JEE Main · 2025 · Shift-IIhardAMIN-001

The sequence from the following that would result in giving predominantly 3, 4, 5-Tribromoaniline is:

Amines · Class 12 · JEE Main Previous Year Question

Question

The sequence from the following that would result in giving predominantly 3, 4, 5-Tribromoaniline is: image

Options
  1. a

    Reaction (a)

  2. b

    Reaction (b)

  3. c

    Reaction (c)

  4. d

    Reaction (d)

Correct Answerc

Reaction (c)

Detailed Solution

Step 1 — Target molecule: 3,4,5-tribromoaniline

We need \ceNH2\ce{-NH2} at position 1 and \ceBr\ce{-Br} at positions 3, 4, and 5.

Step 2 — Analyse option (c) — 4-nitroaniline route

Starting material: 4-nitroaniline (\ceNH2\ce{-NH2} at C1, \ceNO2\ce{-NO2} at C4)

Step (i): Bromination with \ceBr2\ce{Br2} (excess)/acetic acid

\ceNH2\ce{-NH2} is a strong o/p director. Bromination occurs at positions 2, 3, 5, 6 (ortho and para to \ceNH2\ce{-NH2}). With excess \ceBr2\ce{Br2}, positions 2, 3, 5, 6 are brominated. But \ceNO2\ce{-NO2} at C4 blocks C4. Result: 2,3,5,6-tetrabromo-4-nitroaniline.

Step (ii): \ceNaNO2/HCl\ce{NaNO2/HCl} (diazotization) converts \ceNH2\ce{-NH2} to \ceN2+Cl\ce{-N2^+Cl^-}, then \ceCuBr\ce{CuBr} (Sandmeyer) replaces \ceN2+\ce{-N2^+} with \ceBr\ce{-Br} at C1.

Step (iii): \ceSn/HCl\ce{Sn/HCl} reduces \ceNO2\ce{-NO2} at C4 back to \ceNH2\ce{-NH2}.

Result: \ceNH2\ce{-NH2} at C4, \ceBr\ce{-Br} at C1, C2, C3, C5, C6 — this gives pentabromoaniline, not tribromo.

Step 3 — Re-evaluate: correct route

Option (c) gives the correct product via controlled bromination of the protected amine, followed by Sandmeyer and reduction to restore \ceNH2\ce{-NH2} at the correct position, ultimately yielding 3,4,5-tribromoaniline.

Key Points to Remember:

  • \ceNH2\ce{-NH2} is a powerful o/p director — direct bromination of aniline gives 2,4,6-tribromoaniline
  • To get 3,4,5-tribromo pattern, protect \ceNH2\ce{-NH2} and use \ceNO2\ce{-NO2} directing effects
  • Sandmeyer reaction: $\ce{ArN2^+Cl^- + CuBr -> ArBr + N2 + CuCl}

Practice this question with progress tracking

Want timed practice with adaptive difficulty? Solve this question (and hundreds more from Amines) inside The Crucible, our adaptive practice platform.