JEE Main 2025 Jan 24 Shift 2, Chemistry Q3: Preparation of Alkyl Halides (Halo Alkanes) & Aryl Halides (Halo Arenes)

JEE Main2025Jan 24, Shift 2Chemistry

For reaction

The correct order of set of reagents for the above conversion is :

A
$B r_{2} ∣ F e B r_{3}, H_{2} O (Δ), N a O H$
B
$H_{2} S O_{4}, A c_{2} O, B r_{2}, H_{2} O (Δ), N a O H$
C
$A c_{2} O, B r_{2}, H_{2} O (Δ), N a O H$
D
$A c_{2} O, H_{2} S O_{4}, B r_{2}, N a O H$

Solution

The goal is to install bromine selectively at the ortho position of aniline. Direct bromination of aniline gives 2,4,6-tribromoaniline because the $- N H_{2}$ group is too strongly activating, so the $- N H_{2}$ has to be tamed and the para position has to be blocked.

$H_{2} S O_{4}$ (conc.): sulfonation of aniline at the para position gives sulfanilic acid, blocking the para site.
$A c_{2} O$ : acetylation of the amino group gives an acetanilide-type nitrogen, which is far less activating and stops poly-bromination.
$B r_{2}$ : monobromination now occurs cleanly at the free ortho position.
$H_{2} O, Δ$ : hydrolysis removes the $- S O_{3} H$ blocking group.
$N a O H$ (basic hydrolysis): cleaves the acetamide back to the free $- N H_{2}$ , giving 2-bromoaniline as the major product.

Correct option: (2)

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JEE Main 2025 Jan 24 Shift 2, Chemistry Q3: Preparation of Alkyl Halides (Halo Alkanes) & Aryl Halides (Halo Arenes)

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