In Fischer esterification, what is the role of concentrated sulfuric acid?

• A. It is the solvent.
• B. It is the product.
• C. It acts as a catalyst to speed up the esterification.
• D. It is the reactant.

Answer: (C)

Concentrated sulfuric acid acts as a catalyst in Fischer esterification. It donates protons to the reacting species, making the reaction proceed faster without being consumed. Specifically, it protonates the carbonyl oxygen of the carboxylic acid, increasing the electrophilicity of the carbonyl carbon so the alcohol can attack more readily. It also helps convert the leaving group into water, facilitating the formation of the ester through the tetrahedral intermediate. In addition, the strong acid also acts as a dehydrating agent, removing water from the mixture and shifting the equilibrium toward the ester product. It is used in catalytic amounts, not as the solvent, product, or reactant.