7. What is the role of H3PO4 in aspirin synthesis?

Answer:Aspirin is synthesized by esterification reaction of salicylic acid and acetic acid in the presence of phosphoric acid. Phosphoric acid acts as a catalyst and fastens the speed of reaction. It protonates the carboxyl group of salicylic acid and favors the esterficiation reaction.

To prepare aspirin, salicylic acid is reacted with an excess of acetic anhydride. A small amount of a strong acid is used as a catalyst which speeds up the reaction. In this experiment, phosphoric acid will be used as the catalyst. The excess acetic acid will be quenched with the addition of water.