Answer the question on the basis of passage given below:
Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group. The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group forms ethers.
Alcohols and phenols consist of two parts, an alkyl/aryl group and a hydroxyl group. The properties of alcohols and phenols are primarily due to the hydroxyl group. The nature of alkyl and aryl groups simply modifies these properties. Alcohols react both as nucleophiles and electrophiles whereas in phenols, the reactions that take place on the aromatic ring are electrophilic substitution reactions.
Name the given reaction:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Reimer-Tiemann reaction
The named reactions of phenols and related compounds in the options:
Reimer–Tiemann reaction: phenol + \( \ce{CHCl3} \) + aq. NaOH → a –CHO group enters the ortho position (via dichlorocarbene and a benzal chloride intermediate); acidification gives salicylaldehyde.
\( \ce{C6H5OH + CHCl3 + 3NaOH} \xrightarrow{\text{340 K}} \text{o-}\ce{NaOC6H4CHO + 3NaCl + 2H2O} \), then \( \xrightarrow{\ce{H+}} \text{o-}\ce{HOC6H4CHO} \)
Kolbe’s reaction: sodium phenoxide + \( \ce{CO2} \) (4–7 atm, 400 K), then acid → a –COOH group enters ortho: salicylic acid.
\( \ce{C6H5ONa + CO2 ->} \text{o-}\ce{HOC6H4COONa} \xrightarrow{\ce{H+}} \text{o-}\ce{HOC6H4COOH} \)
Williamson’s synthesis: an alkyl halide + sodium alkoxide/phenoxide → an ether.
\( \ce{R-X + R'-ONa -> R-O-R' + NaX} \)
Sandmeyer’s reaction: a diazonium salt + CuCl/HCl, CuBr/HBr or CuCN → an aryl halide or aryl cyanide.
\( \ce{C6H5N2+Cl-} \xrightarrow{\ce{CuCl/HCl}} \ce{C6H5Cl + N2} \)
The given conversion uses CHCl3 + aq. NaOH on phenol and gives the ortho-aldehyde, salicylaldehyde: the Reimer–Tiemann reaction.
NCERT (2026-27 edition):
Reimer-Tiemann Reaction
