To prepare monobromoaniline (specifically p-bromoaniline) from aniline without forming 2,4,6-tribromoaniline, how must the amino group (-NH2) be chemically protected prior to bromination?

Answer and explanation

Correct answer: D. By acetylating aniline to acetanilide with acetic anhydride to moderate amino group activation

  1. Step 1: In aniline, the group is a powerful activating group due to resonance, causing rapid polybromination with bromine water to give 2,4,6-tribromoaniline precipitate.
  2. Step 2: To obtain a mono-substituted product, the activating power of the group must be controlled (protected).
  3. Step 3: Aniline is reacted with acetic anhydride in pyridine to form acetanilide: .
  4. Step 4: In acetanilide, the nitrogen lone pair is shared by resonance with the carbonyl oxygen (), decreasing its electron donation into the benzene ring.
  5. Step 5: Electrophilic bromination of acetanilide with in acetic acid yields p-bromoacetanilide as the major product, which upon acidic or alkaline hydrolysis regenerates p-bromoaniline.
Answer
By acetylating aniline with acetic anhydride to form acetanilide, which moderates the activating effect of the amino group
Why not the others: 'By oxidizing aniline to nitrobenzene...' destroys the amino group; 'By methylating to a quaternary ammonium salt...' permanently blocks the nitrogen and imparts a deactivating positive charge; 'By dissolving in liquid bromine at 200°C' would destroy the molecule.

Practise more Organic Compounds Containing Nitrogen.

Free questions with an explanation for every one, and full timed NEET UG mock tests.

All Organic Compounds Containing Nitrogen questionsTake a mock test

More Organic Compounds Containing Nitrogen questions