JEE Main · 2024 · 29 Jan 2024 · Shift 2 · Alcohols Phenols and Ethers

Treating phenol with chloroform and NaOH is the Reimer–Tiemann reaction. Base first deprotonates phenol to the more nucleophilic phenoxide ion; hydroxide also deprotonates $\mathrm{CHC}{\mathrm{l}}_3$, which undergoes $\alpha$-elimination to generate dichlorocarbene, $:\mathrm{CC}{\mathrm{l}}_2$, a strong electrophile.

The phenoxide ring, activated and ortho/para-directed by the oxygen, attacks the carbene predominantly at the ortho position, giving a benzylic $-\mathrm{CHC}{\mathrm{l}}_2$ group on the ring next to $-{\mathrm{O}}^{-}$. Acidic hydrolysis then converts this dichloromethyl group into an aldehyde:


The product is 2-hydroxybenzaldehyde (salicylaldehyde).