Hydrazobenzene, from nitrobenzene

Electrolytic reduction, as in the preparation of hydrazobenzene from nitrobenzene, or of p-aminophenol from nitrobenzene. The latter reduction involves a simultaneous rearrangement of the intermediate phenylhydroxylamine. 

When reduced by electrolysis, nitrobenzene and its homologues yield the same products as may be obtained by the various chemical methods of reduction. Aniline, azobenzene, azoxybenzene, hydrazobenzene, and -amino-phenol, as well as phenylhydroxylamine, can thus be obtained from nitrobenzene, and most, if not all, of these products could be prepared satisfactorily on an industrial scale by electrolysis, by adjusting the manner of working so that economy of energy is combined with maximum yields. Many of these products demand a comparatively high price, so that low power cost is not so important in this class of manufacture as high percentage yields. 

Haussermann 2 reduced nitrobenzene and nitrotoluenes both in alkaline and acid solution, the former with iron, the latter with platinum, electrodes. By reduction in alkaline solution, he obtained as principal product hydrazobenzene and hydrazo-toluene respectively in sulphuric-acid solution he got from nitrobenzene, as chief products, benzidine sulphate and azoxy-benzene, besides an easily changeable body which was not further determined. o-Nitrotoluene3 under like conditions gave o-tolui-dine sulphate besides small quantities of o-toluidine p-nitro-toluene yielded principally p-toluidine. 

Benzidine rearrangement of hydrazobenzene is used to obtain 4,4 -diphenyldi-amines from nitrobenzenes. This reaction occurs intra-molecularly, by way of a p-quinonoid intermediate. 

Diaminodiphenyl derivatives can be obtained from appropriately substituted nitrobenzenes by a rather dated process of alkaline reduction with zinc powder/ sodium hydroxide solution, which affords hydrazobenzene. A more recent method uses a catalytic reduction process with hydrogen and specifically deactivated catalysts of precious metals. Subsequent acid-catalyzed rearrangement with hydrochloric acid yields the hydrochloride of the target diamine ... 

To a mixture of 50 g (0.4 mol) of nitrobenzene, 180 ml of 30% sodium hydroxide, 20 ml of water and 50 ml of ethanol, 100-125g (1.5-1.9g-atom) of zinc dust is added portionwise with efficient mechanical stirring until the red liquid turns light yellow. After stirring for an additional 15 minutes, 1 liter of cold water is added, the mixture is filtered with suction, the solids on the filter are washed with water, and the hydrazobenzene is extracted from the solids by boiling with 750 ml of ethanol. The mixture is filtered while hot, the filtrate is cooled, the precipitated crystalline hydrazobenzene is filtered with suction, and the mother liquor is used for repeated extraction of the zinc residue. Recrystallization of the crude product from an alcohol-ether mixture gives hydrazobenzene of m.p. 126-127°. 

Pentonitroozobenzene, (N02)3 -CjHj N QHj NOjJj orn colored ndls (from glacial acetic acid mp 213°, explodes on heating above its mp readily sol in acet, ethyl acetate or nitrobenzene diffc sol in ale, eth or benz. It was prepd by heating an acetonic soln of 2,4,6,2,4 -pentanitro-hydrazobenzene, [(N02)2-C8H3-NH-NH-QH2-(N02)3], with an excess of lead peroxide for Vi hr... 

Azobenzene has been manufactured by reduction of a suspension of nitrobenzene by Na(Hg). Further reduction to hydrazobenzene is possible if higher temperatures and concentrations of alkali are employed [79]. The corresponding arsenic compounds may be prepared from a phenylarsenoxide by amalgam reduction thus -aminophenylarsen-oxide yields 80% H9NC6H4As=AsC6H4NHt on treatment with 4% Na(Hg) in methanol [80]. 

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