Alcoholysis is a nucleophilic acyl substitution reaction in which an alcohol functions as a nucleophile. Acid halides react with alcohol to produce esters. The mechanism proceeds in three steps:

1. First, the alcohol acts as a nucleophile and attacks the acyl carbon to form a tetrahedral intermediate.
2. Next, the carbonyl re-forms with the loss of a chloride ion.
3. Lastly, the positively charged intermediate loses a proton to give an ester as the final product along with H₃O⁺, making HCl an overall byproduct of the reaction.

Pyridine is used as a base to neutralize the acidic reaction mixture.

Alcoholysis of sulfonyl chlorides follows a similar pattern and forms sulfonic acid esters.