The sequence from the following that would result in giving predominantly 3, 4, 5-Tribromoaniline is:
Amines · Class 12 · JEE Main Previous Year Question
The sequence from the following that would result in giving predominantly 3, 4, 5-Tribromoaniline is:
- a
Reaction (a)
- b
Reaction (b)
- c✓
Reaction (c)
- d
Reaction (d)
Reaction (c)
Step 1 — Target molecule: 3,4,5-tribromoaniline
We need at position 1 and at positions 3, 4, and 5.
Step 2 — Analyse option (c) — 4-nitroaniline route
Starting material: 4-nitroaniline ( at C1, at C4)
Step (i): Bromination with (excess)/acetic acid
is a strong o/p director. Bromination occurs at positions 2, 3, 5, 6 (ortho and para to ). With excess , positions 2, 3, 5, 6 are brominated. But at C4 blocks C4. Result: 2,3,5,6-tetrabromo-4-nitroaniline.
Step (ii): (diazotization) converts to , then (Sandmeyer) replaces with at C1.
Step (iii): reduces at C4 back to .
Result: at C4, 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 at the correct position, ultimately yielding 3,4,5-tribromoaniline.
Key Points to Remember:
- is a powerful o/p director — direct bromination of aniline gives 2,4,6-tribromoaniline
- To get 3,4,5-tribromo pattern, protect and use directing effects
- Sandmeyer reaction: $\ce{ArN2^+Cl^- + CuBr -> ArBr + N2 + CuCl}
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