Amines — Reactions

• Alkylation and acylation of amines and their products.
• The Hinsberg test for distinguishing primary, secondary, and tertiary amines.
• The carbylamine test as a specific test for primary amines.
• Diazonium salt formation from primary aromatic amines.

Level 1 — Alkylation and acylation

Alkylation (N-alkylation): RNH₂ + R'X → RR'NH (2°) → RR'₂N (3°) → RR'₃N⁺X⁻ (quaternary). Difficult to control; often gives mixture. Gabriel synthesis preferred for 1° amines.

Acylation (reaction with acid chlorides or anhydrides): RNH₂ + R'COCl → RNHCOR' (amide) + HCl. (CH₃CO)₂O (acetic anhydride) + amine → acetamide + CH₃COOH (milder, no HCl). 3° amines cannot be acylated (no N−H to replace).

Products of acylation:

• 1° amine → monosubstituted amide (R−NH−CO−R').
• 2° amine → disubstituted amide (R₂N−CO−R').
• 3° amine → no reaction with acylating agent.

Level 2 — Hinsberg test, Carbylamine, Diazonium

Hinsberg test (distinguishes 1°, 2°, 3°): Reagent: benzenesulphonyl chloride (C₆H₅SO₂Cl) + KOH solution.

• 1° amine → sulphonamide (soluble in excess KOH: has one acidic N−H that is removed by KOH).
• 2° amine → sulphonamide (insoluble in KOH: no N−H to ionise).
• 3° amine → no reaction (no N−H; may form oily layer).

Carbylamine test (isocyanide test) — specific for PRIMARY amines: 1° amine + CHCl₃ + KOH (alc.) → isocyanide (carbylamine) — extremely foul smell. R−NH₂ + CHCl₃ + 3KOH → R−NC (isocyanide) + 3KCl + 3H₂O. 2° and 3° amines: NEGATIVE. Used specifically to identify 1° amines.

Diazonium salt formation (aromatic 1° amines): ArNH₂ + NaNO₂ + HCl (0−5°C) → ArN₂⁺Cl⁻ + NaCl + 2H₂O. Temperature must be kept below 5°C — diazonium salts decompose above this. Aliphatic diazonium salts too unstable (release N₂ immediately).

JEE tip: Carbylamine = primary amine only (smell is the clue — carbylamine = isocyanide, extremely offensive odour). Diazonium formation: 0−5°C is critical — mention temperature in answer.

NCERT spotlight — Gabriel synthesis (pure 1° amine)

Phthalimide + KOH → potassium phthalimide → (RX) → N-alkylphthalimide → (N₂H₄, hydrolysis) → primary amine RNH₂ + phthalhydrazide. Advantage: pure primary amine (no 2° or 3° contamination). Cannot make aromatic 1° amine via Gabriel (aryl halides don't undergo SN2).

Reaction with nitrous acid (HNO₂):

• Aliphatic 1° amine + HNO₂ → unstable aliphatic diazonium → N₂↑ + alcohol (N₂ released immediately — used to detect 1° aliphatic amine).
• Aromatic 1° amine + HNO₂ (0−5°C) → stable diazonium salt (used in synthesis).
• 2° amine + HNO₂ → N-nitroso compound (nitrosamine, yellow oily).
• 3° amine: no reaction with HNO₂ (no N−H).

An unknown amine gives foul smell with CHCl₃/KOH and forms a diazonium salt with NaNO₂/HCl at 0°C. Identify the type and class.

Step 1 — Carbylamine test positive (foul smell with CHCl₃/KOH) → PRIMARY amine confirmed.
Step 2 — Diazonium salt stable at 0°C → AROMATIC primary amine.
Step 3 — (Aliphatic 1° diazonium → immediately loses N₂; does not give stable salt.)
Step 4 — Conclusion: compound is a primary AROMATIC amine, e.g. aniline (C₆H₅NH₂).
Step 5 — Reaction: C₆H₅NH₂ + NaNO₂ + HCl (0−5°C) → C₆H₅N₂⁺Cl⁻ (benzenediazonium chloride) + NaCl + 2H₂O.

Applications — dye and pharmaceutical industry

Diazonium salts are pivotal intermediates — converted to phenols, aryl halides, nitriles (Sandmeyer reactions), azo dyes. Acylation of amines: used to protect amine groups in peptide synthesis. Hinsberg test: classical lab identification of amine class.

• Write the product of acylation of dimethylamine with acetic anhydride.
• How would you distinguish methylamine from dimethylamine using the Hinsberg test?
• Write the carbylamine test equation for ethylamine.

Open the Practice tab for graded questions on Amine Reactions.

• 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.