Question

The compound(s), which give(s) benzoic acid on oxidation with KMnO$_4$, is (are) 

 

• A. A
• B. B
• C. C
• D. D

Hint:

Only aromatic side chains with at least one benzylic hydrogen (–CH$_2$– or –CH–) are oxidized to benzoic acid by KMnO$_4$.

Answer 1

The Correct Option is A, D

Step 1: Recall the oxidation property of KMnO$_4$.
Hot, acidic KMnO$_4$ oxidizes any alkyl side chain attached to an aromatic ring (Ar–R) to a carboxylic acid (Ar–COOH), provided there is at least one benzylic hydrogen.
Step 2: Analyze each compound.
(A) Contains a benzyl group (–CH$_2$–), hence oxidizes to benzoic acid.
(B) Contains a tertiary carbon without a benzylic hydrogen — no oxidation.
(C) Contains a biphenyl group — no benzylic position.
(D) Contains a benzylic –CH– group with hydrogen — oxidizes to benzoic acid.
Step 3: Conclusion.
The compounds (A) and (D) form benzoic acid on oxidation.