Mechanism of aspirin by salicyclic acid reacts with acetic acid ? Mechanism of benzoic acid from benzamide?

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Explanation:

The synthesis of aspirin is shown in the reaction scheme attached to this answer. The production of aspirin involves the reaction of acetyl salicyclic acid and acetic anhydride. HA in the reaction mechanism refers to an acid that is used in the reaction

Similarly  benzamide, is converted to the carbonyl carbocation by reaction with acid. The -NH2 group is protonated and subsequently departs as a leaving group. An OH^- completes the mechanism forming a carboxylic acid. The movement of electrons is shown in the image attached.

Again, the diazotization of benzamide using sodium nitrate and concentrated HCl yields benzene diazonium chloride. Addition of water to benzene diazonium chloride yields the benzoic acid and nitrogen gas.