View Article Online / Journal Homepage / Table of Contents for this issue ACTION OF PIIOSPHORUS PENTACHLORIDE ON BENZAMlDE. 1143 Benxamide. By ARTHURWALSH TITHERLEY and ELIZABETHWORRALL. DURINGan investigation, which is still in progress, of the behaviour of secondary amides with phosphorus pentachloride, the action of the latter on simple primary amides came incidentally under considera- tion. Practically the whole of our available knowledge of the behaviour of primary amides with phosphorus pentachloride arises from Wallach’s extensive investigation (AnnuZen,1877, 184, l),which apparently left little further to be done in this direction. The net result of his work, based chiefly on the case of ethyl oxamate (oxa- methane) led him to the conclusion (i) that the carbonylic oxygen in the amido-group was first replaced by two chlorine atoms ; (ii) that the resulting “ dichloramide ” (I) which was very unstable, readily lost hydrogen chloride (1 molecule), yielding the unstable ‘‘ imide chloride ” (TI), and (iii) that the latter finally lost another molecule of hydrogen chloride, yielding the nitrile, thus :- *CO*NH,cc$ *CCl,*KH, -”: *CCl:NH -I?!!*CN, (1.) (11.) In the case of oxamethnne, unstable derivatives of types (I) and (11) were isolated in an impure condition, but apparently, in the case of all the other amides investigated, phosphorus derivatives containing oxygen and chlorine were produced. A derivative containing phos- phorus was also obtained by Wallach in the case of oxamethane, Published on 01 January 1909. Downloaded by Dalhousie University 19/05/2015 08:44:17. having the formula C,H,O,Ci,NP. In the case of benzamide, with phosphorus pentachloride in the cold, Wallach obtained a liquid which he considered to be a mixture of benzonitrile and phosphoryl chloride, but by gentle warming he obtained a liquid which, on coolingstrongly, set to a crystalline mass containing phosphorus. This solid compound decomposed at once in air, and was not further investigated. A critical survey of Wallach’s results would suggest that the general action of phosphorus pentachloride on simple primary amides leads to the production of phosphorus compounds and not the simple derivatives of types I and 11, and that such phosphorus compounds readily decompose on heating yielding phosphoryl chloride and the corresponding nitrile. The inconclusiveness of Wallach’s results with respect to benzamide led the authors to examine its behaviour wilh phosphorus pentachloride more closely. The conclusions which have been arrived at are mentioned below, but after these had been reached and the work had been nearly completed, a, recent paper by Steinkopf View Article Online 1144 TITHERLEY AND WORRALLi THE ACTION OF (Ber., 1908, 41, 3571) came under the authors' notice, in which the action of phosphorus pentachloride on halogenated acetamides is described, and, to a large extent, similar conclusions have been drawn. Originally it was intended by the authors to describe their work on benzamide and dibenzamide in one paper, but as the portion referring to the latter is incomplete, it was considered advisable, since Steinkopf is at work in a similar field, to publish at once the results so far as they relate to benzamide. When benzamide and phosphorus pentachloride react at 15O, slightly more than one molecular equivalent of hydrogen chloride is evolved, and since in no circumstances does interaction occur without formation of hydrogen chloride it is clear that the ' dichloride,' C,H,*CCl,*NH, (aa-dichloro benzy lamine), cannot be formed except :as an intermediate stage. The production of this derivative, however, as a first stage in the reaction can hardly be doubted in view of the general facts established by Wallach. In the subsequent change in- volving elimination of one molecule of hydrogen chloride, two things may be expected, namely, (i) the aa-dichlorobenzylamine may lose hydrogen chloride, yielding a-chlorobenzimide, or (ii) it may react with the phosphoryl chloride present, yielding a phosphorus derivative : I. C,H,*CCl,.NH, --+ C,H5*CC1:NH -I- HCl. (a-Chlorobenzimide, 1 11. C,H~°CUI~*N_EI,+ POCl, --+- C,H5*CCI,oN13*POC1,4- HCl. (aa-l>iclilo~obenzylphos~~li~iiliC:cliloride.) In any case the liquid obtained in ths action between benzamide and phosphorus pentachloride at 15' cannot be a mixture of benzo- nitrile and phosphoryl chloride as Wallach supposed, since such a mixture would require the loss of two molecular equivalents of Published on 01 January 1909. Downloaded by Dalhousie University 19/05/2015 08:44:17. hydrogen chloride. This liquid, on treatment with water, yields bensonitrile, whilst on keeping in the cold for several hours in absence of moisture it slowly loses a molecule of hydrogen chloride, leaving a mixturs which consists essentially of benzonitrile and phosphoryl chloride, and the same result is attained very rapidly by heating the liquid produced at 15' to 50'. A totally different result, however, is obtained if the action between benzamide and phosphorus pentachloride is carried out at 50', or even at 15O, when such solvents as benzene or chloroform are present. The resulting liquid obtained under these conditions on careful treatment with water yields a mass of colourless crystals containing chlorine and phosphorus, which on investigation proved to be a benzoyl derivative of phosphamic chloride, namely, C,H,*CO*N€€*POCl,. This remarkable difference in results, produced by such slight difference in conditions, led the authors to examine closely the pro- View Article Online PHOSPHORUS PENTACHLORIDE ON BENZAMIDE. 