Phosgene-free synthesis of phenyl isocyanate by catalytic decomposition of methyl N-phenyl carbamate over Bi2O3 catalyst

A phosgene-free approach for the synthesis of phenyl isocyanate (PI) was developed, using the heterogeneous catalytic decomposition of methyl N-phenyl carbamate (MPC). Twenty oxide-catalysts were investigated and compared; the Bi(2)O(3) catalyst gave the better catalytic performance. From bismuth (III) nitrate pentahydrate, Bi(2)O(3) was prepared by different methods, which included the direct decomposition, mechano-chemical method, direct precipitation and indirect precipitation. The catalysts were characterized by N(2) adsorption/desorption, XRD, FTIR and TEM analyses. After optimization, the Bi(2)O(3) catalyst prepared by direct calcination of bismuth (III) nitrate pentahydrate at 723 K in air for 4 h gives the best activity. When the reaction was carried out at the boiling temperature of o-dichlorobenzene (ODCB) at normal pressure, the optimal reaction conditions over Bi(2)O(3) catalyst are as follows: the mass ratio of catalyst/MPC is 0.05, mass ratio of ODCB/MPC is 15:1, reaction time of 60 min. The optimized conversion of MPC and the yield of PI are 86.2% and 78.5%, respectively. There was a good durability for the Bi(2)O(3) catalyst, and the species of Bi (III) ions of catalyst were partially oxidized to Bi (IV) ions during the reaction, supported by the results of XRD and XPS techniques.