One-pot synthesis of methyl n-phenyl carbamate from aniline, carbon dioxide and methanol

摘要

BACKGROUND: Methyl N-phenyl carbamate (MPC) is an intermediate for the manufacture of methylene diphenyl diisocyanate (MDI) by a non-phosgene route. The synthesis of MPC from aniline, carbon dioxide and methanol can transform the greenhouse gas carbon dioxide into value-added product, MPC. RESULTS: Bicyclic amidine (DBU)-acetonitrile was found to be an excellent catalyst-solvent combination for MPC synthesis. Under the reaction conditions of initial pressure of carbon dioxide 1 MPa, reaction time 5 h, reaction temperature 180℃, volumetric ratio of methanol/aniline 1:4, volumetric ratio of acetonitrile/aniline 1:1, and mass percentage of DBU 5.6%, the conversion of aniline was 7.1% and the selectivity of MPC was 25.3%. A plausible catalytic reaction mechanism was proposed. The results of alkyl N-phenyl carbamate (APC) synthesis from aniline, carbon dioxide and alcohol (methanol, ethanol, propanol or butanol) showed that the conversion of aniline and the selectivity of the corresponding APC decreased significantly with increase of the stereo hindrance on the alcohol substrate. CONCLUSION: The reaction of aniline, carbon dioxide and alcohol to APC, especially MPC, can be achieved even though stereo hindrance on the alcohol substrate limits the reaction.