Question

Diazomethane can be used to convert a carboxylic acid to a methyl ester. Propose a mechanism for this reaction.

Short answer

Diazomethane constitutes a molecule comprising methylene carbon and dinitrogen connected to it. It is made by the decomposition of several derivatives of N-methyl-N-nitrosamines. The treatment of carboxylic acid with diazomethane produces methyl esters.

Step-by-step solution

Diazomethane

Diazomethane constitutes a molecule comprising methylene carbon and dinitrogen connected to it. It is made by the decomposition of several derivatives of N-methyl-N-nitrosamines. The treatment of carboxylic acid with diazomethane produces methyl esters.

The mechanism for the conversion of carboxylic acid to an ester using diazomethane

The first step involves the protonation of diazomethane by the carboxylic acid that forms a carboxylate ion.

This ion attacks the methyl group of CH₃-N₂, in which CH₃-N₂ is a good alkylating agent and N₂is a good leaving group. This leads to the formation of methyl ester and N₂. The mechanism is given below.