Reactions

The Steglich esterification begins with the activation of the carboxylic acid by the DCC. The carboxylic acid is deprotonated by one of the imine nitrogens of DCC. Then, the new carboxylate performs a nucleophilic attack on the electrophilic central carbon of DCC, forming an O-acylisourea intermediate. DMAP derivative then acts as a nucleophile and attacks the electrophilic carbonyl carbon of the intermediate. This displaces dicyclohexylurea (DCU) as a by-product and generates a reactive N-acylpyridinium species. This step is critical, as the N-acylpyridinium is a far better acylating agent than the O-acylisourea intermediate. The alcohol then attacks the electrophilic carbonyl carbon of the N-acylpyridinium in a nucleophilic acyl substitution, releasing DMAP. Collapse of the intermediate, with proton releasing, yields the desired ester product.