Revision: Organic Compounds Containing Nitrogen >> Amines Chemistry HSC Science (General) 12th Standard Board Exam Maharashtra State Board

Primary amines (1°) are the ammonia derivatives in which one H-atom has been replaced by one alkyl or aryl group.

Secondary amines (2°) are the ammonia derivatives in which two hydrogen atoms have been replaced by two alkyl or aryl groups.

Tertiary amines (3°) are the ammonia derivatives in which three hydrogen atoms have been replaced by three alkyl or aryl group.

• Amines overview: Amines are derivatives of ammonia (NH₃) where one or more H-atoms are replaced by alkyl/aryl groups; they can be saturated or unsaturated.
• Classification by source: Aliphatic amines (e.g., CH₃–NH₂, methylamine) and Aromatic amines (e.g., C₆H₅–NH₂, aniline).
• Classification by H-substitution: Primary (1°, –NH₂, e.g., methylamine), Secondary (2°, –NH–, e.g., dimethylamine), and Tertiary (3°, –N–, e.g., trimethylamine).
• Sub-types of 2° and 3° amines: Simple/symmetrical (same groups, e.g., (C₂H₅)₂NH, (C₂H₅)₃N) and Mixed/unsymmetrical (different groups, e.g., C₂H₅–NH–CH₃, C₂H₅–N(CH₃)₂).
• Examples of each class: 1° – n-butylamine, sec-butylamine, tert-butylamine, aniline; 2° – dimethylamine, diethylamine, diphenylamine; 3° – trimethylamine, triethylamine, triphenylamine.

• Preparation: Amines are obtained by reduction of alkyl nitriles (LiAlH₄ / Na-ethanol – Mendius), nitroalkanes (LiAlH₄ or Sn/HCl), and amides (LiAlH₄).
• Hoffmann's ammonolysis: RX + excess alc. NH₃ → mixture of 1°, 2°, 3° amines & quaternary salt; reactivity RI > RBr > RCl.
• Gabriel phthalimide synthesis: Phthalimide + KOH → R–X → hydrolysis gives pure 1° amine (RNH₂).
• Hoffmann bromamide degradation: RCONH₂ + Br₂ + 4KOH → RNH₂ (amine with one less C).
• Reactions of ethanamine: exhaustive alkylation → (C₂H₅)₄N⁺Br⁻; CH₃COCl → N-ethylethanamide; CHCl₃/KOH → ethyl isocyanide (carbylamine test); HNO₂ → ethanol; C₆H₅SO₂Cl → Hinsberg's test product.