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Proceedings of the Chemical Society, Vol. 13, No. 186 |
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Proceedings of the Chemical Society, London,
Volume 13,
Issue 186,
1897,
Page 235-250
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摘要:
PROCEEDINGS OF THE CHEMICAL SOCIETY. EDITED BY THE SECRETARIES. No. 186. Session 1897-8. December 15th, 1897. Extra Meeting. Professor Dewar, F.R.S., President, in the Chair. Professor F. R. JAPP,LL.D., F.R.S., delivered the Kekul6 Memorial Lecture. Friedrich August Kekul6 was born at Darmstadt on September 7th, 1829. Originally intended for the profession of an architect, he was induced, by hearing Liebig’s lectures, to devote himself to chemistry. After studying under Liebig, he spent a year in Paris, where he became intimate with Gerhardt. Later on, he resided for a time in London, making the acquaintance of Williamson and Odling. He always acknowledged the influence which these three chemists had exercised on the formation of his opinions.Kekulk’s theories are based on Gerhardt’s type theory ; on Williamson’s theory of polyvalent radicles, which, by their power of linking together other radicles, render possible the existence of multiple types ;and on Odling’s theory of mixed types, which was a deduction from Williamson’s theory. Less consciously, perhaps, his opinions were influenced by E. Frank-land’s theory of the valency of elementary atoms, and by Kolbe’s speculations on the constitution of organic compounds. Kekule gathered together the various ideas which he found scattered through- out the writings of his predecessors, added to them, and welded the whole into the consistent system which forms our present theory of chemical structure. In 1557, in the course of a memoir on the con- stitution of fulminic acid, he gave a tabular arrangement of compounds formulated on the type of marsh gas, this being the earliest statement, although put forward only in an imperfect form, of the tetravalency ofcarbon.In the same year, he published an important theoretical paper : ‘‘On the so-called Conjugated Compounds and the Tlieory of Polyatomic Radicles,” which contains a complete system of mu1 tiple types and mixed types. In 1858, the celebrated paper, “On the Constitution and Metamorphoses of C‘hemical Compounds, and on the Chemical Nature of Carbon,” appeared; it embodies the fully de- veloped doctrine of the tetravalency of carbon, together with Kekule’s views on the linking of atoms and on the valency of such chains of atoms-the foundation on which our modern system of constitutional formulae rests.In 1865, Kekul6 put forward his well-known benzene theory-the crowning achievement;, in his hands, of the doctrine of the linking of atoms, and the most brilliant piece of scientific prediction to be found in the whole range of organic chemistry. The conception of closed chains, or cycloids, which he thus introduced has shown itself to be capable of boundless expansion. Kekuld published the first instalment of his Lehrbuch dey o~ganischen Chemie in 1859. The work was never finished; but it was instru- mental in widely disseminating Kekuld’s views and exercised enormous influence on the development of the science. Kekuld obtained the uenia Zegendi in Chemistry at the University of Heidelberg in 1856.Two years later he was called, as ordinary pro- fessor, to the University of Ghent, where he remained until 1867, when he was appointed to the Professorship of Chemistry in the Uni- versity of Bonn, a post which he continued to hold until his death on July 13th, 1896. During his later years he suffered from bad health. The characteristic note of Kekule’s great theoretical creation, the chemistry of structure, is the treatment of the problem of isomerism -the problem which first necessitated the use of constitutional for mulae-as one of geometrical symmetry. Kekulh’s formulae, freed from the fetters of the type theory with which he at first encumbered them, were merely more or less symmetrical geometrical figures. In order to predict the number of substitution compounds, it was only necessary to consider the degree of dissymmetry of the parent com- pound : the less the symmetry, the greater the number of isomeric substitution compounds. The extraordinary fertility of this concep- tion is shown by the development which it has undergone at the hands of van’t Hoff, J.Wislicenus, von Baeyer, and others. The accuracy of Kekule’s predictions has doue more to inspire ;t belief in the utility of legitimate hypdheses in chemistry, and has therefore done more for the deductive side of the science than that of almost any other investigator. His work stands pre-eminent as an example of the power of ideas. A benzene formula, consisting of n few chemical symbols jotted down on paper and joined together by lines, has supplied work and inspiration for scientific organic cbemists during an entire generation, and affords guidance to the most complex industry the world has yet seen. Dr.HUGOMULLER,as probably the oldest personal friend of Kekul6 present, moved a cordial vote of thanks to Professor Japp for his elo- quent lecture, and added his special appreciation of the admirable and exhaustive manner in