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.