there also exists a compound 3Ca0,A1,0,,6H20 which belongs to the cubic system and is related in structure to the garnet series.The sulphate-containing solid solution mentioned above and possibly also the compound 4CaO,~,0,,13H2O are metastable with respect t o it at room temperature. A complete series of hydrogarnet solid solutions 32 of the general formula.? 3Ca0,A1,03 6H,0-3Ca0,A1,0,,3Si0 3Ca0,Fe,03,6H,0-3Ca0,Fo,0, 3Si0 I I are formed at high temperatures and steam pressures and there is some evidence to suggest that they may eventually be formed at normal temperatures. It will be evident that although the initial hydration products of Portland cement at normal temperatures are probably Ca(OH),,2Ca0,Si02,aq. or 3CaO,2SiO2,aq. 3CaO,A1,O3,3CaS0,,32H,O 4CaO,Al2O3,13K,O and an uncertain iron compound yet these do not represent the final chemical equilibrium in the multi-component system involved. In such systems however the final equilibria may not be attained for many years if indeed it is ever reached within the life of man. 30 J . Res. Na,t. Bur. Stand. 1944 33 471. 31F. E. Jones J . Physical Chem. 1944 48 311; 1945 49 344. H. P. Flint H. F. McMurdie and L. S . Wells J. Res. V a t . BUT. Stand. 1941 26 13.

ISSN:0009-2681    

DOI:10.1039/QR9490300082

出版商:RSC    

年代:1949

数据来源: RSC

摘要:

