p-aminophenol synthesis in an organic/aqueous system using Pt supported on mesoporous carbons

The biphasic conversion of nitrobenzene to p-aminophenol (PAP) via Pt/C-catalyzed hydrogenation of nitrobenzene and an acid-catalyzed rearrangement of the N-phenylhydroxylamine intermediate was studied. The effects of Pt/C catalyst loading, type of carbon support, reaction temperature, acid catalyst concentration, and additives on the reaction rate and PAP selectivity were investigated. At a given catalyst loading, nitrobenzene conversion and PAP selectivity were favored under a high reaction temperature and a high aqueous acid concentration. An increase in PUC catalyst loading leads to an increased hydrogenation rate but a lower PAP selectivity. Nitrobenzene conversion and PAP selectivity are both promoted by a small addition of NN-dimethyl-n-dodecylamine, which may act as a phase transfer agent or emulsifier. Pt catalysts supported on novel mesoporous carbons - CMK-1 and CMK-3, which have uniform pore diameters of 3 and 4.5 nm - significantly outperform their counterpart supported on activated carbon with micropores. Two percent Pt/CMK-1 shows a catalytic activity equivalent to that of 5% Pt/C, but with significantly better PAP selectivity, i.e., 84% compared to 72%. (c) 2007 Elsevier B.V. All rights reserved.