Bromination of aniline and how to stop at one Brऐनिलीन का ब्रोमीनन और एक Br पर कैसे रुकेंBromination of aniline and how to stop at one Br

Class 12 Chemistry · Chapter 9 · interactive diagram

Parts and what they mean

• Aniline (ऐनिलीन) — –NH₂ is a powerful activating, ortho/para-directing group.
• Bromine water, room temperature (ब्रोमीन जल, कक्ष ताप) — No catalyst is needed — the ring is that reactive.
• 2,4,6-Tribromoaniline — white precipitate (2,4,6-ट्राइब्रोमोऐनिलीन — श्वेत अवक्षेप) — All three o/p positions are substituted at once: C₆H₅NH₂ + 3Br₂ → C₆H₂Br₃NH₂ + 3HBr.
• Hydrogen bromide (3 mol) (हाइड्रोजन ब्रोमाइड (3 mol)) — One HBr for every H replaced by Br.
• Acetylation: acetic anhydride, pyridine (ऐसीटिलन: ऐसीटिक ऐनहाइड्राइड, पिरिडीन) — Protects the –NH₂ group as –NHCOCH₃.
• Acetanilide (–NHCOCH₃) (ऐसीटैनिलाइड (–NHCOCH₃)) — The N lone pair also interacts with the C=O oxygen by resonance, so it is less available to the ring → activating effect of –NHCOCH₃ is less than that of –NH₂.
• Br₂ in ethanoic acid (एथेनॉइक अम्ल में Br₂) — Brominates the moderately activated ring once, mainly at para.
• 4-Bromoacetanilide (major product) (4-ब्रोमोऐसीटैनिलाइड (मुख्य उत्पाद)) — Mono-substituted product.
• Hydrolysis of the amide (H⁺ or OH⁻) (ऐमाइड का जल-अपघटन (H⁺ या OH⁻)) — Removes the acetyl group and gives back –NH₂.
• 4-Bromoaniline (4-ब्रोमोऐनिलीन) — The monosubstituted aniline we wanted.

Steps

1. Protect: acetylate –NH₂ with acetic anhydride (pyridine) → acetanilide.
2. Brominate: Br₂ in CH₃COOH → mainly 4-bromoacetanilide (less activated ring, bulky group).
3. Deprotect: hydrolyse the amide (H⁺ or OH⁻) → 4-bromoaniline.

Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake