Identify "Y" in the following reaction:

The correct answer is Option (1) → Benzaldehyde

Chlorine reacts with toluene in two different ways. With a Lewis acid such as \( \ce{FeCl3} \) in the dark it substitutes on the ring. In sunlight (hν), without a catalyst, chlorine splits into free radicals, which attack the methyl side chain instead. Chlorination continues on the same carbon, and with enough chlorine two hydrogens of the methyl group are replaced, giving benzal chloride (X):

    \( \displaystyle \ce{C6H5CH3 + 2Cl2} \xrightarrow{h\nu} \ce{C6H5CHCl2 + 2HCl} \)

A carbon carrying two chlorine atoms is hydrolysed by water at 373 K to an unstable gem-diol, which loses water to give the aldehyde. This is a commercial method for making benzaldehyde (Y):

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

    \( \displaystyle [\ce{C6H5CH(OH)2}] \xrightarrow{-\ce{H2O}} \ce{C6H5CHO} \)

So Y is benzaldehyde.

Why the other options are incorrect

• Option (2) 2-Methylbenzaldehyde — Incorrect. It would need a new –CHO group on the ring while the methyl group stayed; in light, chlorine attacks the side chain, which itself becomes the –CHO group.

• Option (3) 2-Chlorophenol — Incorrect. Ring chlorination needs a Lewis acid such as \( \ce{FeCl3} \) in the dark, and an aryl chloride is not hydrolysed by water at 373 K; it needs NaOH at about 623 K and high pressure.

• Option (4) Benzal chloride — Incorrect. This is the intermediate X formed in the first step; water at 373 K converts it into benzaldehyde.

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

Note: The same/similar question has been asked in different years by NTA as per the details given below: