Question

How will you convert nitrobenzene to 2, 4, 6-Tribromo aniline?

Hint:

The amino group is such a strong activator that you don't need a Lewis acid catalyst for bromination; bromine water alone is enough to triple-substitute!

Answer 1

Concept:
This conversion requires two distinct chemical transformations:

1. Reduction of the nitro group (-NO₂) to an amino group (-NH₂).
2. Electrophilic aromatic substitution to add three bromine atoms.

Step 1: Reduction to Aniline.
Nitrobenzene is reduced using tin and hydrochloric acid (Sn/HCl) or iron and hydrochloric acid (Fe/HCl).
C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2 H₂O

Step 2: Bromination of Aniline.
Aniline is highly reactive due to the resonance effect of the -NH₂ group. Treating it with bromine water (Br₂/H₂O) results in instantaneous substitution at all available ortho and para positions.
C₆H₅NH₂ + 3 Br₂ → 2,4,6-Tribromoaniline ↓ (white ppt) + 3 HBr