Reaction of phenol with chloroform in the presence of sodium hydroxide gives salicylaldehyde. The reaction is known as
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Reimer-Tiemann reaction
Phenol and its sodium salt (phenoxide) take part in several named reactions. They differ in the reagent and in what is put on the molecule:
Reimer–Tiemann reaction: phenol + chloroform + sodium hydroxide → a –CHO group at the ortho position (salicylaldehyde).
Kolbe’s reaction: sodium phenoxide + carbon dioxide under pressure, then acid → a –COOH group at the ortho position (salicylic acid).
Williamson synthesis: sodium alkoxide or phenoxide + alkyl halide → an ether.
With chloroform and sodium hydroxide, phenol reacts as the phenoxide ion; the product is first obtained as its sodium salt, and dilute acid sets free salicylaldehyde (2-hydroxybenzaldehyde):
\( \displaystyle \ce{C6H5OH + CHCl3 + 3NaOH} \xrightarrow{\text{340 K}} o\text{-}\ce{HOC6H4CHO} + \ce{3NaCl + 2H2O} \)
Option (2) Kolbe’s reaction — Incorrect. Sodium phenoxide is heated with carbon dioxide under pressure; the product is salicylic acid, not the aldehyde.
\( \displaystyle \ce{C6H5ONa + CO2} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) 400 K, 4-7 atm}} o\text{-}\ce{HOC6H4COOH} \)
Option (3) Williamson synthesis — Incorrect. An alkyl halide reacts with a sodium alkoxide or phenoxide to give an ether, for example anisole from sodium phenoxide and methyl iodide.
\( \displaystyle \ce{C6H5ONa + CH3I -> C6H5OCH3 + NaI} \)
Option (4) Claisen-Schmidt Condensation reaction — Incorrect. This is a cross aldol condensation of an aromatic aldehyde with a ketone in dilute alkali; no phenol or chloroform is used.
\( \displaystyle \ce{C6H5CHO + CH3COCH3} \xrightarrow{\text{dil. NaOH}} \ce{C6H5CH=CHCOCH3 + H2O} \)
NCERT (2026-27 edition):
Reimer-Tiemann Reaction
