ELECTROLYTIC REDUCTION 591 



in alcoholic alkaline solution, the chief products are the azo- and 

 azoxy-compounds, while in acid solution the reduction is carried 

 further, and the hydrazo- and amino-compounds are chiefly 

 formed. This difference in the phase to which nitrobenzene is 

 reduced in alkaline and acid solution, Lob ascribes, in the case 

 of an alkaline solution, to the liberated sodium causing the 

 reduction rather than the nascent hydrogen. 1 



Haussermann 2 was the first to obtain benzidine — 



NH 3 - C 6 H 4 - C 6 H 4 - NH 2 



as an electro-reduction product of nitrobenzene, Lob 3 subse- 

 quently obtaining benzidine in excellent yield by reducing 

 first to the azo-phase in alkaline solution, and completing the 

 reduction in dilute sulphuric acid solution. Lob also reduced 

 many derivatives of nitrobenzene, such as the nitrobenzoic 

 acids. 



The first attempt to follow these electro-reduction processes 

 quantitatively was made by Elbs, 4 who showed that the 

 reducibility of nitro-compounds diminished as the number of 

 nitro groups is increased. The quantitative investigation of 

 these processes was, however, much more fully worked out 

 by Tafel for difficultly reducible substances, and is described 

 later. 



Lob 5 called attention to the effect of different kinds of 

 cathodes on the reduction of nitrobenzene, a factor which is of 

 primary importance with difficultly reducible substances. Thus 

 tin and copper electrodes yielded more aniline, nickel more 

 azoxybenzene. Elbs 6 also showed that under otherwise equal 

 conditions, nitrobenzene was more quickly reduced at a lead 

 cathode yielding more aniline, than at a platinum cathode, at 

 which more amidophenol was produced. 



The following scheme shows at a glance the different reduc- 

 tion products which nitrobenzene has yielded, the reduction of 

 this substance, and of its derivatives, by means of the electric 



1 Lob, Zeitschr. f. Electroc. 2 (1896), 529. 



2 Chem.-Ztg. 17 (129). 



3 Zeitschr. f. phys. Chem. 34 (1900), 641 ; Zeitschr. f. Electroc. 7 (1900), 320. 



4 Journ. f. prak. Chem. 43 (1891), 39. 



5 Zeitschr. f. Electroc. 4, 430 ; Lob and Moore, Zeit. f. phys. Chem. 47 

 (1904), 418. 



6 Zeitschr. f. Electroc. 2, 472. 



