585 



VI. " Contributions towards the History of Azobenzol and Ben- 

 zidine." By P. W. HOFMANN, Ph.D. Communicated by 

 Dr. HOFMANN. Received July 24, 1860. 



Among the numerous compounds into which benzol, when sub- 

 mitted to reagents, is converted, azobenzol and its derivatives have as 

 yet received but limited attention. Although more than twenty- 

 five years have elapsed since this interesting body was discovered 

 by Mitscherlich, both its formation and its constitution remain still 

 doubtful. 



Mitscherlich*, who discovered azobenzol in 1834, when submitting 

 nitrobenzol to the action of an alcoholic solution of potassa, repre- 

 sented this compound by the formula 



C 6 H 5 Nf, 



but left the reaction which gives rise to the formation of azobenzol 

 unexplained. In 1845 this body was reprepared by Hofmann and 

 Muspratt^, who observed among the collateral products of the reac- 

 tion aniline and oxalic acid. They represent the formation of 

 azobenzol by the equation 



2C 6 H 5 N0 2 +C 2 H 6 0=C 6 H 5 N + C 6 H 7 N-fC 2 H 2 4 +H a O, 



Nitrobenzol. Alcohol. Azobenzol. Phenylamine. Oxalic acid, 

 adding at the same time that they are far from considering this 

 equation as more than the representation of one phase of the trans- 

 formation of nitrobenzol, since several other rather indefinite com- 

 pounds or products are formed simultaneously. 



At about the same period Zinin made the interesting observation 

 that azobenzol is capable of fixing hydrogen and of being thereby 

 converted into a well-defined base, benzidine, which he represented 



by the formula 



C 9 H,N. 



Considering the physical characters both of azobenzol and of ben- 

 zidine, especially the high boiling-points of these substances, and the 

 ratio of hydrogen and nitrogen in the latter compound, the sum of 



* Pogg. Ann. xxxii. p. 224. 

 f H = l,0 = 16, C = 12, &c. 

 J Mem. of the Chem. Soc. vol. iii. p. 113. 