which the lecturer had accomplished his task. A considerable effort was needed to realise the condition in which organic chemistry stood fifty years ago, in order to recognise the vast advances which have been made in the interval. It may be truly claimed for Kekul6 that he holds a foremost position amongst those reformers who have initiated this progress.It was here, in London, that Kekule first conceived the ideas which, in their further develop- ment, assumed the shape of his “chemistry of carbon ” and (‘benzene kheory,” and>being in those days in almost daily intercourse with him, he well recollected the eagerness and enthusiasm with which the problems which occupied his mind were discussed. Soon afterwards, in Heidelberg,and then in Ghent, his affable manner and sociability attracted a number of devoted pupils, who became active fellow-workers, and thus his teaching bore fruit in all directions. Unfortunately, not long after he had been settled in Bonn, his health gradually gave way, and he suffered much from nervous prostration and an irksome degree of deafness, which at times much depressed him.His power of work became greatly impaired, and not- withstanding repeated heroic efforts, even his Handbook had to remain unfinished. Professor THORPE,in seconding the resolution, also desired to give expression to the sense of obligation which the Society was under to Professor Japp for the thoughtful and eminently impartial address which he had given. There-was, however, one slight but characteristic omis- sion in the lecture. In enumerating KekulB’s students, Dr. Japp had neglected to make any reference to himself. It was, no doubt, that same feeling of piety to which he had borne witness in the course of his lecture on the part of another which induced Dr.Japp to comply so readily as he had done with the request of the Council that he should undertake the weighty and responsible duty of delivering this address. His personal intercourse, as a student, with the master had, we may take it, quickened his appreciation of his work. At the same time, as would be evident, it had in no sense diminished his critical faculty. The audience had recognised that the lecture was a truthful and well-balanced account, written impartially and in the true spirit of history, of the origin and fruit, so far as this had been gathered, of the great chemist’s labours. Some reference had been made to the fact that he (the speaker) had enjoyed the good fortune of also being a student under Kekuld, and of being associated with him, in some small degree, in certain experi- mental work which he undertook during the first years of his professor- ship in the magnificent institution which Germany owes to Hofmann.It is a curious coincidence that Hofmann, like KekulB, might have become an architect, if destiny, as in Kekule’s case, had not intended that he should be a chemist. During the late sixties there was no sign of the decay in intellectual vigour which a few years later became so sadly obvious. At that time, the great generalisation which we associate with KekulB’s name was still, to some extent, on its trial, and it had to withstand the assaults which were from time to time delivered by keen and active opponents in other schools of chemical thought.It happened that very shortly after the speaker’s entrance into KekulB’s laboratory, he was called upon to handle the weapons which Kekule himself placed in his hands in order to defend a small, but apparently vulnerable point, in the theory. That circumstance proved of incal- culable benefit to him, in that it brought him into intimate personal contact with Kekulb, and enabled him to see something of his methods of work, and of the springs of his intellectual activity. Dr. Ja,pp has ably testified to Kekuld’s merits as a teacher. Kekuld, indeed, was one of the very best expositors, with the single possible exception of Kirchhoff to whom it had been the speaker’s lot to listen. As a laboratory teacher he was excellent.He was a most severe judge of work, striving to exact the same high manipulative finish, the same neatness and order, which he invariably bestowed on everything he did, and he was absolutely intolerant of anything slovenly or ‘sloppy.’ But it was as a lecturer that he was seen at his best. He was singularly luminous as a thinker, a close and accurate reasoner, with a remark-able power of concentrated expression. He was not a rapid speaker, and he never indulged in those rhetorical flights with which Hofmana occasionally was wont to electrify an audience. His language was apt and well chosen, and his delivery easy and natural. His lecture-table was never overburdened with ‘experiments ’; those he showed were strictly proper to the subject in hand.To see him handle the chalk was in itself a liberal education. Although everything appeared to be so easy and natural, an attentive critic could hardly fail to perceive that the lecture had been carefully thought out beforehand, possibly over a longer period of time than it took to utter. Every detail would seem to have been considered, even to the particular places on the black-board where the formuls should appear. During the later period of his life, KekulB, unfortunately for Science, was comparatively