THE REDUCTION OF NITROBENZENE BY HYDROSULPHIDE ION IN AQUEOUS MEDIA

Abstract

The reduction of nitrobenzene by sodium hydrosulphide and sodium hydrodisulphide in aqueous media at 50° has been examined. Goldschmidt's report of first-order dependence upon both nitrobenzene and hydrosulphide is corroborated. The action of hydrosulphide on nitrobenzene produces phenylhydroxylamine, which is reduced by hydrosulphide much more slowly than is nitrobenzene. As reaction progresses, nitrobenzene reduction produces yellow hydrodisulphide, which is responsible for the observed autocatalytic effect. Hydrodisulphide reduces phenylhydroxylamine more rapidly than it does the original nitrobenzene, and hence as reaction time is extended, phenylhydroxylamine disappears more rapidly than does nitrobenzene, yielding only aniline and some unreacted nitrobenzene towards the end of the reaction. Hydrosulphide reduction of phenylhydroxylamine to aniline produces thiosulphate but apparently no hydrodisulphide. Hydrodisulphide reduction of the phenylhydroxylamine leads only to conversion of the yellow hydrodisulphide to a colorless species, apparently thiosulphate. On the other hand hydrosulphide or hydrodisulphide reduction of nitrobenzene is accompanied by thiosulphate formation and some increase in hydrodisulphide. A comparison of the rate constants shows that under the conditions of the reaction, hydrodisulphide ion reduces nitrobenzene about seven times more rapidly than does hydrosulphide ion while phenylhydroxylamine is reduced two to three times more rapidly by hydrodisulphide than is nitrobenzene.