camphorenic acid with sulphuric acid (Forster, loc. cit.) was found to be the most suitable substance for the purpose. It is rapidly attacked by a solution of silver nitrate in dilute nitric acid (1 vol. of nitric acid of sp. gr. 1.42, and 1 vols. of water), and if the mixture is heated on the water-bath for about 60 hours, homocamphoronic acid, sometimes amounting to more than 60 per cent. of the bromocampholid used, may be readily obtained. In this case also, the resulting homocamphoronic acid seems to be practically pure, and only very small quantities of any secondary products are present. A minute quantity of an acid which did not yield an anhydride when heated at 180° was observed, but the amount was less than 1 per cent. of that of the homocamphoronic acid obtained. Constitution of Bromocamphorenic Acid. Sufficient is now known of the properties of bromocamphorenic acid and its derivatives to warrant a discussion of the probable structural formula of this substance. It has been shown by Forster that the acid is unsaturated and that it contains one closed chain (loc. cit.). It is practically certain, moreover, that the grouping CH:CBr forms a portion of the closed chain, as the substance, when treated with icecold permanganate, rapidly loses bromine, and is subsequently converted into homocamphoronic acid, an open-chain tricarboxylic acid. This view represents the oxidation as resulting in the conversion of an CBr acid COOH CH13 into COOH-C-H13 COOH COOH and the fact that bromine is at once eliminated receives explanation in the circumstance that the glycol produced as the first step in the oxidation would contain the radicle >CBr OH, from which hydrogen bromide would be split off immediately with formation of the >CO group. This also supplies a simple explanation of the fact, among others, that a-monobromocampholid, when hydrolysed, yields an acid having the formula C10H1603 (Forster, loc. cit.). It was at one time thought possible that homocamphoronic acid might be formed from an intermediate B-ketonic acid by hydrolysis, but a number of important considerations have led to the rejection of this view. Of the formulæ containing the radicle CH:CBr, which can be devised to represent bromocamphorenic acid, in view of its simple relationship to homocamphoronic acid, only two, CBr CMe CH CMe.COOH 2 I. CH2 CMe2 CH CMe COOH, II. correspond in any simple way with any possible formula for a-dibromocamphor. These, moreover, are the only expressions containing in addition the group :CMe COOH, which is almost certainly present in bromocamphorenic acid for the following reasons. It is now scarcely open to question that camphoric acid contains the complex :CCCM-COOH present in camphononic acid, and consequently there are only three expressions possible for that substance, namely, the Bredt, Perkin, and Perkin-Bouveault formulæ. No matter which of these be the correct one, it must be supposed that :C-CH-CH2 , in which the transposi camphor contains the group tion of the CH and CO groups is not possible (compare Noyes, Ber., 1899, 32, 2289 and 2290). a-Dibromocamphor must therefore :C-CH-CBr, contain the group (compare Lowry, Trans., 1898, 73, 569, 1001). In its transformation into bromocamphorenic acid, it is at least certain that the CO∙ group is converted into COOH, and from what has been said it must be clear that separation of the •CO and CBr2 groups has occurred. Although some curious alteration in the structure of the molecule occurs, consisting evidently of the absorption into a ring of the carbon to which the bromine atoms are attached, it is altogether unnecessary to imagine that the change has extended to the group CMe CO, which, it is worthy of note, is present in homocamphoronic acid. We have now to choose between the formulæ I and II, and there can be little doubt which of these is to be preferred. The latter represents a yo-unsaturated acid, and in all probability an acid of this formula would be readily converted into the corresponding By- or aß-acid, whilst such an occurrence is impossible with an acid represented by formula I. There are, morever, a large number of facts which, taken together, speak in favour of formula I as against formula II. Thus in the expressions for a-monobromocampholid and for camphononic acid derived from formula II, namely: there is apparently no reason why oxidation should not take place at the points marked (b) as well as at those marked (a), whereas in fact only one product in each case can be isolated. All these difficulties disappear when formula I is used, and this expression explains in a most satisfactory manner all the facts bearing on the question which have been observed by Forster and by the author. It is difficult to understand the change which a-dibromocamphor undergoes in its conversion into bromocamphorenic acid, but it does. not become easier if any of the other possible formulæ for the latter substance be employed. The enlargement of a ring of carbon atoms by the inclusion of a carbon atom hitherto outside the ring is by no means an unknown phenomenon, and an assumption very similar to the one employed here, has been recently put forward by Wagner and Brickner to explain the conversion of pinene into derivatives of camphene (Ber., 