sterile. Those who knew him, however, would be the first to affirm that this seeming apathy sprung from no natural indolence. There is no doubt that he suffered, even in the early period of middle life, from the intense stress and strain of his mental labours prior to the Ghent period.He had too surely exemplified the sad truth of Liebig’s saying, to which Dr. Japp had referred, that he who would become a great chemist must pay for his preeminence by the sacrifice of his health. There is reason to know that it was the consciousness of failing power which prevented him from finishing much to which he had put his hand, and that his fastidiousness and his sense of “finish,” amounting almost to hypercriticism, restrained him from publishing what he realised fell short of his ideal. What he has left us, however, is an imperishable monument to his genius. The PRESIDENTsaid that therejwas little to add to Professor Japp’s exhaustive eulogy of the life and work of KekulB .His own early relations, however, with the great chemist whose life work the Society was commemorating might have some interest to the members and ought fo be told. While a student with Lord Playfair at Edinburgh, in the session 1866-67, he made his first [contribution to Science in the shape of a little paper entitled, ‘‘On the Oxidation of Phenfl Alcohol and a Mechanical Arrangement adapted to Illustrate Structure in the Non-saturated Hydrocarbons.” This note appeared in the Proceedings of tlie RoyaE LJociety of Edinbwgh, and he was so desirous of becoming known to Kekulk as a studenbof his theory of the aromatic bodies that a specimen model was sent to Ghent. Lord Playfair addressed a letter to Kekulh stating that he (Professor Dewar) was very anxious to work in his laboratory.The reply was (‘Come,” and the reception and kindness he received from Eekulh has always had his profound gratitude. The summer of 1867 was thus spent in the private Iaboratory of XekulB. Before leaving Edinburgh, he had been working on the coal tar bases, and a supply was taken with him to Ghent. There he began the study of the oxidation products of picoline, and at the British Association Meeting at Norwich, in 1868, an account of the separa- tion of dicarbopyridinic acid, the analogue of phthalic acid in the benzene series, was given. At the same meeting, he gave a paper on “ KekulB’s Model to Illustrate Graphic Formulae.” This is the succinct history of the beginning of the pyridine-benzene analogy.His old friend, Koerner, had speculated in the same direction, and he (Prof. Dewar) might confess that in his opinion they both had received too much credit for an extension of the benzene theory to pyridine. At a distance of thirty years, to look back and call to mind the presence and personality of the great chemist as he knew him was indeed a pleasure. He was a man of noble mien, handsome, dignified, and yet of a homely and kindly dis- position. He was a severe critic, having a haughty contempt for the 240 accidental and bizawe in scientific work. His originality and sug- gestiveness seemed endless, so that he had no need to commit scientific trespass or to follow just in the wake of other people's ideas.Every-thing that passed through the KekulB alembic was indeed transmuted into pure gold. His precision of thought and diction rendered his papers profoundly suggestive to other workers. His great work wilI always live in the history of our Science, and his loving memory will be for ever enshrined in the hearts of his pupils. December 16th, 1897. Professor Dewar, F.R.S., President, in the Chair. Messrs. James C. Philip, Edward Rosling and Frank T. Addyman were formally admitted Fellows of the Society. The PRESIDENTannounced that the following had been recommended by Council for election as Foreign Members, to be balloted for at the next meeting, January 20th, 1898. Prof. Remsen, Baltimore, U.S. A.; Prof. Troost, Paris ; Prof. Moissan, Paris ; Prof.Raoult, Grenoble ; Prof. Ostwald, Leipzig ; Prof. Curtius, Bonn ; Prof. Mensutkin, St. Petersburg ; Prof. Markownikow, St. Petersburg ; Prof. Arrhenius, Stockholm ; Prof. Waage, Christiania ; Prof. Franchimont, Leyden ; Prof. van der Waals, Amsterdam ; Prof. Spring, Liege ; Prof. Korner, Milan. Certificates were read for the first time in favour of Messrs E. L. Allhusen, B.Sc., Geological Survey, Perth, W.A.; B. S. Bull, M.A., B.Sc., Ph.D., 49 Devonshire Road, Greenwich; T. H. Hills, 6 Eliot Park, Blackheath ; J. E. Miller, Holmoor, Patrington, Hull ; G. T. Morgan, 35A Russell Road, Kensington, W.; 14'. E. Moss, B.A., Burnthwaite, Bolton; H. Poole, 333, W. 34th Street, New York; W. Richards, Old Elvet, Durham. The following papers were read :-"126." Stereochemistry of unsaturated compounds. PartI. Esterifica-tion of substituted acrylic acids." By John J. Sudborough and Lorenzo L. Lloyd. In order to determine whether there is any general rule applying to the esterification of unsaturated acids, similar to those discovered by Mensutkin for fatty acids, and by Victor Meyer and Sudborough for aromatic acids, the authors hare investigated the following acids : cinnamic acid, allocinnamic acid, atropic acid, ortho-, meta-, and para-nitrocinnamic acids, a-bromocinnamic acid, a-bromallocinnamic acid, two P-bromocinnamic acids, two a-P-dibromocinnamic acids, a-/?