Hydrogenation of p-nitrophenol to metol using Raney nickel catalyst: Reaction kinetics

Kinetics of the liquid-phase catalytic hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) and its conversion to metol have been investigated over a wide range of operating conditions. The effects of speed of agitation, hydrogen partial pressure, catalyst loading, substrate concentration and temperature on both the reactions have been reported. The effects of various solvents (2-propanol, methanol, dimethylformamide) on both the reactions have been investigated. Both the reactions were found to be first order with respect to the hydrogen partial pressure, first order with respect to PNP concentration for PAP formation and zero order with respect to substrate for metol formation. The experimental data could be fitted to the model involving a surface reaction controlling mechanism with dissociative adsorption of hydrogen for PNP hydrogenation and molecular adsorption of hydrogen for metol formation. The activation energies for the catalytic hydrogenation of PNP and metol formation were found to be 47 and 51 kJ mol−1, respectively.