Question

The correct sequence of reagents to be added for the following conversion is:

• A. Br\(_2\)/Fe; alc. KOH; Cl\(_2\)/FeCl\(_3\)
• B. Br\(_2\)/FeCl\(_3\); Cl\(_2\)/\(\Delta\); alc. KOH
• C. FeCl\(_3\)/Br\(_2\); alc. KOH; H\(^+\)/\(\Delta\)
• D. Cl\(_2\)/FeCl\(_3\); Br\(_2\)/FeCl\(_3\); alc. KOH

Hint:

The sequence of reactions involving bromination, chlorination, and dehydrohalogenation (with alc. KOH) is a typical method for forming alkenes (like styrene) from alkyl-substituted benzenes.

Answer 1

The Correct Option is B

Step 1: Bromination with Br\(_2\)/FeCl\(_3\).
The first step involves the bromination of toluene (C\(_6\)H\(_5\)CH\(_3\)) using bromine (Br\(_2\)) in the presence of ferric chloride (FeCl\(_3\)) as a catalyst.
This reaction replaces the methyl group (\(\text{-CH}_3\)) with a bromine atom, yielding bromotoluene.

Step 2: Chlorination with Cl\(_2\)/\(\Delta\).
Next, chlorination is carried out under heat (\(\Delta\)) to form benzyl chloride by introducing a chlorine atom onto the ring.
This is part of a typical halogenation in the presence of heat to form a vinyl group.

Step 3: Dehydrohalogenation with alc.
KOH.
Finally, the product undergoes a dehydrohalogenation reaction using alcoholic potassium hydroxide (alc.
KOH), which removes the hydrogen and halogen atoms from adjacent carbons in the benzyl group, leading to the formation of a vinyl group on the ring, resulting in styrene (C\(_6\)H\(_5\)CH=CH\(_2\)).