Hydrogenation of substituted nitroarenes by a polymer-bound palladium(II) Schiff base catalyst

The catalytic activity of a polymer-bound palladium Schiff base catalyst was investigated toward the reduction of aryl nitro compounds under ambient temperature and pressure. The dependence of the rate of hydrogenation of o-nitroaniline and o-nitrotoluene on substrate concentration, catalyst concentration and temperature has been determined. Based on the results obtained a plausible mechanism for the hydrogenation reaction is proposed and a rate expression is deduced. The energy and entropy of activation have been evaluated from the kinetic data. The polymer-bound catalyst was found to be better than its homogeneous analog PdCl2(NSBA) [NSBA = N-salicylidene benzylamine] for both stability and reusability. Recycling studies revealed that the catalyst could be used six times without metal leaching or significant loss in activity.