Amines: Preparations and Reactions (JEE Advanced)

“Preparation from nitro compounds, nitriles and amides; Reactions: Hoffmann bromamide degradation, Gabriel phthalimide synthesis; Reaction with nitrous acid, Azo coupling reaction of diazonium salts of aromatic amines; Sandmeyer and related reactions of diazonium salts; Carbylamine reaction, Hinsberg test, Alkylation and acylation reactions”

Source: JEE Advanced 2026 Information Bulletin, Annexure-I. Closest JEE Main topic: Nomenclature, classification, structure, basic character and identification of primary, secondary and tertiary amines.

JEE Main focuses only on basic properties and identification of amines, while Advanced demands you know specific synthetic routes and reaction mechanisms like Hoffmann degradation and Sandmeyer reactions. These named reactions and diazonium salt transformations are tested heavily in Advanced but are completely absent from Main.

• Reduction of nitro compounds (using Sn/HCl, Fe/HCl, or catalytic hydrogenation) gives primary amines; nitrile reduction with LiAlH₄ or H₂/Ni gives primary amines with one extra carbon
• Hoffmann bromamide degradation converts RCONH₂ to RNH₂ using Br₂/NaOH, losing one carbon from the chain
• Gabriel synthesis uses potassium phthalimide to make pure primary amines without secondary or tertiary amine contamination
• Primary aromatic amines react with NaNO₂/HCl at 0-5°C to form diazonium salts; aliphatic primary amines give unstable diazonium salts that decompose to alcohols with N₂ evolution
• Sandmeyer reaction replaces N₂⁺ with Cl, Br, or CN using Cu₂X₂ catalyst; related reactions include Gattermann (Cu powder for Cl/Br) and Balz-Schiemann (for F using HBF₄)
• Carbylamine test is specific for primary amines: R-NH₂ + CHCl₃ + 3KOH → R-NC (foul smell); Hinsberg test distinguishes 1°, 2°, and 3° amines using benzenesulfonyl chloride

• R-NO₂ + 3H₂ (Ni catalyst) → R-NH₂ + 2H₂O
• R-CN + 4[H] (LiAlH₄) → R-CH₂-NH₂
• RCONH₂ + Br₂ + 4NaOH → RNH₂ + Na₂CO₃ + 2NaBr + 2H₂O (Hoffmann)
• C₆H₅NH₂ + NaNO₂ + 2HCl (0-5°C) → C₆H₅N₂⁺Cl⁻ + NaCl + 2H₂O
• C₆H₅N₂⁺Cl⁻ + CuCl → C₆H₅Cl + N₂ (Sandmeyer)
• C₆H₅N₂⁺Cl⁻ + C₆H₅OH (alkaline) → C₆H₅-N=N-C₆H₄OH (azo dye)
• R-NH₂ + CHCl₃ + 3KOH → R-NC + 3KCl + 3H₂O (Carbylamine)
• 1° amine + C₆H₅SO₂Cl + NaOH → soluble sulfonamide salt (Hinsberg)

• Forgetting that Hoffmann degradation reduces the carbon chain by one (product has one less carbon than the amide)
• Confusing reaction conditions: diazonium salt formation requires 0-5°C for aromatic amines, while aliphatic amines give alcohols even at low temperature because their diazonium salts are too unstable
• Mixing up Sandmeyer (uses Cu₂X₂ or CuX) with Gattermann (uses Cu powder) and forgetting that iodine replacement needs KI without any copper catalyst
• In Hinsberg test, forgetting that 2° amines give insoluble sulfonamide (no acidic H to form salt), while 3° amines do not react at all

Question. An aromatic compound A (C₇H₉N) does not respond to Hinsberg test but gives a positive carbylamine test. A on treatment with NaNO₂/HCl at 0-5°C followed by reaction with phenol in alkaline medium gives an orange dye B. Identify A and B.

Solved twice independently; both solutions agree.