Question

Predict the major product (P) in the following reaction:

• A. (A) a ketone with a sulfonic acid group attached to the phenyl ring
• B. (B) a polyaromatic ketone bearing a chlorophenyl side chain
• C. (C) a simple benzophenone derivative formed by intramolecular Friedel–Crafts acylation
• D. (D) a chlorinated polyaromatic ketone with an external phenyl substituent

Answer 1

Answer: (C)

a simple benzophenone derivative formed by intramolecular Friedel–Crafts acylation

Answer 2

Step 1: Conversion of –COOH to –COCl

Step 2: Intramolecular Friedel–Crafts acylation

• AlCl₃ activates the acyl chloride.
• The central ring undergoes electrophilic attack by the acylium ion.
• A new C–C bond forms, closing a ketone-containing ring.

Key points:

• PCl₅ efficiently converts carboxylic acids to acyl chlorides.
• Intramolecular acylation is favored when a suitably positioned aromatic ring can cyclize.
• No external chlorination or sulfonation occurs under these conditions.