Question

The structures of A and B formed in the following reaction are : [Ph = \(-C_6H_5\)] 

• A. A
• B. B
• C. C
• D. D

Hint:

Friedel-Crafts acylation with cyclic anhydrides is a classic method for extending the carbon chain on a benzene ring. Remember: Step 1 adds the chain with a \(C=O\), and Step 2 (Clemmensen or Wolff-Kishner) removes the oxygen.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The sequence consists of a Friedel-Crafts acylation with a cyclic anhydride, followed by a Clemmensen reduction.
Step 2: Detailed Explanation:
1. Formation of A: Benzene reacts with succinic anhydride in the presence of \(AlCl_3\) (a Lewis acid catalyst). The anhydride ring opens, and the acyl group attaches to the benzene ring. The final product of this acylation step is 4-phenyl-4-oxobutanoic acid (\(Ph-CO-CH_2-CH_2-COOH\)).
2. Formation of B: The keto-acid \(A\) is treated with zinc amalgam (\(Zn/Hg\)) and concentrated hydrochloric acid (\(HCl\)). This is the Clemmensen reduction, which specifically reduces the carbonyl group (\(C=O\)) of ketones or aldehydes to a methylene group (\(CH_2\)).
\[ Ph-CO-CH_2-CH_2-COOH \xrightarrow{Zn/Hg, HCl} Ph-CH_2-CH_2-CH_2-COOH \]
The product \(B\) is 4-phenylbutanoic acid.
Step 3: Final Answer:
Structure A is the \(\gamma\)-keto acid and B is the saturated fatty acid derivative, as shown in option (A).