Aromatic Amines — Aniline and Diazonium Reactions

• Key reactions of aniline: acylation, benzoylation, sulphonation, and electrophilic substitution.
• Diazonium salts as synthetic intermediates: Sandmeyer reaction, Balz-Schiemann, azo coupling.
• Why −NH₂ is a strong ortho/para director: EAS on aniline.
• Converting diazonium salts to phenol, aryl halide, nitrile, and azo dye.

Level 1 — Reactions of aniline

Acylation: Aniline + (CH₃CO)₂O → acetanilide (N-phenylethanamide) + CH₃COOH. Used to protect −NH₂ group in synthesis (reduces reactivity, prevents over-substitution).

Benzoylation (Schotten-Baumann): Aniline + C₆H₅COCl / NaOH → benzanilide.

Sulphonation: Aniline (free base) with H₂SO₄ → anilinium sulphate (salt); on heating → sulphanilic acid (p-aminobenzenesulphonic acid) — internal salt (zwitterion). Basis of sulpha drugs.

Ring EAS: −NH₂ is strong ortho/para director (lone pair donation into ring). Aniline + Br₂/water (no catalyst) → 2,4,6-tribromoaniline (white precipitate, like phenol).

Reduction: Nitrobenzene + Sn/HCl → aniline. Standard preparation of aniline from nitrobenzene (or Fe/HCl can be used).

Level 2 — Diazonium chemistry (Sandmeyer and others)

Formation: C₆H₅NH₂ + NaNO₂ + HCl (0−5°C) → C₆H₅N₂⁺Cl⁻ (benzenediazonium chloride).

Reactions of diazonium salt:

Sandmeyer reaction: Cu(I) salt (CuCl, CuBr, CuCN) in acidic medium acts as catalyst. Replaces N₂⁺ with Cl, Br, or CN respectively.

Azo coupling (electrophilic aromatic substitution): ArN₂⁺ (electrophile) + C₆H₅OH (slightly alkaline) → p-hydroxyazobenzene (orange). ArN₂⁺ + aniline (slightly acidic) → p-aminoazobenzene. Basis of azo dye synthesis — −N=N− chromophore gives colour.

JEE tip: Sandmeyer → Cu(I) catalyst. Azo coupling → alkaline for phenol, acidic for aniline. Iodide (KI) is added directly, no Cu needed.

NCERT spotlight — Sulpha drugs

Sulphanilic acid (from aniline sulphonation) → precursor of sulpha drugs (first antibiotics). Sulphadiazine, sulphathiazole — inhibit bacterial folic acid synthesis. Historical importance: first chemically synthesised antibacterial agents (1930s). Understanding the role of −NH₂ and −SO₂NH₂ groups in drug design.

Protection of amine in synthesis: Acetylation reduces −NH₂ reactivity → allows selective mono-substitution. After substitution, hydrolyse amide bond (NaOH/H₂O) → free −NH₂ restored. Classic synthetic strategy in making nitroanilines from aniline.

Starting from aniline, how would you synthesise chlorobenzene? (Cannot use direct halogenation of benzene with −NH₂ — too reactive, gives tribromide. Must go via diazonium.)

Step 1 — Convert aniline to diazonium salt:
  C₆H₅NH₂ + NaNO₂ + HCl (0−5°C) → C₆H₅N₂⁺Cl⁻.
Step 2 — Sandmeyer reaction with CuCl/HCl:
  C₆H₅N₂⁺Cl⁻ + CuCl → C₆H₅Cl + N₂ + CuCl.
Step 3 — Product: chlorobenzene ✓.
Why this route? Direct EAS chlorination of aniline → 2,4,6-trichloroaniline (too reactive, polychlorination).
Diazonium route gives monochloro product cleanly.
Note: temperature must stay at 0−5°C for Step 1; warm gently for Step 2.

Applications — synthetic dyes and pharmaceuticals

Azo dyes: over 50% of commercial dyes are azo dyes. Examples: methyl orange (acid-base indicator), Congo red, Bismarck brown. Diazonium chemistry is central to dye industry. Sulpha drugs: sulphanilamide and derivatives — bacteriostatic. Sandmeyer synthesis: practical route to aryl halides and nitriles used in fine chemical and pharmaceutical synthesis.

• Write the Sandmeyer reaction to convert benzene diazonium chloride to benzonitrile.
• How does aniline's −NH₂ group direct incoming electrophiles? Where do they preferentially attack?
• Outline the synthesis of p-hydroxyazobenzene from aniline in two steps.

Open the Practice tab for graded questions on Aromatic Amines.

• Use the platform-native live simulation or PhET-style tool for this topic (number line, Venn, physics playground, molecule builder, sensor dashboard, etc.).
• Mirror / body / home activity: physically do the concept (count objects, measure, role-play) and photograph or describe for portfolio.
• Voice or text reflection with AI Mentor: explain the concept to a younger student or family member.

• "Explain this concept to a Class 6 student using one real example from an Indian home, school, market, or festival."
• "What is one common mistake students make here, and how would you catch yourself making it?"
• Stretch: "How does this connect to coding, robotics, money, health, environment, or a future career?"

• Complete the core practice + one extension activity (photo, table, short reflection, or mini-project) for base XP + topic badge.
• 5-7 day streak or family discussion note = multiplier + visible artifact in parent/principal dashboard.
• Best real-world application stories (anonymised) featured on class or national leaderboard.

• One hands-on project or measurement using the Drishti kit or household items that makes the concept physical.
• Direct link to at least one Future Skill track (Money Management, Green Tech, Cyber Defenders, Micro-Entrepreneurship, AI Mastery, Sustainable Living, Personality Development).
• Coding extension where relevant (simple script, simulation, or data logging).

This material emphasises experiential "learning by doing", competency (apply/create/analyse), vocational exposure, critical thinking, and multidisciplinary connections. Designed to feed live worlds, AI Mentor (with memory), gamification, robotics, parent analytics, and future skills — not just exam prep.

Portfolio Evidence Idea: Your photo/table/reflection/project + one sentence on "How this helps me in real life or a possible future path."

Open the Practice tab for aligned questions (easy/medium/hard + case-based) with full AI scaffolding.

See curriculum for cross-links and the full future-skills/robotics chapters.