Identify the major product Y in the following reaction.

The correct answer is Option (3) → benzaldehyde

In the presence of light (and no catalyst), chlorine attacks the side chain of toluene, not the ring. This is a free radical substitution, and the methyl hydrogens are replaced one after another:

    \( \displaystyle \ce{C6H5CH3 + Cl2} \xrightarrow{h\nu} \ce{C6H5CH2Cl + HCl} \)

    \( \displaystyle \ce{C6H5CH2Cl + Cl2} \xrightarrow{h\nu} \ce{C6H5CHCl2 + HCl} \)

    \( \displaystyle \ce{C6H5CHCl2 + Cl2} \xrightarrow{h\nu} \ce{C6H5CCl3 + HCl} \)

The dichloro compound, benzal chloride (C₆H₅CHCl₂), is X. On hydrolysis with water at 373 K both Cl atoms are replaced by OH. The resulting gem-diol (two OH groups on one carbon) is unstable and loses water to give an aldehyde:

    \( \displaystyle \ce{C6H5CHCl2 + 2H2O} \xrightarrow{373\ \mathrm{K}} \ce{C6H5CH(OH)2 + 2HCl} \)

    \( \displaystyle \ce{C6H5CH(OH)2 -> C6H5CHO + H2O} \)

So Y is benzaldehyde.

Why the other options are incorrect

• Option (1) benzal chloride (C₆H₅CHCl₂) — Incorrect. This is the intermediate X, not the hydrolysis product Y.

• Option (2) benzotrichloride (C₆H₅CCl₃) — Incorrect. This is the fully chlorinated side chain; its hydrolysis would give benzoic acid, not an aldehyde.

      \( \displaystyle \ce{C6H5CCl3 + 2H2O -> C6H5COOH + 3HCl} \)

• Option (4) benzyl chloride (C₆H₅CH₂Cl) — Incorrect. This is the monochloro compound; its hydrolysis would give benzyl alcohol.

      \( \displaystyle \ce{C6H5CH2Cl + H2O -> C6H5CH2OH + HCl} \)

NCERT (2026-27 edition):
By Side Chain Chlorination Followed by Hydrolysis