Amines
Class 12 · Updated 2026-10-03. Published for practice.
Structure and basicity
Amines are weak bases (lone pair on N accepts H+). Aliphatic amines are more basic than ammonia; aromatic amines (aniline) are less basic because lone pair delocalises into the ring.
Order in gas phase vs aqueous can differ (solvation). Aniline is acetylated before nitration to protect –NH2 from oxidising acid conditions.
Preparation
Reduction of nitro compounds (Sn/HCl or catalytic H2), reduction of nitriles, amination of alkyl halides (mixture of 1°, 2°, 3° — Gabriel phthalimide gives primary amines cleanly).
From amides: Hoffmann bromamide degradation (one carbon shorter primary amine).
Diazonium salts
Ar–NH2 → diazonium ion in cold (0–5 °C) NaNO2 + HCl. Aliphatic diazonium ions are unstable.
Sandmeyer (CuCl, CuBr, CuCN) replaces N2 with halogen or CN. Azo coupling with phenol/aniline gives azo dyes (coloured products — qualitative link).