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Question:

How can the following conversion be carried out:(i) Aniline to bromobenzene (ii) Chlorobenzene to 2-chloroaccetophenone (iii) Chloroethane to butane

Solution:

(i) Aniline to bromobenzene:
Aniline is first diazotized using NaNO2 and HCl at low temperature (0-5°C) to form benzenediazonium chloride. This is then treated with HBr/CuBr (Sandmeyer's reaction) to form bromobenzene.

(ii) Chlorobenzene to 2-chloroacetophenone:
Chlorobenzene undergoes Friedel-Crafts acylation with acetyl chloride (CH3COCl) in the presence of anhydrous aluminum chloride (AlCl3) as a catalyst. The acetyl group is added to the ring, specifically to the position ortho to the chloro group (2-chloroacetophenone). The reaction proceeds through a carbocation intermediate. This is an electrophilic aromatic substitution.

(iii) Chloroethane to butane:
Chloroethane is first treated with sodium metal in dry ether (Wurtz reaction). This reaction involves a coupling reaction of two alkyl halides to form a longer chain alkane. Two molecules of chloroethane react with two sodium atoms, resulting in the formation of butane and sodium chloride as a byproduct. This is an example of a reductive coupling reaction.

Reactions Summary:

(i) Aniline + NaNO2 + HCl → Benzenediazonium chloride
Benzenediazonium chloride + HBr/CuBr → Bromobenzene

(ii) Chlorobenzene + CH3COCl + AlCl3 → 2-chloroacetophenone + HCl

(iii) 2 Chloroethane + 2Na(Dry Ether) → Butane + 2NaCl