Phosgene-Free Synthesis of Phenyl Isocyanate by Catalytic Decomposition of Methyl N-Phenyl Carbamate over Bi2O3 Catalyst

Abstract

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 Bi₂O₃ catalyst gave the better catalytic performance. From bismuth (III) nitrate pentahydrate, Bi₂O₃ was prepared by different methods, which included the direct decomposition, mechano-chemical method, direct precipitation and indirect precipitation. The catalysts were characterized by N₂ adsorption/desorption, XRD, FTIR and TEM analyses. After optimization, the Bi₂O₃ 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 Bi₂O₃ 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 Bi₂O₃ 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.