Synthesis of p-aminophenol by catalytic hydrogenation of nitrobenzene

The present work describes the preparation of p-aminophenol via single-step catalytic hydrogenation of nitrobenzene in acid medium. A conventional method of synthesis of p-aminophenol is a two-step reaction involving iron-acid reduction of p-nitrophenol, This method causes serious effluent disposal problems due to the stoichiometric use of iron-acid, which leads to the formation of Fe-FeO sludge (congruent to 1.2 kg/kg of product) in the process, which cannot be recycled, The single-step hydrogenation of nitrobenzene was carried out using platinum catalyst, and the process conditions were optimized. Complete conversion of nitrobenzene was achieved with selectivity to p-aminophenol as high as 75% under the best set of conditions. Furthermore, the catalyst can be easily recovered and efficiently recycled giving the TON as high as 1.38 x 10.(5) This paper presents studies on the effect of various process parameters such as temperature, hydrogen pressure, and substrate and acid concentration on the rate of reaction and selectivity to p-aminophenol.