Clean synthesis of methyl N-phenyl carbamate over ZnO-TiO2 catalyst

BACKGROUND: Methyl N-phenyl carbamate (MPC) is an intermediate for the preparation of methylene diphenyl diisocyanate (MIDI), which is an important monomer for polyurethane synthesis. The synthesis of MPC by the reaction of aniline and dimethyl carbonate (DMC) is becoming more and more attractive. However, most of the catalysts used in MPC synthesis are homogeneous and not environment-friendly. Therefore, it is important and necessary to develop a new kind of oxide catalyst, that is not only friendly to the environment, but also exhibits higher activity and longer service time. RESULTS: A new heterogeneous catalyst, ZnO-TiO2, was prepared for MPC synthesis. ZnO-TiO2 catalyst with a molar ratio Ti/Zn = 2 and calcined at 673 K exhibited good catalytic activity: aniline conversion was 96.9% and MPC yield 66.7%. CONCLUSION: ZnO-TiO2 exhibits better catalytic activity than ZnO or TiO2 alone, which may result from the formation of ZnTiO3 and Zn2TiO4. Compared with ZnTiO3, Zn2TiO4 has better selectivity for MPC synthesis. Lewis acid sites with weaker acid strength favour MPC synthesis. The catalyst activity can be recovered almost completely by calcination. (C) 2008 Society of Chemical Industry