Name the reaction when Benzene is treated with ethanoyl chloride in the presence of anhydrous \( \text{AlCl}_3 \)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Friedel Crafts Acylation
In a Friedel-Crafts reaction a group is put onto a benzene ring by electrophilic substitution, with anhydrous \( \ce{AlCl3} \) as the Lewis acid catalyst. The name depends on what is put on: an alkyl group from an alkyl halide (alkylation) or an acyl group, R–CO–, from an acid chloride or anhydride (acylation).
Ethanoyl chloride, \( \ce{CH3COCl} \), is an acid chloride. \( \ce{AlCl3} \) takes the chloride from it and gives the electrophile, the acylium ion \( \ce{CH3CO+} \), which attacks the benzene ring; loss of \( \ce{H+} \) restores the ring. The product is a ketone, acetophenone (1-phenylethanone):
\( \displaystyle \ce{CH3COCl + AlCl3 -> CH3CO+ + AlCl4^-} \)
\( \displaystyle \ce{C6H6 + CH3COCl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{C6H5COCH3 + HCl} \)
So the reaction is Friedel-Crafts acylation.
Why the other options are incorrect
Option (1) Friedel Crafts Alkylation — Incorrect. It uses an alkyl halide and puts an alkyl group on the ring, for example \( \ce{C6H6 + CH3Cl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{C6H5CH3 + HCl} \); ethanoyl chloride puts on an acyl group instead.
Option (3) Chlorination — Incorrect. Chlorination of benzene uses \( \ce{Cl2} \) with anhydrous \( \ce{FeCl3} \) and gives chlorobenzene; here the chlorine of ethanoyl chloride leaves as HCl and no chlorine enters the ring.
Option (4) Benzoylation — Incorrect. Benzoylation introduces the benzoyl group, \( \ce{C6H5CO-} \), using benzoyl chloride; ethanoyl chloride introduces the ethanoyl (acetyl) group.
NCERT (2026-27 edition):
From Benzene or Substituted Benzenes
