This lesson explains the structure, properties, reactions, and importance of nitrogen-containing organic compounds—primarily amines and diazonium salts.

1. Core Concepts (Short Notes)

14.1 Amines (R–NH₂, R₂NH, R₃N)

Amines are organic derivatives of ammonia (NH₃).

• Primary amine (1°): R–NH₂

• Secondary amine (2°): R₂NH

• Tertiary amine (3°): R₃N

14.2 Basicity of Amines

Amines act as weak bases because the nitrogen atom carries a lone pair of electrons.

• Can accept H⁺ to form substituted ammonium ions.

• Basic strength: aromatic amines < aliphatic amines (due to electron-withdrawing ring).

14.3 Physical Properties of Amines

• Lower amines: fishy smell, volatile.

• Hydrogen bonding in primary & secondary amines → higher boiling points.

• Soluble in water (small amines).

2. Reactions of Amines

14.4 Reaction With Acids

14.5 Reaction With Nitrous Acid

Depends on type of amine:

• 1° aliphatic amines: form alcohols.

• 2° amines: form nitrosamines.

• 3° amines: form soluble salts.

• 1° aromatic amines (e.g., aniline): form diazonium salts.

3. Diazonium Salts (Ar–N₂⁺X⁻)

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4.6 Formation of Diazonium Salts

Aromatic amines react with nitrous acid at 0–5°C: ArNH₂ + HNO₂ + HCl → Ar–N₂⁺Cl⁻ + 2H₂O

14.7 Stability

• Aromatic diazonium salts: stable at low temperature.

• Aliphatic diazonium salts: very unstable.

14.8 Reactions of Diazonium Salts

Used for synthesis of dyes, phenols, and halobenzenes.

(a) Sandmeyer Reactions

Form aryl halides: Ar–N₂⁺ + CuCl/HCl → Ar–Cl Ar–N₂⁺ + CuBr/HBr → Ar–Br

(b) Formation of Phenols

Ar–N₂⁺ + H₂O → Ar–OH + N₂↑

(c) Azo Coupling (Dye Formation)

Diazonium salts react with phenols or aromatic amines to form colored azo dyes. 

Example: Ar–N₂⁺ + Ar′–NH₂ → Ar–N=N–Ar′

2. Key Patterns & Reactions to Memorize

Base Strength Order

Diazonium Salt Uses

• Dye industry

• Preparation of phenols

• Synthesis of halogenated aromatics

Azo Coupling Color

Azo dyes are intensely colored due to extended conjugation.

3. Tips & Tricks for Exams

• Maintain low temperature (0–5°C) during diazotization.

• Know the difference between aliphatic and aromatic amine behavior.

• Remember: 1° aromatic amines → diazonium salts.

• Azo dyes are always bright (yellow, orange, red).

• For naming amines, locate the longest carbon chain and label substituents.

• Watch out for basicity questions—electron donors increase basicity; electron withdrawers decrease it.

4. Important Points to Remember

• Amines behave as weak bases due to the lone pair on nitrogen.

• Diazotization is a key reaction for aromatic amines.

• Diazonium salts are versatile intermediates for synthesizing many aromatic compounds.

• Azo coupling produces colored dyes widely used in industry.

Temperature control is crucial in diazonium salt formation.