Phenol: Esterification, Etherification, Aspirin Synthesis, Oxidation and Reduction (JEE Advanced)

“Esterification; Etherification; Aspirin synthesis; Oxidation and reduction reactions of phenol”

Source: JEE Advanced 2026 Information Bulletin, Annexure-I. Closest JEE Main topic: Electrophilic substitution reactions, halogenation, nitration and sulphonation, Reimer - Tiemann reaction.

JEE Main focuses on electrophilic substitution reactions of phenol like halogenation and nitration, but Advanced expects you to know its reactions with acyl chlorides, ethers formation via Williamson synthesis, and redox behavior. Aspirin synthesis is a classic named reaction that appears frequently in Advanced.

• Phenol does not esterify easily with carboxylic acids because the phenoxide ion is a poor nucleophile and the reaction is reversible. Acyl chlorides or acid anhydrides are used instead.
• Esterification of phenol: Phenol + Acetyl chloride → Phenyl acetate + HCl. This reaction is called Schotten-Baumann reaction when done in presence of NaOH.
• Etherification: Phenol cannot undergo acid-catalyzed etherification like alcohols. Williamson synthesis is used: Phenoxide ion + Alkyl halide → Phenyl alkyl ether.
• Aspirin synthesis: Salicylic acid (2-hydroxybenzoic acid) + Acetic anhydride → Aspirin (acetylsalicylic acid) + Acetic acid. The phenolic OH gets acetylated.
• Oxidation of phenol: With chromic acid gives benzoquinone. With air and enzymes gives colored products (why phenol turns pink on standing).
• Reduction of phenol: Catalytic hydrogenation (Ni, high pressure and temperature) converts phenol to cyclohexanol. Birch reduction gives cyclohexenol.

• C₆H₅OH + CH₃COCl → C₆H₅OCOCH₃ + HCl (Phenyl acetate formation)
• C₆H₅O⁻Na⁺ + R-X → C₆H₅-O-R + NaX (Williamson synthesis for phenyl ethers)
• 2-HOC₆H₄COOH + (CH₃CO)₂O → 2-CH₃COOC₆H₄COOH + CH₃COOH (Aspirin synthesis)
• C₆H₅OH + [O] (chromic acid) → O=C₆H₄=O (Benzoquinone)
• C₆H₅OH + 3H₂ (Ni, Δ, pressure) → C₆H₁₁OH (Cyclohexanol)
• Phenol + (CH₃CO)₂O + NaOH → Phenyl acetate (milder than acid chloride method)
• Phenoxide ion is a weaker nucleophile than alkoxide due to resonance stabilization

• Trying to esterify phenol with carboxylic acid and mineral acid catalyst like you do with alcohols. This does not work well for phenol.
• Confusing aspirin structure: the acetyl group is on the phenolic OH, not on the carboxylic acid group. Salicylic acid has both groups, only the OH reacts.
• Using phenol directly in Williamson synthesis instead of converting it to phenoxide first. Phenol itself is not nucleophilic enough.
• Forgetting that oxidation of phenol gives quinone (a diketone), not a carboxylic acid. The ring structure changes significantly.

Question. An organic compound A (C₇H₆O₃) gives effervescence with NaHCO₃ and also gives violet color with FeCl₃. When A is treated with acetic anhydride in presence of a few drops of concentrated H₂SO₄, compound B (C₉H₈O₄) is formed. Identify A and B, and write the reaction.

Solved twice independently; both solutions agree.