Azoxy benzenes, hydrogenation

There are several recent methods for the reduction of azobenzene to hydrazobenzene in near-quantitative yield. Samarium(II) iodide reduces azobenzene to hydrazobenzene rapidly at room temperature. Hydrogen telluride, generated in situ from aluminum telluride and water, reduces both azobenzene and azoxybenzene to hydrazobenzene a mixture of phenyllithium and tellurium powder has been used to reduce azobenzene. A complex of the coenzyme dihydrolipoamide and iron(II) is also effective for the reduction of azo- and azoxy-benzene to hydrazobenzene the reduction probably involves coordination of the azobenzene to iron(II) as shown in structure (1). Electrochemical reduction has been used to prepare a number of hydrazobenzenes from the corresponding azobenzenes. In the presence of an acylating agent a diacylhydrazine (e.g. the pyridazinedione derivative 2) can be isolated from the electrochemical reduction of azobenzene. 

The hydrogenation of azoxy benzenes occurs in a stepwise fashion to give the azo and hydrazo compounds with final hydrogenolysis to the amine. The reaction can be stopped at any of these stages over W2 Raney nickel at room temperature and atmospheric pressure. With platinum oxide the hydrazine is obtained in very good yield. Hydrogenolysis to the amine occurs over all common metal catalysts but takes place most readily with palladium. 

Nitro compounds may be photoreduced by suitable hydrogen donors under sunlight. For example, nitrobenzene was reduced by toluene to yield aniline, 4-amino phenol, azoxy benzene, and benzoic acid. Alkyl aromatics that can form benzyl-type radicals were efficient hydrogen donors for this reaction. The sorption of nitrobenzene to humus with increased residence time and reaction sites will likely make this pathway play a significant role in the fate of nitrobenzene. Half-life of toluene calculated from smog chamber experi-... 

Nitro compounds in presence of carbonyl group are selectively reduced to amines in the presence of Raney nickel catalyst. Hydrazine reduces nitrdes yielding hydrazones. Under controlled reaction conditions other functional groups, including nitroso and oxime, may be reduced. Many partially hydrogenated derivatives, such as azo-, hydrazo-, and azoxy compounds may be obtained by partial reduction with hydrazine. Reaction with chlorobenzene yields benzene. 

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