INDEX T O V O L . 111 INDEX T O V O L . 111 Authors of Articles :- Atherton F. R. some aspects of the organic chemistry of derivatives of phosphorus oxyacids 146 Sarrer R. M. molecular-sieve action of solids 293 Barton D. H. R. the chemistry of the diterpenoids 36 Bockris J. O’M. ionic solvation 173 Bolland J. L. kinetics of olefin oxida- tion 1 Crawford V. A. hyperconjugation 22G De la Mars P. B. D. kinetics of thermal addition of halogens t o organic com- pounds 126 Elcy D. D. mechanisms of hydrogen catalysis 209 Gibson D. T. the terrestrial clistribu- tion of the elements 263 Hickling A. the mechanism of electrode processes in aqueous solutions 96 Lea F. M. the constitution of Portland cement 82 Leech H. R. laboratory and technical production of fluorine and its com- pounds 22 Lythgoe B.some aspects of pyrimidine and purine chemistry 181 Nyholm R. S. recent stereochemistry of the Group VIII elements 321 Percival E. G. V. carbohydrate sul- phates 369 Riley H. I,. carbides nitrides imd carbonitrides of iron 160 Stnveley 1,. A. I<. transitions in solids and liquids 65 Synge R. L. M. naturally-occurring peptides 245 Topley B. hhecondensedphosphates,345 Abietic acid structure of 37 38 rbeoAbiotic acid 44 Acetylene exchange reactions of 222 hydrogenation of 224 6-Arctrylornithjne 266 Adanine synthesis of. 192 Adenosine 183 ddrenocorticotrophiri 2.j4 ,2Grosporin 260 ,%gar-agar 378 dgtlthenedicarboxylie acid structure of isoAgathenedicarboxylic acid 60 Alcohols diterpenoid 52 Alga marine polysaccharide sulphat es of 37,49 376 Slkylbenzenes absorption spectra and ionisation potentials of 238 INDEX 1949 387 Alkyletlylenes absorption spectra a,nd Alkylpyrimidines 198 2-Alkylthiopyrimidines 200 Alloys order-disorder in 68 Alternating-current methods 100 L4hxminium carbonitride 168 oxide 281 Amanitine 258 Ambrein 63 Aminopyrimidines 20 1 Ammonium halides transitions in 74 Anionotropy 242 Anodes carbon 26 *hserine 255 Antibiotics 262 ,4ntimalarials 182 L4ntioxidants phenolic 9 Arsine complexes 341 Atmophil 264 Atmosphere 277 Autoxidation 6 ionisation potentials of 237 Bacitracin 261 Bacteria peptides from 258 Barbituric acid structure of P O 3 Benzene exchange reactions of %2 1 Benzoyl peroxide oxidation catalysis by 6 Biosynthesis 184 185 Bistriethylphosphinedibromonickel 333 Bond length hyperconjugation and 232 Bond orbitals shape of 326 Bond orders 231 ,€!-Brass 69 Bromide ions catalysis of bromine addi- Bromine addition of catalysed by halide hydrogenation of 224 tion by 136 ions 135 fourth order 134 third order 130 Calcite effect of phosphates on precipita- Calrium alumintttes !X tion of 367 ferrites 93 oxide 283 silicates 88 Camphorene 68 Carbohydrate sulphetes 369 alkaline hydrolysis of 370 animal 381 natural 375 and oxides 162 Carbon monoxide reaction of with metals tetrafluoride 33 Carbonitrides 168 Carbonitriding 167 388 INDEX Carhnyl compounds reactions of with Carnosine 256 Carragheenin 376 Casein phosphopeptones 251 Catalysis hydrogen mechanism of 20‘3 Catira tree resin from 51 Cativic acid 51 Cells electrochemical fluorine 22 Cement Portland constitution of 82 Chalcophil 264 Charcoal molecular-sieve action in d97 G‘hemisorption theory of 210 Chloride ions catalysis of‘ broinuio addi- Chlorine fluorides 35 Chondroitin sulphate 381 Clupein 253 Cobalt complexes 330 334 335 337 Complex - ion for mat ion 3 63 Compressibility ionic solvation and 179 G‘o-ordination numbers of Group VIII Uopal Kauri and Manila resin acid from Cytidine 183 Cytosine synthesis of 187 197 Deuterium halides transitions in 79 phosphorus trichloride 157 tion by 135 elements 322 326 333 334 49 synthesis of 190 overpotential of 11 1 separation from hydrogen 3 1 1 Deuteromethanes transitions in 78 Dextropimaric acid structure of 37 45 GoDextropimaric acid 48 Diazomethane reaction of with dialkyl fluorophosphonates 156 Dienes