1899, 32, 2323). It is worthy of remark that the formula above suggested as the most suitable for bromocamphorenic acid bears to Bredt's formula for dibromocamphor a relationship which could not, in the circumstances, be more simple. This relationship, as well as that connecting a number of important compounds the properties of which have necessarily been considered in eliminating the improbable formulæ, is exhibited in the following scheme : It is hoped that the investigation, which is still being carried on, may elicit further evidence bearing on the question discussed in the paper. Much of the expense incurred during the work has been defrayed by a grant from the Research Fund of the Chemical Society, and for this help the author desires to express his indebtedness. CHEMICAL DEPARTMENT, SCHOOL OF PHARMACY, 17, BLOOMSBURY SQUARE, W.C. CXVII.-Camphoroxime. Part III. Behaviour of Camphoroxime towards Potassium Hypobromite. By MARTIN ONSLOW FORSTER, Ph.D., D.Sc. On the failure of an attempt to prepare a-bromocamphoroxime by the direct action of bromine on camphoroxime dissolved in glacial acetic acid (Trans., 1897, 71, 1030), I was led to study the behaviour of the oxime towards an alkaline solution of potassium hypobromite. When treated with this agent, camphoroxime undergoes simultaneous bromination and oxidation, a quantitative yield of the compound, C10H16BrNO, being readily obtained if certain conditions are observed. The change is expressed by the equation C10H17NO+2KOBr=C10H16BrNO2 + KOH + KBr. The new derivative is not an oxime, being indifferent towards benzoic chloride, but it contains a nitroso-group, produced by removal of hydrogen from the oximido-residue. It is remarkably indifferent towards aqueous potash, from which it may be distilled without undergoing apparent change, whilst hot concentrated nitric acid scarcely dissolves it, and, at first, has no perceptible action on it. On dissolving the bromonitroso-derivative in concentrated sulphuric acid, the elements of water are withdrawn, and the compound C10H14BrNO, is produced. Unlike the substance from which it is obtained, this compound does not give Liebermann's reaction for nitrosoderivatives; moreover, cold concentrated nitric acid dissolves it immediately, whilst hot hydrochloric acid transforms it into an isomeride which yields a benzoyl derivative by the Schotten-Baumann method. These isomeric substances are optically inactive, although the initial compound is strongly lævorotatory. Under the influence of hot caustic alkalis, the isomerides, C1, H1,BrNO, break up in a remarkable manner, yielding a nitrile of the empirical 13 formula C,H1N. The production of such a compound involves elimination of carbon monoxide and hydrogen bromide in accordance with the equation, C10H14 BrNO = C2H1N+CO+HBr. 15 The nitrile, when hydrolysed with alcoholic potash, yields the corre sponding amide, which has the formula C,H,,NO, and is therefore isomeric with the amides of isolauronolic and camphoceenic acids; these, however, melt at 129-130° (G. Blanc, Compt. rend., 1896, 123, 749) and 155° (Jagelki, Ber., 1899, 32, 1506) respectively, whereas the new amide melts at 90°. Nevertheless, its relation to isolauronolamide must of necessity be a close one, because hydrochloric acid converts it into that substance along with isolauronolic acid. 14 It has been shown that when sodium orthoethylic camphorate is submitted to electrolysis, the ethylic salt of campholytic acid is formed (Walker, Trans., 1893, 63, 495); the acid itself is also obtained by the action of nitrous acid on dihydroaminocampholytic acid, produced on eliminating carbon monoxide from B-camphoramic acid, NH, CO C2H COOH, by the agency of sodium hypobromite (Noyes, Ber., 1895, 28, 547). Electrolysis of sodium orthoethylic camphorate also yields isolauronolic acid, first described by Walker, who then called it camphothetic acid (loc. cit.); the production of this compound from sulphocamphylic acid was recorded about a month later by Koenigs and Hoerlin (Ber., 1893, 28, 811), from whom it received its present name. These isomerides, isolauronolic and campholytic acids, are now regarded as the cis- and cistrans-modifications respectively of a single acid, mainly because both contain an unsaturated linking in the aß-position, and also on account of the readiness with which isolauronolic (cis-campholytic) acid is produced from the labile isomeride. Mere contact with cold dilute sulphuric acid at ordinary temperatures will suffice to convert the liquid campholytic acid into solid isolauronolic acid (Noyes, Ber., 1895, 28, 548), and in a private communication, Professor Walker informs me that an impure specimen of campholytic acid which has remained in his possession for some years, has now become almost entirely transformed into isolauronolic acid. (CH2),C CH-CH2 2 Neither the formula (CH3)2CC(CH):C-COOH' by which Blanc represents the structure of isolauronolic acid (Bull. Soc. Chim., 1898, [iii], 19, 534; compare also 1899, [iii], 21, 830), nor the expression CH, -C.COOH (CH),C CH(CH).CH , adopted by W. H. Perkin, jun. (Trans., 1898, 73, 796), suggests any reason for supposing that one of the two possible structural isomerides which have the unsaturated linking in the |