-di-chlorcinnamic acid, a-P-di-iodocinnamic acid, a-cyanocinnamic acid, a-cyano-meta- and a-cyano-ortho-nitrocinnamic acid, a-phenylcinnamic 241 acid, a-phenylallocinaamic acid, six a-phenylnitrocinnamic acids, tri- phenylacrylic acid, a-6-di-iodoacrylic acid.Half a gram of aacb acid was boiled for an hour with 10 C.C. of a 3 per cent. solution of hydrogen chloride in methylic alcohol, and the amount of ester formed determined in the usual manner. The authors draw the following conclusions from the results which they have obtained :-(1) Unsaturated acids of the types, H(Y)C:C(X)CO,H and Z(Y)C:C(X)CO,H, yield but small amounts of ester when treated in the manner described. This furnishes a ready method for distinguishing stereoisomeric acids. (1) H(Y)C:C(X)CO,H and (2) H(Y)C:C(CO,H)X. As acids of the trans-type (1)are esterified with difficulty, and acids of the cis- type (2) with ease by the above method, it is probable that the method can also be used for separating mixtures of such acids, in very much the same manner that diortho-substituted benzoic acids can bs separated from their isomers.(2) An a-substituted acrylic acid, CO,HC(X):CH,, is more difficult to esterify than a &substituted acid, CO,HC(H):CHX. (3) In certain substituted cinnarnic acids, a nitro-group in the ortho- position appears to have a retarding influence. The results obtained, are completely in accord with those published by Anschiitz (Ber.,. 1897, 30,2652) whilst the present work was still being carried out. The constitution of camphoric acid is discussed in the light of the results contained in the paper.The authors think it desirable to carry out similar researches with substituted acids ; they have already found that dibromosuccinic acid, phenyldibromopropionic acid and its nitro-derivatives, yield but little ester when boiled for an hour with a 3 per cent. solution of hydrogen chloride in methylic alcohol. Several new methylic esters have been obtained, and are described in the paper. “127. “Formation and hydrolysis of esters.” By John J. Sudborough, Ph,D., D.Sc.,and Martin E. Feilmann, B Sc. From the researches of Mensutkin (Anmzlen, 1879, 195, 334, 1879, 197, 193) on the esterification of fatty acids, of Victor Meyer and Sudborough (Bey., 1894, 2’7, 510, 1580, 3146) on substituted benzoic acids, and of Sudborough and Lloyd (preceding abstract) and Anschiitz (Ber.,1897,30, 2662) on unsaturated acids, the authors con- sider it proved beyond doubt that stereochemical influences play a most important part in the esterification of an acid by means of an alcohol and hydrogen chloride.Researches by Kellas (2.physik. C?t,em.,1897, 242 25, 221) on the esterification of monosubstituted benzoic acids, and of Sell (Trans., 189’7, 71, 1070) on substituted pyridinecarboxylic acids also support the same conclusion. In the benzoic and acrylic acid series, the chemical nature of the substituting groups has but little, if any, influence on the retardation of esterification. CH,, F, C1, Br, I, NO,, OH and CO,H groups all act in the same manner ; the radicle weight or volume, however, affects the retardation to a certzuin extent (Meyer, Bey., 1895, 28,1259, and Kellas, Zoc.cit.). One would therefore conclude that in the fatty series, too, the chemical nature of the substituting groups would have but little, if any, apparent influence. A tertiary fatty acid, however, such as trimethylacetic acid, yields but little ester when heated with alcohol (Mensutkin), whilst the similarly constituted trichloracetic acid is most readily esteri- fied, in fact, much more readily than acetic, mono- or di-chloracetic acids (Lichty, Am. Chew. J., 1896, 18, 590). This difference in behaviour we can only attribute to the enormous increase in strength of the acid. K K (1) Acetic acid 0.0018 (3) Dichloracetic acid 5.14 (2) Chloracetic acid 0.155 (4) Trichloracetic acid 121.0 Lichty’s researches show that these four acids follow exactly the order given above as regards the ess3 with which they are esterified.The amounts of ester formed at the end of any given time by no means bear the same ratio to one another as do the affinity constants of the corresponding acids. After 1 min. 1 hour. 2 hours. Chloracetic ....,. 1.78 41.89 57.33 per cent. Dichloracetic ... 4.56 56.49 62.34 ,, Trichloracetic ... 9.99 59.39 66.18 ,, It would appear then that some other factor is introduced which tends to hinder the formation of the esters, and this factor the authors con- sider to be the stereochemical influence of the chlorine atoms. The general conclusion drawn is that in the conversion of an acid into its ester by the action of an alcohol, either with or without hydrogen chloride, the rate of esterification is determined by two factors :-1.The configura- tion of the acid, in other words, the presence of substituting groups situated close to the carboxylic group, which always tend to hinder esterification. 