Electrolytic Reduction of Nitrobenzene to Hydrazobenzene

Abstract

In small scale experiments on the electrolytic preparation of hydrazo‐benzene from nitrobenzene in alkaline emulsion it was found that cathodes of zinc, tin, cadmium, and lead with more than 0.07 mole of spongy layer per square decimeter of the surface were most suitable for the reduction. As base materials for the spongy layers, common metals such as Pb, Fe, and others were found to be useful. At these cathodes, almost quantitative yields of hydrazobenzene were obtained at relatively high current densities with suitable agitation. The mechanism is believed to consist of true electrochemical reduction of nitrobenzene to azoxy‐ or azobenzene, followed by further chemical reduction of the azobenzene by sponge metal. The mechanism gains support from results of polarographic measurements which show that, while nitrobenzene is an active depolarizer with or without organic solvent in the catholyte, azobenzene is active only when a solvent such as alcohol is present.In the interest of developing a practical electrochemical preparation of hydrazobenzene, preliminary runs have been made in a larger cell using 1.5 kg of nitrobenzene; material yields of hydrazobenzene up to 90% and current efficiencies of 80% at 17 amp/dm2 have been obtained, compared with yields of 95% and efficiencies as high as 88% at 30 amp/dm2 obtained with the small cell.