Reaction Path of One-Pot Synthesis of Methyl N-Phenyl Carbamate from Aniline, Urea, and Methanol

One-pot synthesis of methyl N-phenyl carbamate (MPC) from aniline, urea, and methanol is a green reaction route. However, along which reaction path the reaction proceeds is still unclear and thereby the reaction mechanism cannot be determined. So the present work put much more emphasis on the analysis of the reaction path of MPC synthesis from aniline, urea, and methanol. First, the components in this reaction system were identified by means of gas-phase chromatograph (GC), high-performance liquid chromatograph (HPLC), and HPLC-mass spectrometry (MS) analyses. On the basis of the change tendency of the reaction components with reaction time, five plausible reaction paths were conjectured: one proceeds via a dimethyl carbonate intermediate, another utilizes methyl carbamate as an intermediate, still another passes a 1-phenyl biuret intermediate, yet another takes place through a phenylurea intermediate, and the last one carries on using diphenylurea as an intermediate. Then on the basis of thermodynamic analysis of the five possible reaction paths in combination with necessary experimental verifications, the one via a phenylurea intermediate was determined as the major reaction path in the absence of catalyst. Lastly, the influence of catalyst on the reaction path was studied and the result showed that the reaction path changed from through the phenylurea intermediate to the methyl carbamate intermediate in the presence of gamma-Al2O3 catalyst.