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.

The sequence from the following that would result in giving predominantly 3, 4, 5-Tribromoaniline… (JEE Main 2025) | Canvas Classes