Fischer esterification requires which two substrates and catalyst?

• A. Alcohol and an aldehyde with base
• B. Carboxylic acid and an alcohol with an acid catalyst
• C. Ester and carboxylic acid with base
• D. Amide and alcohol with acid catalyst

Answer: (B)

Fischer esterification is an acid-catalyzed condensation between a carboxylic acid and an alcohol to form an ester and water. The acid catalyst protonates the carbonyl oxygen of the carboxylic acid, making the carbonyl carbon more electrophilic so the alcohol can attack. After alcohol addition and proton transfers, the tetrahedral intermediate collapses and water is expelled, regenerating the acid catalyst and yielding the ester.

This is why the substrates must be a carboxylic acid and an alcohol, not an aldehyde or an amide, and why an acid catalyst is required rather than a base. In practice, using an excess of alcohol and removing water helps drive the reaction toward ester formation.