Synthesis of p-Aminophenol by Catalytic Hydrogenation of p-Nitrophenol

The catalytic hydrogenation of p-nitrophenol to p-aminophenol was investigated in a laboratory-scale batch-slurry reactor. Pt/C catalyst (1%) was chosen for optimization of reaction conditions and kinetic studies because of its higher catalytic activity compared to that of other heterogeneous transition metal catalysts. The average catalytic activity and initial rate of hydrogenation was found to increase with increase in the solvent polarity. To investigate the intrinsic kinetics of the reaction, the effect of catalyst loading, agitation speed, p-nitrophenol concentration, and hydrogen partial pressure on the initial rate of hydrogenation was studied at different temperatures. The analysis of initial rate data indicated that the mass-transfer resistances were not significant under the prevailing reaction conditions. A simple Langmuir−Hinschelwood (L−H)-type model was found to represent the kinetics of hydrogenation of p-nitrophenol to p-aminophenol satisfactorily. The apparent energy of activation was found to be 61 kJ/mol.