Question

The compound which does not lead to benzoic acid by oxidation with KMnO$_4$ is

• A. toluene
• B. benzyl alcohol
• C. $n$-butylbenzene
• D. $t$-butylbenzene
• E. styrene

Hint:

Rule: Benzylic hydrogen present ⇒ oxidation to benzoic acid. No benzylic hydrogen ⇒ no reaction with \( KMnO_4 \).

Answer 1

The Correct Option is D

Concept: Hot \( KMnO_4 \) oxidizes any alkyl side chain on benzene to benzoic acid, provided there is at least one benzylic hydrogen. If no benzylic hydrogen is present, oxidation does not occur.

Step 1: {Check each compound for benzylic hydrogen.}
(A) Toluene (\( -CH_3 \))
Has benzylic H \( \Rightarrow \) gives benzoic acid ✔ (B) Benzyl alcohol (\( -CH_2OH \))
Has benzylic H \( \Rightarrow \) gives benzoic acid ✔ (C) \( n \)-butylbenzene (\( -CH_2CH_2CH_2CH_3 \))
Has benzylic \( CH_2 \) \( \Rightarrow \) gives benzoic acid ✔ (D) \( t \)-butylbenzene (\( -C(CH_3)_3 \))
No benzylic hydrogen \( \Rightarrow \) no oxidation ✖ (E) Styrene (\( -CH=CH_2 \))
Has benzylic hydrogen \( \Rightarrow \) oxidizes to benzoic acid ✔

Step 2: {Conclusion.}
Only the compound without benzylic hydrogen does not give benzoic acid.

Step 3: {Final answer.}
\[ \boxed{\text{(D) } t\text{-butylbenzene}} \]