Hydrogenation of Nitrosobenzene over Palladium Catalysts

Abstract

During the hydrogenation of aromatic nitro compounds over transition metal catalysts aromatic nitroso compounds are active intermediates resulting from an early step. By proper selection of reaction conditions the nitroso intermediates can either form amines from further hydrogenation of the hydroxylamines or form bimolecular products from coupling reactions with the hydroxylamines. These latter are favored in alkaline media. Nitrosobenzene was purchased from Fluka and Sigma. The unpurified form was about 99% pure, so purification was accomplished by recrystallization from methanol thrice. Phenylhydroxylamine was prepared in pure form using known procedures. Both purified and unpurified nitrosobenzene were hydrogenated over the four Pd/SiO2 catalysts under the standard conditions. Two reaction products, aniline and hydrazobenzene, were obtained when hydrogen consumptions ceased and some interesting results were observed.