2. The strength of the acid as determined by its affinity constant. In most of the cases which have been more closely studied, the first factor is the more prominent, and obscures, to a largeextent, the influence of the second factor. In exceptional cases, however, namely, in acids the strength of which has been enormously increased, the second factor becomes the more prominent, and the influence of con 243 6guration is cloaked.In all cases, however, we must suppose the two factors to be in force, and it is only in acids which have the same affinity constant that the true effect of stereochemical influence can be looked for. No general systematic study of the rate of hydrolysis of esters appears to have been attempted. Victor Meyer (Ber., 1895,28,1263) formulated the generalisation that those esters which are the most *difficult to form are also the most difficult to hydrolyse. This view was also held by Wegscheider (Bey., 1895, 28,2536) and Bruhl, but according to the more recent investigations of Kellas, this generalisa- tion is not strictly correct. Kellas (Zoc. cit.) studied the rate of hydrolysis of the methyl salts of monosubstituted benzoic acids by means of alkali.He found that in any given series the ortho-com- pound is always the most difficult to hydrolyse, the para- occupies an intermediate position, and the meta- is most readily hydrolysed (with the exception of the nitro-compounds). It is stated, however, that methylic orthonitrobenzoate is much more readily hydrolysed than rnethylic orthotoluate, although the nitro-ester is formed much more slowly than the toluate. This and similar results noted by Kellas, for example, the fact that methylic benzoate is difficult to hydrolyse, can be accounted for by the introduction of the affinity of the acid as a factor. For orthouitrobenzoic acid K = 0,616, for orthotoluic acid K = 0.012, and for benzoic acid E = 0.006.The results obtained by Hjelt (Ber., 1896, 29, 1864) cn the hydrolysis of the ethylic salt of substituted malonic acids also lead to the same conclusion. They indicate that here, also, the rate of hydrolysis does not depend merely on the stereochemistry of the ester molecule. If the affinity constants are taken into consideration, the obstruction due to the substituting groups is much more pronounced (with the exception of ethylic allylmalonate). Investigations by the authors on the hydrolysis of the ethylic salts of acetic, methyl-, dimethyl-, and trimethylacetic acids by the aid of sodium hydroxide, prove that here, where the affinity constants of the acids vary but little-acetic acid IC = 0.0018 ; propionic acid K = 0.00134 ; isobutyric acid = 0.00144, and trimethylic acetic acid (unknown, but at any rate very small, since the salts of this acid are extremely unstable),-the rates of hydrolysis are what would be expected from the introduction of the substituting groups- Hours. 0'25 0'5 1 1.5 8.5 3 4 43 8 10 22.5 70 Ethylic acetate .............19.6 28 42 66 82 6 85'4 pergmt. ,, propionate ......... 14'4 19'6 33'6 50'8 61.2 I1 7, ,I isobutyrate......... 5'2 7'2 11'4 19.2 61 I> IS , , trimethylacetate 2'4 6'8 S.8 19.6 ,. ,, With the esters of chlorinated and brominated acetic acids, the reverse is true, and all are decomposed much more readily than ethylic acetate itself. Comparative experiments with these esters are being under- taken by the authors.The general conclusion arrived at is, therefore, that in the hydrolysis of esters by the aid of an alkali, the same two factors operate as in esterification. The strength of the acid which is formed by the hydrolysis of the ester seems, however, to play a moreimportant part than it did in esterification, and this accounts for the fact that it does not always follow that esters which are most readily formed are the most readily hydrolysed. Other factors are apparently introduced when esters are hydrolysed by the aid of hydrochloric acid, as it has been proved that esters by no means arrange themselves in the same order when hydrolysed by an alkali as when hydrolysed by an acid (Hemptinne, Z.physik. Chem., 1894, 13, 561 ;Liiwenherz, ibid., 1894, 15,389 ;Van Dyken, Rec.Z’v-av, Chim.,1895, 14, 106). The authors consider that these generalisations can be proved or refuted only by a much more careful study of the hydrolysis of numerous series of esters. They themselves intend investigating the ethylic salts of Substituted (alkylated) succinic acids, as the strengths of these acids differ but little, and therefore the results obtained should throw light upon the retarding effect of different alkylic groups. DISCUSSION. Dr. HEWITTsaid that the fact that hydroxylfluoronecarboxylic acid, m. O:C,H3/ \C,H,OH, yields scarcely any ethyl ester, even after \C-/CO,H prolonged boiling with 9 parts by weight of ethyl alcohol and 1 part of concentrated sulphuric acid, is easily explicable in the light of Dr.Sudborough’s work. Hydroxylfluoronecarboxylic acid is a tri-substituted acrylic acid, and hence should not easily esterify. On the other hand, Victor Meyer showed that triphenylacrylic acid, Ph,C:C( Ph)-CO,H, yielded an ester by prolonged boiling with methyl alcohol and a stream of hydrogen chloride. Under similar circum- stances, triphenylacetic acid, (C6H,),C0,H, furnished very little ester. Dr. SHIELDScalled attention to the numbers, quoted by the authors of the papers, representing the percentage amount of etherification after one minute, one hour, and two hours, and remarked that, whereas all the limiting values were approximately the same after sufficient