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Question

Question: Choose the correct set of reagents for the following conversion. ...

Choose the correct set of reagents for the following conversion.

A

Cl2/Fe; Br2/anhy.AlCl3; aq. KOH

B

Cl2/anhy.AlCl3; Br2/Fe; alc. KOH

C

Br2/Fe: Cl2, Δ; alc.KOH

D

Br2/anhy.AlCl3; Cl2, Δ; aq. KOH

Answer

Br2/Fe: Cl2, Δ; alc.KOH

Explanation

Solution

The correct sequence of reactions is:

  1. Aromatic Bromination: Use Br₂/Fe to carry out electrophilic substitution on ethylbenzene. The ethyl group is ortho/para directing, so the bromine gets installed at the para position.

  2. Benzylic Halogenation: Next, treat the resulting p-bromoethylbenzene with Cl₂ under thermal (Δ) conditions. This free radical process selectively substitutes one hydrogen at the benzylic methylene, forming a benzylic chloride.

  3. Dehydrohalogenation: Finally, treat the benzylic chloride with alcoholic KOH. The base induces elimination (E2) of HCl from the side chain to form the vinyl group, yielding the final brominated styrene derivative.