Answer the question on the basis of passage given below:
Strong oxidizing agents, oxidize toluene and its derivatives to benzoic acid. However, it is possible to stop the oxidation at the aldehyde stage with suitable reagents that convert methyl group to an intermediate that is difficult to oxidize further.
A here is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → No reaction
Side-chain oxidation of an alkylbenzene by \( \ce{KMnO4} \) or chromic acid starts at the benzylic C–H bond (the carbon attached to the ring). Primary and secondary alkyl groups have such a hydrogen and are oxidised right down to –COOH.
The compound here is tert-butylbenzene, \( \ce{C6H5C(CH3)3} \). Its benzylic carbon carries three methyl groups and no hydrogen, so the side chain is not attacked: a tertiary alkyl group is not affected, and there is no reaction. Compare toluene, which has benzylic hydrogens:
\( \ce{C6H5CH3} \xrightarrow[\text{(ii) }\ce{H3O+}]{\text{(i) }\ce{KMnO4-KOH}, \Delta} \ce{C6H5COOH} \)
Why the other options are incorrect
Option (1) Benzoic acid — Incorrect. This forms from toluene, ethylbenzene and other alkylbenzenes with a benzylic hydrogen, not from a tert-butyl group.
Option (2) 2-Methyl-2-phenylpropanoic acid — Incorrect. This would need one methyl group to be oxidised while the quaternary carbon stays; oxidation does not start at a methyl group away from the ring.
Option (4) the tricarboxylic acid — Incorrect. Oxidising all three methyl groups to –COOH is not what happens with these reagents; the tert-butyl group is not attacked at all.
NCERT (2026-27 edition):
From Alkylbenzenes