time had elapsed, a considerable difference existed between the num- bers when the amount of transformation was measured after the lapse of only one minute.If it had been possible to obtain the correspond- ing values after one second, he thought the difference would have been still greater, and that in any serious attempt to study parallelism between the velocity of etherification and the affinity constants of the acids, it would be necessary to determine the relocity constant of the reaction or the initial rate of etherification. *128. “A new method of determining freezing points in very dilute solution.” By Meyer Wilderman, Ph.D. The chief condition for obtaining correct determinations of the freezing point is the establishment of equilibrium between the solid and the liquid part of the heterogeneous system.Starting from the properties of ‘‘perfect ” equilibripm, and from the equations for velocity of ice-melting, ice-separation, and Newton’s equation for cooling, all the conditions necessary for a successful experiment, pre- viously laid down empirically by the late P. B. Lewis and then by the author, are now deduced from theoretical considerations. It is shown how to arrange the equilibrium with an accuracy of 0~00002-0*00006° and even greater. The freezing point method, which has been hitherto a conglomeration of empirical rules, is thus placed on a physico-mathematical basis, and the experimental error of all previous methods can be calculated. The second important point in a freezing point method is a correct and very detailed knowledge of the registering instrument.X very careful study of the errors of mercury thermo- meters has been made for a long time, and an account of this is given. This paper is a continuation of that by P. B. Lewis (Trans., 1895, 67, 1). DISCUSSION. Mr, PICKERIKGexpressed his disappointment that the author had not made any statement as to what his ‘‘new method” was. All that he had given was a summary, in the form of an equation, of the various inaccuracies inherent in freezing point determinations generally. These inaccuracies were Fvell-known, and it was of great importance that they should be reduced to a minimum; but it was impossible to say whether the author’s new method succeeded in doing this or not until a description of the method was given.Dr. SHIELDSremarked that the literature and controversies on the vexed question of the accurate determination of the freezing point of dilute solutions would already fill a large volume. Since the subject was one of great importance in connection with the modern theory of solutions, any new contribution which was likely to lead to a final settlement of the conflicting views was welcome. He regretted that want of time had prevented Dr. Wilderman from giving a fuller ac- count of his papw, but the method of attack adopted by the author- was undoubtedly a step in the right direction, and he thought that the study of the time reaction and of equilibrium in freezing solutions would lead, if it had not already in Dr.Wilderman’s hands, led, to import- ant advances. Dr. WILDERMAN,in reply, stated that methods were given in the paper for obtaining the separated ice in fine films throughout the liquid. In answer to Mr. Pickering, he said that the value of the equations he laid down was that by them the errors due to equi- librium in the methods of other investigators could be estimated, and their -results recalculated. As an illustration, one of the most accurate of the recent methods was recalculated, and its error found to be 160 times greater than his own. He had presented, for the first time, the physico-mathematical theory of freezing point determinations in such a form that future experimenters could arrange with ease the equi- librium to any degree of accuracy required.++129.“A possible basis of generalisation of isomeric changes in organic compounds? By Arthur Lapworth, D.Sc. In this paper, the author points out that many isomeric changes, hitherto regarded as belonging to different types, may be formulated as special cases of a general form, which may be expressed by the reversible equation R,M*R&R,3 R,:R,*RiM, representing a labile group moving from an a-atom to a y-atom, the necessary rearrange- ment of single and double bindings taking place between the three atoms R,, Ra and R,. A conventional ‘‘mechanical ” representation of the change is given for the special case where R,, Rp and R, are carbon atoms. Examples, for the most part derived from “tautomeric” and ‘(desmotropic ” substances, such as acetoacetic ether, cyanic acid, nitroso-compounds, &c., are shown to be of the above type.Extensions of the above special form are deduced, and the general conclusion is arrived at, that in a chain of alternately singly and doubly-linked atoms, either (1) a labile group may become succes-sively attached to alternate atoms, or (2) an exchange of labile groups in y-(Le., meta) positions may occur. These deductions are shown to be confirmed by the behaviour of benzenoid compounds, &c., the fully justifiable assumption being made that benzenoid compounds may act as if possessing KekulB’s formula. Special reference is made to nitrophenol, orthohydroxyazobenzene, the sulphonic derivatives of aniline and of /3-naphthol, and also to the changes of methylaniline into paratoluidine and of hydrazobenzene into benzidine, which are all shown to exhibit changes in complete accordance with the author’s vie\rvs.247 Further modification of tho general formula for the case where Ra and Ryare singly, instead of doubly, linked, is shown to lead to the form R,M*R,=R, 2 R,:R, +R;M, which represents on the one hand the great majority of simple molecular decompositions of organic compounds, and on the other the formation of the ordinary addition products from unsaturated substances. The production of substitution derivatives, &c., by successive addition and isomeric change (compare Armstrong, Trans., 1887, 51, 258), as well as some simple cases of hydrolysis, are then discussed.From the last formnla, the following type is shown to be at once derivable : R; M +R,*R, 2 R;R, +R,M, which represents the ordinary process of substitution in saturated compounds [compare Armstrong, Zoc. cit., and Williamson (“ Theory of Etherification,” ISSl)]. With the help of the foregoing principles, the author shows that the production of meta-di-deriva tives from certain mono-derivatives of benzene may be consistently explained on the basis of Armstrong’s suggestion (Zoc. cit.) that in such mono-derivatives addition of the acting agent to the side group precedes substitution. Further, this assumption at once explains the replacement (by a substituting group) of side groups, which otherwise afford meta-derivatives. Some apparent exceptions to the foregoing principle are next dealt with, and it is shown that little difficulty exists in relegating to the above type the production of, for example, pinacolines from pinacones, acetanilide from acetophenone-oxime, benzilic acid from bend, &c., on suppositions which, for the most part, the author has not been the first to make, and which mostly involve the intermediate production of ring-compounds.It is further shown that the following type of change is possibly, but by no means necessarily, independent of the above, viz., R,M*REt,3R,:R,M (where Ra represents an atom possessing a ‘‘re-sidual affinity ” of two units), and a possible method of harmonising this with the other type is discussed in detail.Finally, it is pointed out that, although a brief dissociation between. the Iabile group and its attached atom must be assumed in order to. account for the above changes, caqes involving electrolytic dissociation or partial destruction of the labile substance necessarily involve pro- bable changes other than an ay-isomeric change, and should therefore be as far as possible avoided in investigating the applicability of the foregoing generalisation. DISCUSSION. Dr. WYNNEregretted that the author, in reuling his paper, had thought it more important to enumerat3 the varioiis well-known cases of tautomerism, than to give the explanation he had devised to account for this property.So far as could be gathered, the author sought to connect those reactions in which a single radicle is trans-ferred from one to the other of positions relatively 1:3 accompanied by a change of structure in the chain, with those in which mutual exchange of radicles in positions relatively 1:3 is brought about without any structural rearrangement. It was difficult to see wherein the analogy lay, but even iF the author’s contention were adopted, it was open to question whether anything had been thereby gained. The usual statement that ortho-, or para-, or both di-deriva- tives result from cornpounds of the phenylsulphamic acid type expressed the facts at least as clearly as the author’s emendation, wherein the reaction is represented as being brought about by the radicle moving from any given position to the next but one.What was to be desired was an explanation of the cause of the mutual transference, mot a re-statement of the fact of its occurrence. The author’s view of the formation of metanitrobenzene-sulphonic acid surely needed more explanation than the reaction for which it was put forward to account, and the same might be said of the argu- ments brought forward to explain the production of metasulphonic acids from aniline derivatives. A striking case of the production of such acids is exhibited by dimethylaniline, which with ordinary sul-phuric acid gives the para-, whilst with fuming sulphuric acid, a mixture of the meta- and para-sulphonic acids is obtained. Yet, according to .the author’s views, the meta-sulphonic acid should be the sole product in either case, since he considers that compounds of the phenylsulphamic acid type-which dimethylaniline cannot form-give rise to parasul- phonic, and compounds of the aniline hydrogen sulphate type-which dimethylaniline can form-give rise to metasulphonic acids.Again, the order in which isomeric sulphonic acids seem to be formed in the case of /3-naphthol had beenadduced by the author in support, of his views, but it was not difficult to quotecasesin which it appeared to be inapplicable. Erdmann had shown that 1:4-,1:4’-,and 1:3’-a-naphthylaminesulphonic acids are the products of the sulphonation of a-naphthylamine, and it was not easy to see how the production of the last named and most stable of these acids could be accounted for by the author, even if