The synthesis of phenyl isocyanate (PI) was studied by thermal decomposition of methyl N-phenyl carbamate (MPC) over tin catalysts. It has been found that di-n-butyltin oxide had higher activity. The unknown byproduct was determined as diphenylcarbodiimide (DPCD) by HPLC-MS. The results show that the formation of N,N'-diphenylurea (DPU) and DPCD are the main competitive reactions to the synthesis of PI. At normal pressure, the conversion of MPC is 85.17% and the yield of PI is 67.65% over Bu₂SnO under the optimal reaction condition, which is as follows: solvent, o-dichlorobenzene (ODCB); m(ODCB)/ m(MPC)＝15; n(Bu₂SnO)/n(MPC)＝0.075; reaction time, 1 h.

Key words: methyl N-phenyl carbamate, phenyl isocyanate, catalytic decomposition, di-n-butyltin oxide