In the Reimer–Tiemann reaction, phenol is treated with chloroform in…

The correct answer is Option (2) → A substituted benzal chloride; salicylaldehyde

• In the Reimer–Tiemann reaction, chloroform and sodium hydroxide introduce a –CHO group at the ortho position of the benzene ring of phenol.

• The carbon of CHCl₃ first enters the ring as a –CHCl₂ group, giving a substituted benzal chloride. The alkali then hydrolyses the two chlorine atoms on this one carbon, and the –CHCl₂ group becomes –CHO:

      \( \displaystyle \ce{C6H5OH} \xrightarrow{\ce{CHCl3} + \text{aq. } \ce{NaOH}} \underset{\text{substituted benzal chloride}}{\ce{C6H4(ONa)CHCl2}} \xrightarrow{\text{hydrolysis}} \underset{\text{salicylaldehyde}}{\ce{C6H4(OH)CHO}} \)

• The product, salicylaldehyde, is 2-hydroxybenzaldehyde.

Why the other options are incorrect

Option (1) A substituted benzyl chloride; salicylaldehyde — Incorrect. A benzyl chloride has a –CH₂Cl group with only one chlorine. The intermediate here carries –CHCl₂, two chlorines on one carbon, which is what turns into –CHO on hydrolysis.

Option (3) A substituted benzal chloride; salicylic acid — Incorrect. Salicylic acid (2-hydroxybenzoic acid) is the product of Kolbe’s reaction, in which phenoxide reacts with carbon dioxide; chloroform gives an aldehyde group, not a carboxyl group.

Option (4) A substituted benzyl chloride; salicylic acid — Incorrect. Both parts are wrong: the intermediate has a –CHCl₂ group, and the product is an aldehyde, not a carboxylic acid.

NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “3. Reimer-Tiemann reaction
On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann reaction.”

“The intermediate substituted benzal chloride is hydrolysed in the presence of alkali to produce salicylaldehyde.”