Oxidative carbonylation of aniline over Pd/C catalyst: effect of promoters, solvents, and reaction conditions

Oxidative carbonylation of aniline to N,N'-diphenylurea over 5% Pd/C--- NaI catalyst has been reported. The effects of promoters, solvents, reaction conditions, and pretreatment of catalyst with reactants have been investigated. Pretreatment of 5% Pd/C catalyst with O2, CO, and aniline resulted initially in a decrease in the activity of the catalyst. Activity-versus-NaI concentration and activity-versus-O2 pressure curves passed through maxima, indicating inhibition of rates at higher concentrations. CO pressure showed a linear dependence below 35 atm pressure, but zero-order behavior at higher pressures. The variation in activity was 1.6th order with respect to aniline concentration. Higher activity is obtained in polar solvents. Process parameters had a strong influence on the activity of the catalyst, but the selectivity for N,N'-diphenylurea was unaffected