2023 H2 Chem P1 Q25 — Carboxylic Acid Solution

The answer is D.
Ethanoyl chloride acylates the \(-\text{OH}\) group of 4-methylphenol: the phenol O atom, using a lone pair, attacks the electron-deficient carbonyl carbon and HCl is eliminated. The product is the ester 4-methylphenyl ethanoate, with \(-\text{OCOCH}_3\) para to the \(\text{CH}_3\) group, as drawn in D.
• A is wrong: it shows \(-\text{COCH}_3\) replacing an H on the methyl side chain; ethanoyl chloride does not substitute the C-H of an alkyl group.
• B is wrong: it shows \(-\text{COCH}_3\) on the ring next to the methyl group (ring acylation); this is Friedel-Crafts acylation, which needs a Lewis acid catalyst such as \(\text{AlCl}_3\), and the free \(-\text{OH}\) would react first.
• C is wrong: it shows \(-\text{COCH}_3\) where the \(-\text{OH}\) group was, so the OH has been lost; the C-O bond of a phenol has partial double bond character and is not broken in this reaction.