A New Nonphosgene Route to Synthesize Methyl n-Phenyl Carbamate from Phenyl Urea and Methanol

摘要

Isocyanates are commercially synthesized by the reaction of phosgene with amines. The reaction has serious drawbacks such as toxicity and corrosion. Therefore, the synthesis of isocyanates via a non-phosgene route has attracted considerable attention. Several methods for preparing methyl N-phenyl carbamate (MPC), which can be transformed into isocyanates by thermal cracking, have been reported. For example, MPC could be formed by the oxidative carbonylation of aniline with CO, the reductive carbonylation of nitrobenzene with CO and methanol, and the methoxycarbonylation of aniline with dimethyl carbonate. Differing from the methods mentioned above, a novel non-phosgene way for the MPC synthesis through the reaction of phenyl urea and methanol was proposed. In this reaction, methanol is used both as reactant and solvent. The theoretic products are MPC and ammonia. This means that the separation of products could be realized easily. In our work, the synthesis of MPC was performed in a 100mL autoclave with stirring. The conversion of phenyl urea and the selectivity of products were determined by a Shimadzu GC-14B gas chromatograph equipped with PEG-20M capillary column, using diphenyl as an internal standard sample for quantitative analysis. The effects of catalysts, temperature and mole ratio of methanol/phenyl urea on the reaction were investigated. The catalytic mechanism was discussed too.