Esters to Carboxylic Acids: Acid-Catalyzed Hydrolysis

Acid-catalyzed hydrolysis is another important reaction of esters.

In this reaction, an ester is hydrolyzed in the presence of aqueous acid to form carboxylic acid and alcohol.

This is a reversible reaction and precisely the reverse of a Fischer esterification reaction.

The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst, rendering the carbonyl carbon more electrophilic.

This is followed by a nucleophilic attack by water at the carbonyl carbon, forming a tetrahedral intermediate.

Next, deprotonation of the tetrahedral intermediate gives a neutral tetrahedral addition intermediate.

Subsequently, protonation of the alkoxy oxygen converts the alkoxy group into a better leaving group.

In the next step, the carbonyl group is re-formed with the departure of alcohol as a leaving group.

Finally, deprotonation yields a carboxylic acid and regenerates the acid catalyst.

Overall, an acid catalyst increases the electrophilicity of the carbonyl carbon and decreases the basicity of the leaving group.