The formation of an ester from a carboxylic acid and an alcohol in the presence of sulfuric acid as a catalyst is known as Fischer esterification. The reaction proceeds through an acid-catalyzed nucleophilic acyl substitution mechanism. Here is the stepwise mechanism:1. Protonation of the carbonyl oxygen:The sulfuric acid H2SO4 acts as a catalyst and protonates the carbonyl oxygen of the carboxylic acid, making it a better electrophile. This step generates a resonance-stabilized oxonium ion.2. Nucleophilic attack by the alcohol:The alcohol acts as a nucleophile and attacks the carbonyl carbon of the protonated carboxylic acid. This leads to the formation of a tetrahedral intermediate.3. Proton transfer:A proton from the newly formed hydroxyl group OH in the tetrahedral intermediate is transferred to a nearby alcohol molecule or to the conjugate base of the sulfuric acid HSO4- , which acts as a base.4. Elimination of water:The tetrahedral intermediate collapses, and the electrons from the oxygen-hydrogen bond move to form a double bond between the carbonyl carbon and oxygen, resulting in the elimination of a water molecule.5. Deprotonation of the ester:The ester product is protonated, so it undergoes deprotonation by a nearby alcohol molecule or the conjugate base of the sulfuric acid HSO4- , which acts as a base. This step regenerates the sulfuric acid catalyst and forms the final ester product.In summary, the sulfuric acid acts as a catalyst by protonating the carbonyl oxygen, making it more electrophilic and facilitating the nucleophilic attack by the alcohol. The alcohol acts as a nucleophile, attacking the carbonyl carbon and leading to the formation of the ester. The reaction proceeds through a series of proton transfers and the elimination of water, with the sulfuric acid being regenerated in the final step.