Question

Write down the product compound for the following reaction:

• A. Phenylacetic acid salt (Potassium phenylacetate, \( C_6H_5CH_2COOK \))
• B. Benzoic acid salt (Potassium benzoate, \( C_6H_5COOK \))
• C. Phenyl acetone
• D. Benzaldehyde

Hint:

It doesn't matter if the side chain is Methyl, Ethyl, or Isobutyl; if it has a benzylic hydrogen, $KMnO_4$ turns it into a $-COOK$ (or $-COOH$ after acidification) group. Note: Tertiary butyl groups ($no$ benzylic H) will $not$ react this way!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:

• An alkylbenzene with a benzylic hydrogen is treated with hot alkaline \( KMnO_4 \). We need the product.

Step 2: Detailed Explanation:

• Hot alkaline \( KMnO_4 \) oxidises any alkyl side chain that has at least one benzylic hydrogen completely to a carboxylate group attached directly to the ring, irrespective of the length of the chain.

• The whole side chain is cut down to the benzylic carbon, which becomes \( -COOK \).

• The product is therefore potassium benzoate, \( C_6H_5COOK \) (it gives benzoic acid on acidification).

• Phenylacetate, phenyl acetone and benzaldehyde would need milder or partial oxidation and are not formed.

Step 3: Final Answer:
The correct option is (B) benzoic acid salt (potassium benzoate).