Oxidative carbonylation of aniline to N,N′-diphenyl urea catalyzed by cobalt(II)–Schiff base complex/pyridine catalytic system

The oxidative carbonylation of aniline to N,N′-diphenyl urea was investigated by an efficient catalyst system comprising of Co(II)–Schiff base complex and a pyridine-type promoter. Effects of temperature, pressure, Schiff base ligands, catalyst loading and mole ratio of Co(II) complex to promoter on the catalytic activity were studied. When the reaction was carried out at 0.6 mol % of Co(II)salophen(OH)2, Co(II)salophen(OH)2/4-picoline (mol) = 2:1, CO/O2 (MPa) = 3:1, 150 °C, 7 h, the highest conversion of aniline and yield of N,N′- diphenyl urea were 85.3% and 79.2%, respectively. The mechanism based carbamoyl metal complex intermediate is also proposed.