Question

Propose a mechanism for the reaction of phenyl isocyanate with methanol.

Short answer

Complete mechanism for the reaction

Step-by-step solution

Urethanes (or carbamate ester)

They are commonly made by treating an isocyanate with an alcohol or a phenol. The reaction is highly exothermic and it gives a quantitative yield of carbamate ester.

Mechanism for the reaction of phenyl isocyanate with methanol

In this reaction, nucleophilic addition of methanol takes place in a concerted way across the nitrogen double bond carbon (N=C) of the phenyl isocyanate. Another methanol molecule adds to the reaction as a result of which a protonated methyl alcohol is formed. The double bond around N=C gets rearranged to give the final product as methyl-N-phenylcarbanate .

Complete mechanism for the reaction