Identify the name reaction:

The correct answer is Option (4) → Kolbe's reaction

Phenol is converted by NaOH into sodium phenoxide. The phenoxide ion is even more reactive than phenol towards electrophilic substitution, so it reacts with carbon dioxide, a weak electrophile; acidification then gives ortho-hydroxybenzoic acid (salicylic acid) as the main product. This is Kolbe’s reaction.

    \( \ce{C6H5OH} \xrightarrow{\ce{NaOH}} \ce{C6H5ONa} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CO2}} \underset{\text{salicylic acid}}{\ce{HOC6H4COOH}} \)

Why the other options are incorrect

• Option (1) Reimer-Tiemann reaction — Incorrect. Phenol is treated with chloroform and NaOH, and a –CHO group is introduced (salicylaldehyde), not –COOH from \( \ce{CO2} \).

• Option (2) Oxidation — Incorrect. No oxidising agent is used. \( \ce{CO2} \) acts as an electrophile and puts a –COOH group on the ring by electrophilic substitution of the phenoxide ion.

• Option (3) Williamson synthesis — Incorrect. An alkyl halide reacts with sodium alkoxide or phenoxide to give an ether.

NCERT (2026-27 edition):
Kolbe’s Reaction

Note: The same/similar question has been asked in different years by NTA as per the details given below: