JEE Main · 2024 · 30 Jan 2024 · Shift 2 · Alcohols Phenols and Ethers

Phenol treated with chloroform and concentrated NaOH undergoes the Reimer–Tiemann reaction. Base deprotonates chloroform, and α-elimination of chloride from the resulting trichloromethyl carbanion generates the electrophilic intermediate dichlorocarbene, $:{\text{CCl}}_2$. The phenoxide ion, most nucleophilic at the ortho carbon, attacks this carbene; the resulting dichloromethyl adduct hydrolyses under the basic aqueous conditions to the aldehyde. ${\text{CO}}_2$/NaOH is the Kolbe–Schmidt carboxylation (gives salicylic acid) and ${\text{CCl}}_4$/NaOH does not generate a carbene that delivers an aldehyde. Phenol with ${\text{HCCl}}_3$, NaOH gives salicylaldehyde (2-hydroxybenzaldehyde).