The reaction for the conversion of phenol into salicylic acid is known as
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Kolbe's reaction
Phenol is first converted by sodium hydroxide into sodium phenoxide. The phenoxide ion is even more reactive than phenol towards electrophilic substitution, so it reacts even with carbon dioxide, a weak electrophile. The carboxyl group enters mainly at the ortho position, and acidification gives ortho-hydroxybenzoic acid (salicylic acid). This is Kolbe’s reaction:
\( \displaystyle \ce{C6H5OH + NaOH -> C6H5ONa + H2O} \)
\( \displaystyle \ce{C6H5ONa} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CO2}} o\text{-}\ce{HOC6H4COOH} \)
Why the other options are incorrect
Option (1) Reimer-Tiemann reaction — Incorrect. Phenol reacts with chloroform and NaOH and gives salicylaldehyde (a –CHO group at the ortho position), not salicylic acid:
\( \displaystyle \ce{C6H5OH} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CHCl3},\ \text{aq. }\ce{NaOH}} o\text{-}\ce{HOC6H4CHO} \)
Option (3) Claisen-condensation reaction — Incorrect. Two molecules of an ester with α-hydrogens condense in the presence of a base such as sodium ethoxide to give a β-keto ester; phenol and \( \ce{CO2} \) play no part in it:
\( \displaystyle \ce{2CH3COOC2H5} \xrightarrow{\ce{C2H5ONa}} \ce{CH3COCH2COOC2H5 + C2H5OH} \)
Option (4) Etard reaction — Incorrect. Toluene is oxidised by chromyl chloride (\( \ce{CrO2Cl2} \)) to a chromium complex, which is hydrolysed to benzaldehyde:
\( \displaystyle \ce{C6H5CH3} \xrightarrow[\text{(ii) }\ce{H3O+}]{\text{(i) }\ce{CrO2Cl2},\ \ce{CS2}} \ce{C6H5CHO} \)
NCERT (2026-27 edition):
Kolbe’s Reaction