cyclic absorption spectra and ionisation potentials of 239 Dihydrodextropimaric acid 47 Dihydrosclareol 53 DiEsea edulis galactan sulphate from 378 Dimethylglyoxime complexes 335 Dimethylcyclohexane peduoro- 34 Dipole moments hyperconjugation and Diterpenoitls chemistry of 36 Earth elements in crust of 266 Elastomers diffusion through 314 Electrodeprocessesin aqueous solutions 95 Electrolytic oxidation 120 Elements Group VIII stereochernistry of 234 reduction 120 32 1 terrestrial distribution of 263 Elimination reactions 244 Entropy ionic solvation and 178 Erdmann’s salt 337 Ergobasine 257 Ergocornine 257 Ergot alkaloids 257 .Ethylenediarniiie coiqdexes 339 Exchange reactions 2 19 Ferruginol 56 Fichtelite 60 Films chemisorbecl 609 Fluorides as fluorine carriers 31 35 Fluorine cells 22 handling of 31 laboratory and technical production of 22 Fluorocarbons 34 Yossil rosins 37 Freons 33 E’ucoidin 380 Fungi peptides from 256 (>alactitn sulphate 378 Galactose sulphates 370 Gases diffusion of through metals 309 through organic membranes 314 through silica glass 312 Germane transitions in 78 Glucose sulphates 370 3-Glucosidouritcil 190 Glutathione 254 Gramicidins 258 Guanosine 183 Halogen acids catalysis of hamlogen addi- Halogenophosphonates.149 Halogenopyrimidines 199 Halogens addition of 243 nucleophilic 138 table of rates of in acetic acid 145 to olefins 126 tion by 140 Heats of hydrogenation 236 Heparin 383 Hinokiol 57 Hippuric acid 256 Homoretene 38 Hormones pituitary 254 Hydrocarbons diterpenoid 58 Hydrogen atoms exchange reactions of separation of by sorbents 307 216 bromide transitions in 80 cathodic evolution of 107 chemisorption of 209 chloride transition in 79 deuteride formation of 216 fluoride anhydrous 33 overpotential of 11 1 separation from deuterium 3 1 1 pam-Hydrogen conversion 214 Hydrogenation 222 Hydroperoxides 2 decomposition of 16 Hydroxypyrimidines 200 Hyperconjugation 226 Hypertensin 251 Hypophosphoric acid 348 Ethylene chemisorption of 2 13 exchange reactions of 2 19 hydrogenation of 223 Intracrystalline sorption 2 9 S Ionic mobility 177 INDEX Ionisation potentials hyperconjuption Iridium complexes 335 Iron carbides 161 carbonitrides 167 compounds electronic arrangement of nitrides 166 oxides 282 reaction of wit#h carbon monoxide 163 and 237 32 3 Tsotopes separation of 3 11 Kaurene 59 Ketomanoyl oxide 54 Kurrol salt 357 Lactotyrines 251 Levopimaric acid 42 Licheniformin 261 Liquids transitions in 65 Lithophil 264 Lycomarasmin 257 Maddrell salt 355 Magnesium oxide 283 Manganese oxides 282 Manool 54 Manoyl oxide 54 Marrubiin 60 Membranes molecular-sieve properties of 309 organic molecular-sieve properties of 314 transmitting ions 318 Mercaptopyrimidines 199 Metals cathodic deposition and anodic dissolution of 123 Methane transitions in 78 Methylabietin 38 Micro-organisms requiring purines and Minerals molecules occluded or excluded Miro tree resin from 61 56 Miropinic acid 51 isoMiropinic acid 5 1 Molecular-sieve action 293 in solution 317 separations by 307 transmission of gases through 309 pyrimidines 186 by 304 Molecules planar configuration 327 Monolayers mixed 213 Monosaccharide sulphates 370 Mucoitin snlphate 383 Nickel chemisorption on 212 Kiobium carbonitride 169 Nitriding 167 Nitropyrimidines 199 Non-metals weathering of 285 isoNoragathenecarbosylic acid 50 isoNoragatheno1 50 Nucleic acids relation of to purines and pyrimidines 183 tetrahedral configuration 331 vomplexes 329 330 331 333 336 Nucleosides 183 Nuclcotides 183 Ocean 278 Olefin oxideg reaction of with phosphorus Olefinic compounds halogen additmion to Olefins kinetics of oxidation of 1 trichloride 159 126 third order addition of bromine to 130 Oleoresins acids from 37 Ornithuric acid 256 Orotic acid 181 Osmium tetroxide 332 Overpotential activation 104 concentration 102 deuterium 11 1 hydrogen 107 metal deposition 124 oxygen 1 16 Oxidation of olefins 1 Oxides mixed phase equilibria in 85 Oxygen anodic evolution of 1 1 :? chemisorption of 2 12 overpotential of 11 6 Palladium complexes 329 33 1 Palladous chloride 340 Paludrine 182 Pantothenic acid 255 " Paritol " coagulation inhibitor 384 Pegmatites weathering of 289 Penicillins 256 Pepsitensin 251 Pep tides naturally - oc curr ing 2 4 5 Perchloric acid catalysis of halogen addi- Perfluorobenzene 34 Peroxides 2 Phalloidine 258 Phase equilibria in mixed oxides 85 Phenols diterpenoid 52 Phosphates condensed 345 surface effects of 367 structural formulz 347 Phosphine complexes 341 Phosphonates 150 Phosphoric anhydride 345 Phosphorus chlorides 155 157 esters 151 153 halides reactions with 152 1 iydroxy-compound s 147 osyacids organic derivatives of 146 tion by 138 decomposition of 16 Photo -oxidation 6 Phyllocladene 59 isoPhyllocladene 59 Physiological action of peptides 249 Phytol 5% Pimanthrene structure of 37 Pituitary hormones 264 Platinum complexes 328 330 334 338 Podocarpic acid 50 Podocarpinal methyl ether 61 342 390 INDEX Podocarpinol methyl ether 51 or-Podocarprene 59 S-Podocarprenc.59 Poisons catalytic in electrode processes Polarisation and electrode kinetics 101 Polishing electrolytic 125 Polymerisation anionic in anodic oxida- Polymyxins 260 Polynuclear complexes 339 Polyphosphates 360 Polysaccharide sulphates 376 Potash 284 Potentials polarisation decay rate of 99 Propagation processes 12 Protamines 252 Proteins peptides as models for 246 Prototropy 242 Pteridine 18 1 Pteroic acid 255 Purine nucleosides 19 1 Pnrines chemistry of 18 1 Pyrimidine chemistry of 18 1 111 concentration 101 tion 121 growth rate of 97 synthesis of 191 nucleosides 190 synthesis of 187 Pyrimidines chemistry of 194 Quinazoline 181 Qizinol as antioxidant 9 Reactions at working electrodes 96 Refractivity molecular hyperconjugation Resin acids diterpenoid 37 Retene structure of 37 Rhodium complexes 335 312 Rimu tree 60 Rimuene 59 Rocks igneous 264 metamorphic 265 sedimentary 264 and 240 Rosins fossil 37 Rubber vulcanisates hydrocarhon dif- Ruthenium complexes 330 fusion through 315 tetroxide 332 Salmine 253 Sclareol 53 Secretin 254 Siderophil 264 Silica glass diffusion of gases through 312 Silicane transitions in 78 Silicate melts phase equilibria in 8.5 Silicon dioxide 281 Soda 284 Sodalite 299 Sodium ions hydration number of 175 metaphosphate 349 glass 358 insoluble 355 357 Sodium phosphates condensed nomen- clature of 351 polymorphism of 350 tetrametaphosphate 353 trimetaphosphate 35 1 triphosphate 360 transitions in 65 solids 317 numbers table of 180 tion in 143 Solids molecular-sieve action of 293 Solutions transmission of ions of through Solvation ionic 173 Solvents non - hydroxylic ha1 ogen R d Cl i - Solvent transport 176 Sorbents poroiis molecular-sieve action Spectra absorption hyperconjugation Steel case-hardening of 167 Stereochemistry of diterpenoids 60 in 293 and 237 of Group VIII elemenhs 321 theory of 323 Strepogenin 252 Siibtilins 261 Sugiol 58 Sulphadiazine 152 Siilphamethazine synthesis of 190 Sulphur hexafluoride 34 Sulphuric acid ctttalysic; of hnlogen addition by 138 Tetralin oxidation of 20 21 Tetramethylplat,inum 339 Thyrotrophin 254 Totara tree wood of 58 Totarol 58 1 7 8-Trimethylphennnthrene st nicture of 37 Triterpenoids 63 Tuberculin 26% Tporidines 259 'l'yrotlu-irbin 25% Unsaturated Compounds exchange and hydrogenation of 2 19 hyperconjugation in 230 Uracil spectrum and structure of.205 Uridine 183 Valency of Group VIII elements 332 Vasicine 18 1 Velocity of elementary reactions 10 Vitamin-B, synthesis of. I97 Vitamin-B and -B2 181 Voltammetry 96 Voumapenic acid 3 2 Weathering 279 Xanthosine 194 Zeolites %93 298 grouping of 302 intracrystalline diffiisinn in 3 12

ISSN:0009-2681    

DOI:10.1039/QR9490300385

出版商:RSC    

年代:1949

数据来源: RSC