Aniline is a catalyst in the reaction. The acetic anhydride to be added later will react in a dangerously exothermic fashion if added to water only. Draw the structure of this by-product. In the acetylation of aniline, aniline is dissolved in dilute HCl as its hydrochloride salt. Acetic anhydride is then added and immediately afterward a solution of sodium acetate is added.
Sodium acetate protonates the nitrogen of aniline so that it is soluble in water.
Sodium acetate produces an equilibrium concentration of aniline having a deprotonated nucleophilic nitrogen. Sodium acetate is the source of the acetyl protecting group that is introduced onto the nitrogen of aniline. Sodium acetate prevents hydrolysis of acetic anhydride. Sodium acetate reacts with acetic anhydride to produce acetic anhydride. Explain why the p-acetamidobenzenesulfonyl chloride that you prepared had to be converted to the sulfonamide with ammonia in the same lab period and not the following week.