Question

Benzene on reaction with benzoyl chloride in the presence of anhydrous \(\mathrm{AlCl}_3\) forms:

• A. Acetophenone
• B. Benzophenone
• C. Phenyl benzoate
• D. Benzoic anhydride

Hint:

For Friedel-Crafts acylation:
- Produces a ketone via an acylium ion.
- Requires an acyl chloride and \(\mathrm{AlCl}_3\).
- Distinguish from alkylation (uses alkyl halides).

Answer 1

The Correct Option is B

This is a Friedel-Crafts acylation reaction, where benzene (\(\mathrm{C}_6\mathrm{H}_6\)) reacts with benzoyl chloride (\(\mathrm{C}_6\mathrm{H}_5\mathrm{COCl}\)) catalyzed by \(\mathrm{AlCl}_3\) to form a ketone.
Step 1: Reaction mechanism - \(\mathrm{AlCl}_3\) coordinates with the oxygen of \(\mathrm{C}_6\mathrm{H}_5\mathrm{COCl}\), forming the acylium ion: \[ \mathrm{C}_6\mathrm{H}_5\mathrm{COCl} + \mathrm{AlCl}_3 \rightarrow \mathrm{C}_6\mathrm{H}_5\mathrm{CO}^+ + \mathrm{AlCl}_4^- \] - The acylium ion (\(\mathrm{C}_6\mathrm{H}_5\mathrm{CO}^+\)) attacks benzene’s pi system, forming a carbocation intermediate. - A proton is lost, restoring aromaticity, yielding the ketone.
Step 2: Product The reaction is: \[ \mathrm{C}_6\mathrm{H}_6 + \mathrm{C}_6\mathrm{H}_5\mathrm{COCl} \xrightarrow{\mathrm{AlCl}_3} \mathrm{C}_6\mathrm{H}_5\mathrm{COC}_6\mathrm{H}_5 + \mathrm{HCl} \] The product, \(\mathrm{C}_6\mathrm{H}_5\mathrm{COC}_6\mathrm{H}_5\), is benzophenone.
Step 3: Analyze options - (A) Acetophenone: \(\mathrm{C}_6\mathrm{H}_5\mathrm{COCH}_3\), from acetyl chloride (\(\mathrm{CH}_3\mathrm{COCl}\)). - (B) Benzophenone: \(\mathrm{C}_6\mathrm{H}_5\mathrm{COC}_6\mathrm{H}_5\), correct. - (C) Phenyl benzoate: An ester, not formed in acylation. - (D) Benzoic anhydride: \((\mathrm{C}_6\mathrm{H}_5\mathrm{CO})_2\mathrm{O}\), not a product.