Question

Explain why it is necessary to quench the reaction (add hot water) at the end of the aspirin experiment. Please include a reaction scheme in your answer.

- for this question I'm guessing one would quench as to not crash the aspirin out of solution as a precipitate. But I dont know how I would draw this reaction scheme. Thank you in advance

Answer 1

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. The aspirin product is not very soluble in water so the aspirin product will precipitate when water is added. The synthesis reaction of aspirin is shown below

salicylic acid (C₇H₆O₃) + acetic anhydride (C₄H₆O₃) → acetylsalicylic acid (C₉H₈O₄) + acetic acid (C₂H₄O₂)

At higher temperatures (warm water), molecules have more kinetic energy and collide with each other more often to interact with water molecules, increasing the solubility of the aspirin.