576 [May 21, 



V. " Notes of Researches on the Polyammonias, No. XXIII. 

 Hydrazobenzol, a new Compound isomeric with Benzidine." 

 By A. W. HOFMANN, LL.D., F.R.S., &c. Received May 7, 

 1863. 



The discovery, among the secondary products of the manufacture of 

 aniline, of xenylamine, the probable connexion of which with benzidine 

 (xenylene-diamine) I have already had an opportunity of pointing 

 out*, has induced me to submit the latter compound to some experi- 

 ments. In preparing benzidine by the process originally pointed out 

 by Zininf, viz. by treatment of azobenzol with sulphide of ammonium, 

 I was led to the observation of some phenomena which appear to 

 have escaped the attention of those who have hitherto studied this 

 substance. 



It is generally supposed that the action of reducing agents upon 

 azobenzol produces directly benzidine. 



C^N.+H^^H^. 



Azobenzol. Benzidine. 



Such, however, is not the case. The well-defined base designated 

 by the latter name is only a secondary product ; the first compound 

 which is generated in this process being a neutral or feebly basic body, 

 differing in all its properties from benzidine, with which, however, it 

 is isomeric, and into which it may be converted by simple treatment 

 with strong mineral acids. 



On passing a current of sulphuretted hydrogen into a solution of 

 azobenzol in alcoholic ammonia, the yellowish-red liquid is rapidly 

 decolorized, and yields on addition of water a crystalline precipitate 

 of a peculiar camphor-like smell. This substance contains a minute 

 quantity of the sulphur which separates, the bulk of which, however, 

 remains dissolved as polysulphide of ammonium ; it is easily purified 

 by two or three crystallizations from very dilute alcohol. Submitted 

 to combustion, the compound thus obtained yields numbers which 

 qoincide with those furnished by the analysis of benzidine. 



The properties in which the new substance, for which I propose 

 the name hydrazobenzol, differs from benzidine are the following : 

 Hydrazobenzol crystallizes from alcohol, and more especially from 



* Proc. Roy. Soc. vol. xii. p. 389. f Journ. Prakt. Chem. vol. xxvi. p. 93. 



