What is the name of the reaction between a carboxylic acid and an alcohol to form an ester?

• A. Aldol condensation
• B. Saponification
• C. Fischer esterification
• D. Hydrogenation

Answer: (C)

Esters form by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst in a process known as Fischer esterification. The acid protonates the carbonyl oxygen, making the carbonyl carbon more electrophilic. The alcohol then attacks this carbon, creating a tetrahedral intermediate. Through proton transfers, the -OH group of the carboxyl eventually leaves as water, and the alcohol fragment becomes the alkoxy part of the ester. Removing water as the reaction proceeds helps push the equilibrium toward the ester product. The result is an ester with the general formula RCOOR'. This differs from aldol condensation, which forms β-hydroxy carbonyl compounds, from saponification, which is the base-catalyzed hydrolysis of esters to carboxylate salts and alcohol, and from hydrogenation, which adds hydrogen to unsaturated bonds.