1145 ducts obtained under a large variety of conditions, and the conclusions arrived at may be stated thus : I. In the cold without solvent the ‘di~hloramide,~first formed, immediately loses hydrogen chloride, yielding chiefly a mixture of a-chlorobenzimide, C,H,*CCl: NH, and phosphoryl chloride, together with other products in small quantities (see p. 1148). The former is very unstable, and decomposes slowly at 15*, and immediately at SO”, or, on treatment with water, into benzonitrile and hydrogen chloride. On account of its instability it is impossible to isolate this a-chloro- benzimide, which, moreover, could not be separated by strong cooling or treatment with light petroleum, 11. In the cold, in presence :of benzene or chloroform, the ‘di- chloramide ’ first formed immediately reacts with the phosphoryl chloride simultaneously produced, yielding aa-dichlorobenzylphos- phamic chloride, C,H,*CCl,*NH*POCl,, which, on heating to 50°, loses hydrogen chloride, yielding a-chlorobenzylidenephosphamic chloride : C6H5*CC12*NH*POCI,-+ C6H5*CCI:X*POCl, + HCI. This product, moreover, results directly when benzamide and phos- phorus pentachloride, without a solvent, are heated to SO’, two molecules of hydrogen chloride being evolved, but a considerable amount of benzonitrile and phosphoryl chloride is also formed. The influence of a solvent in inducing the formation of phosphorus deriv- atives is very striking, and by adding benzene at different stages of the action and examining the resulting product, after exposure to moist air, for benzoylphosphamic chloride, it was possible to shaw that the influence of the solvent in the reaction between benzarnide and phosphorus pentachloride is not operative after the first molecule of hydrogen chloride has been evolved, but exerts itself in the reaction Published on 01 January 1909. Downloaded by Dalhousie University 19/05/2015 08:44:17. involving elimination of hydrogen chloride. The effect of a solvent, which is similar to that of heat, must be to induce the hypothetical aa-dichlorobenzylamine to react with the phosphoryl chloride with liberation of hydrogen chloride, whilst in absence of solvent at lower temperatures the act-dichlorobenzylamine spontaneously decomposes without acting on the phosphoryl chloride, yielding a-chlorobenzimide, C,H,*CCl:NH. There is, however, no direct proof available of the actual production of the latter compound ; treatment of the supposed mixture of this substance and phosphoryl chloride with a benzene solution of aniline at low temperatures failed to yield phenylbenz- amidine, but having regard to the great instability which might be expected to characterise a-chlorobenzimide, it is likely that the aniline simply effected removal * of hydrogen chloride yielding benzonitrile * A siuilar removal of hydrogen chloride: by aniline Iias been shown to take place with certain phosphorus derivatives (see p. 1146). View Article Online 1146 TITHERLEY AND WORRALL: THE ACTION OF which was found, Moreover, attempts to prepare a-chlorobenzimide by the action of hydrogen chloride on benzonitrile at low temperatures were unsuccessful. In regard to the two possible reactions, I. C,H,*CCl,*NH, -+ C,H,*CCl:NH + HCl. 11. C,H5*CC1,*NH, +POCl, -+ C,~,~CCl,*NH*POCJ~+HCI, it would appear that whilst the velocity of (I) is not influenced by benzene and chloroform the velocity of (11) is greatly accelerated by these solvents and by rise of temperature. As already noted, Wallach (Zoc. cit.) isolated a cornpound similar to that formed in (11), by the action of phosphorus pentachloride on oxamethane. The product of the action in the cold was a clear liquid, evidently consisting of a mixture of phosphory ;chloride and the unstable compound, CO,Et.CCI,*N H2, which was precipitaied in needles by light petroleum. The mother liquor, however, on keeping, deposited crystals the composition of which corresponded with the formula C0,Et*CCl,*NH9POC12. The most interesting feature, however, in councvion with this substance is the fact that it was only formed under the c'ztalytic influence of R trace of moisture. As in tho authors' expeiiments moisture was carefully excluded by means of phosphoric oxide, it is probable that benzene and chloroform behaved catalytically in a similar manner, that is, accelera- ting reaction (11) above, and indeed it was shown in one ex1)eriment that a relatively small quantity of chloroform gave LL nearly quanti- tative yield of the phosphorus derivative. The behaviour of a-clilorobenzylideLIephosph~~iicchloride with moisture is very remarkable, seeing that the two chlorine atoms Published on 01 January 1909.