CBSE/NEET/JEE Chemistry: Amines

Classification & Nomenclature

Amines are derivatives of ammonia where H is replaced by alkyl/aryl groups.
Classes: 1° (one C–N bond), 2° (two), 3° (three).
IUPAC suffix: –amine.

Methods of Preparation

From alkyl halides + NH₃: gives mixture of 1°, 2°, 3° amines and quaternary salts.
Reduction: nitro compounds, nitriles, amides → amines (LiAlH₄ or H₂/Ni, Pt, Pd).
Hofmann bromamide degradation: amide → 1° amine with one carbon less (Br₂/KOH).
Gabriel phthalimide synthesis: pure 1° aliphatic amines only (not aromatic).

Basicity of Amines (High-Frequency)

All aliphatic amines > NH₃; aromatic amines (aniline) < NH₃.
Aqueous phase: methyl series 2° > 3° > 1°; ethyl series 2° > 1° > 3°.
Non-aqueous (e.g., chlorobenzene): 3° > 2° > 1° (inductive effect dominates).
Ortho effect: o-substituted anilines are weaker bases than aniline irrespective of substituent nature.

Memory hook: Water crowding favors the middle (2°); non-water favors the maximum donors (3°).

Identification Tests & Name Reactions

Hinsberg test: 1° → soluble in KOH; 2° → insoluble; 3° → no reaction.
Carbylamine: only 1° amines → foul-smelling isocyanides.
HNO₂: aliphatic 1° → alcohol + N₂; aromatic 1° → diazonium salts (273–278 K).
Liebermann nitroso: 2° amines → yellow oily N-nitrosoamines → green → blue on alkalisation.
Azo coupling: diazonium salts + phenols/anilines → colored azo dyes.

Common Mistakes

Using Gabriel synthesis for aromatic amines.
Forgetting phase while ordering basicity.
Applying carbylamine test to 2°/3° amines.

Compact Recap

Prep routes: reduction, Hofmann (–1 C), Gabriel (1° aliphatic).
Tests: Hinsberg (class), Carbylamine (1°), Nitroso (2°).
Basicity depends on solvent; ortho effect weakens aniline.