his views did not beg the question of the mode in which isomeric sulphonic acids are formed, as reference to Erdmann’s paper mould show.He was, moreover, unable to follow the author in tracing an analogy between the changes involving the production of ethylene from ethyl bromide, and of ethyl bromide from ethylene on the one hand, and those occurring in tautomeric compounds on the other; an analogy, $hat is, between reactions involving scission of the chain, and those in which none occurs. Markownikow’s rule embraced what is known of such reactions, and the author’s re-statement of some of the facts did not seem to add to, or explain, that well known summary. Professor COLLIEsaid that this generalisation of Dr.Lapworth’s appeared to him to be one of great importance. Any simple rule that would explain not only all cases of isomeric change amongst paraffinoid as well as amongst benzenoid derivatives, but also the hydrolysis of esters, the decomposition of diazo-compounds, the formation of meta- derivatives, &c., &c., mas one which certainly claimed the attention of chemists. Moreover, it received much support from a stereochemical point of view ; and if Dr. Lapworth’s first equation be allowed, then the rest of the argument was a clearly worked out, logical deduction. Dr. KIPPINQagreed with the last speaker, that the paper under discussion was one of great interest and importance.Starting from a simple case of tautomeric change, by an ingenious and logical applica- cation of views already widely accepted, Dr. Lapworth had attempted to account for, and to bring into line, a very large number of cases of isomeric change, which before seemed to be complex, obscure, and not related to one another in any way. If this generalisation were possible, as it certainly seemed to be from the formulae and explanations which Dr. Lapworth had advanced, his paper deserved, and would no doubt receive, the careful consideration of chemists. Mr. A. G. BLOXAMasked whether, in the event of such tautomerism as that referred to by Dr. Lapworth occurring in di-substitution products, the second group would exert any preventive action on the wandering of the first group.Thus, supposing that a sulphonic group tended to wander into the next following y-position, which, however, was already occupied by another group, would such a state of affairs determine the non-existence of a tautomeric form ‘1 Dr. LAPWORTH,in replying, regretted that the time at his disposal had prevented him from saying all he had wished. He had tried, in the first instance, to show that a great rrany isomeric changes, includ- ing those of elimination of two groups attached to contiguous carbon atoms and also of most changes in benzenoid compounds, might be written in a form derived from that representing the relationship between the two forms of simple tautomeric substances, and had shown in the paper that they might be represented on exactly similar stereo- chemical bases.The latter he had omitted to give in reading, as it involved the introduction o€the usual hypothetical space-relationships of carbon atoms and the idea of dissociation as distinct from decom- position, whilst the paper intended to call attention to what appeared to be a general type of change, logically deducible from a well-known form. With regard to the production of benzenoid substitution-derivatives, 250 he had already pointed out that, as a rule, where substitution in the benzene nucleus undoubtedly occurs, ortho- and para-derivatives are the chief products, and that this fact, as also the question of the stability of a particular benzene derivative, must depend on some principle not intimately connected with the mechanism of isomeric change.A change, analogous to that of compounds of the aniline hydrogen sulphats type would afford meta-derivatives, and evidence of this is afforded by the production of metanitraniline when aniline nitrate is treated with cold sulphuric acid ;the production of ortho- and para-derivatives may then be due either to direct substitution in the ,ring, or to isomeric change of compounds of the pheoylsulphamic acid or methylaniline type. Hence the formation of any particular acid from aniline, dimethylaniline, a-and P-naphthylamines, &c., is not difficult to account for, although the exact details of the production, or any one of them, would require a special discussion. The convenience of employing the above formula and the apparently very general applicability of the type of change to which the author desired to draw attention, would only be understood when it was applied to cases which, as the author shows in his paper, are difficult to discuss on the usual bases. In reply to Mr. Bloxam, the author said that the paper dealt with cases in which the y-position was already occupied, and in the special case alluded to, the author’s view made it clear that no entirely pre-ventive action would be exercised,and this would appear to be in accordance with known cases. At the next meeting, January 20th, 1898, there will be a ballot for the election of Foreign Members. RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.
ISSN:0369-8718
DOI:10.1039/PL8971300235
出版商:RSC
年代:1897
数据来源: RSC
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