Read the passage given and answer the question.
Phenol and alcohol have the same functional group (-OH) but phenols are stronger acids than alcohols due to the resonance stabilization of phenoxide ion than alkoxide ion \((-RO^-)\). Electron withdrawing groups tend to increase the acidic strength while electron releasing groups tend to decrease it.
Identify the product of the given reaction:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Salicylaldehyde
Phenol heated with chloroform and aqueous NaOH, followed by acidification, is the Reimer-Tiemann reaction. Dichlorocarbene (:\( \ce{CCl2} \)), formed from \( \ce{CHCl3} \) and the base, attacks the phenoxide ion at the ortho position. The –\( \ce{CHCl2} \) group so introduced is hydrolysed by the alkali to –CHO, and acid (\( \ce{H^{+}} \)) frees the phenol:
\( \ce{C6H5OH} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CHCl3}\text{ + aq. NaOH}} \text{o-}\ce{HOC6H4CHO} \)
The product, 2-hydroxybenzaldehyde, is salicylaldehyde.
Why the other options are incorrect
Option (1) o-Chlorophenol — Incorrect. Chlorine does not stay on the ring; the carbon of \( \ce{CHCl3} \) is introduced and becomes the –CHO group.
Option (2) Benzene — Incorrect. Phenol is converted to benzene only by heating with zinc dust, not by \( \ce{CHCl3} \)/NaOH.
Option (3) Dichlorophenol — Incorrect. No ring chlorination takes place; the dichloromethyl group formed first is hydrolysed to an aldehyde group.
NCERT (2026-27 edition):
Reimer-Tiemann Reaction
