Amines in Organic Chemistry: Types, Properties, and Reactions

Amines are one of the most important classes of compounds in organic chemistry. They are derivatives of ammonia (NH₃) where one or more hydrogen atoms are replaced by alkyl or aryl groups. Amines play a vital role in pharmaceuticals, dyes, agrochemicals, and many biological processes.

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1. Classification of Amines

Amines are classified based on the number of alkyl or aryl groups attached to the nitrogen atom:

Type	Structure	Example
Primary (1°)	R–NH₂	Methylamine (CH₃NH₂)
Secondary (2°)	R₂–NH	Dimethylamine ((CH₃)₂NH)
Tertiary (3°)	R₃–N	Trimethylamine ((CH₃)₃N)
Quaternary Ammonium Salt	R₄–N⁺	Tetramethylammonium chloride

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2. Nomenclature of Amines

Amines can be named by two methods:

1. Common name: Alkyl groups attached to nitrogen followed by “amine.”
   • Example: CH₃NH₂ → Methylamine
2. IUPAC name: Replace “-e” of parent hydrocarbon with “-amine.”
   • Example: CH₃CH₂NH₂ → Ethanamine

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3. Physical Properties of Amines

• State: Lower amines (like methylamine) are gases; others are liquids or solids.
• Solubility: Primary and secondary amines are soluble in water due to hydrogen bonding. Tertiary amines are less soluble.
• Boiling Point: Amines have higher boiling points than alkanes but lower than alcohols of similar molecular mass.
• Odour: Many amines have a characteristic fishy smell.

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4. Chemical Properties of Amines4.1 Basicity

• Amines are basic due to the lone pair on nitrogen.
• Order of basicity (in aqueous solution): Secondary > Primary > Tertiary (for aliphatic amines).

4.2 Reactions

1. Acid–Base Reaction: Amines react with acids to form ammonium salts.
   • Example: CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻
2. Acylation: Reaction with acyl chlorides to form amides.
   • Example: CH₃NH₂ + CH₃COCl → CH₃NHCOCH₃ + HCl
3. Alkylation: Amines react with alkyl halides to form higher amines.
4. Diazotization: Primary aromatic amines react with nitrous acid to form diazonium salts.

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5. Uses of Amines

• Pharmaceuticals: Example – Ephedrine, Morphine.
• Dyes: Example – Aniline in dye industry.
• Agrochemicals: Example – Fungicides and insecticides.
• Biological importance: Amines like amino acids, neurotransmitters (dopamine, serotonin).

Below is a COMPLETE, EXAM-ORIENTED list of IMPORTANT NAMED REACTIONS OF AMINES (Class 12 Chemistry) with CLEAR MECHANISMS, written in stepwise language suitable for CBSE Boards + JEE Main/Advanced.
You can directly copy-paste this into notes, PDFs, or teaching material.

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📘 CLASS 12 CHEMISTRY

AMINES – NAMED REACTIONS WITH MECHANISM

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1️⃣ HOFFMANN BROMAMIDE REACTION

(Very Important – Carbon Chain Shortening)

Reaction:

When an amide is treated with bromine and alkali, a primary amine with one carbon less is formed.

General Equation:

R–CONH₂ + Br₂ + 4KOH → R–NH₂ + K₂CO₃ + 2KBr + 2H₂O

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🔬 Mechanism (Stepwise):

Step 1: Formation of N-Bromoamide
R–CONH₂ + Br₂ + OH⁻ → R–CONHBr

Step 2: Deprotonation
R–CONHBr + OH⁻ → R–CONBr⁻

Step 3: Rearrangement (Key Step)
Alkyl group migrates from carbonyl carbon to nitrogen.

R–CONBr⁻ → R–N=C=O (Isocyanate)

Step 4: Hydrolysis
R–N=C=O + H₂O → R–NH₂ + CO₂

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🔑 Key Points:

✔ Only primary amines formed
✔ One carbon atom lost
✔ Migration step is crucial

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2️⃣ GABRIEL PHTHALIMIDE SYNTHESIS

(Preparation of Pure Primary Aliphatic Amines)

Reaction:

Phthalimide is converted into potassium salt, which reacts with alkyl halide.

General Equation:

Phthalimide + KOH → Potassium phthalimide
Potassium phthalimide + R–X → N-alkyl phthalimide
Hydrolysis → R–NH₂

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🔬 Mechanism:

Step 1: Formation of Potassium Phthalimide
Phthalimide + KOH → C₆H₄(CO)₂N⁻K⁺

Step 2: Nucleophilic Substitution (SN2)
C₆H₄(CO)₂N⁻ + R–X → N-alkyl phthalimide

Step 3: Hydrolysis
N-alkyl phthalimide + H₂O → R–NH₂

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🔑 Key Points:

✔ Gives only 1° amines
✔ Not suitable for aryl halides
✔ Avoids formation of secondary & tertiary amines

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3️⃣ CARBYLAMINE REACTION

(Isocyanide Test – Qualitative Test)

Reaction:

Primary amines when heated with chloroform and alcoholic KOH form isocyanides (foul smell).

General Equation:

R–NH₂ + CHCl₃ + 3KOH → R–NC + 3KCl + 3H₂O

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🔬 Mechanism:

Step 1: Formation of Dichlorocarbene
CHCl₃ + OH⁻ → :CCl₂

Step 2: Attack by Primary Amine
R–NH₂ + :CCl₂ → Intermediate

Step 3: Rearrangement
Intermediate → R–NC (Isocyanide)

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🔑 Key Points:

✔ Given by only 1° amines
✔ Used to distinguish 1°, 2°, 3° amines
✔ Strongly smelling product

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4️⃣ DIAZOTIZATION REACTION

(Aromatic Amines – Most Important)

Reaction:

Primary aromatic amines react with nitrous acid (HNO₂) at 0–5°C to form diazonium salts.

Example:

C₆H₅NH₂ + NaNO₂ + HCl → C₆H₅N₂⁺Cl⁻ + 2H₂O

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🔬 Mechanism:

Step 1: Formation of Nitrous Acid
NaNO₂ + HCl → HNO₂

Step 2: Formation of Nitrosonium Ion
HNO₂ + H⁺ → NO⁺ + H₂O

Step 3: Attack on Aniline
C₆H₅NH₂ + NO⁺ → Intermediate

Step 4: Loss of Water
Intermediate → C₆H₅N₂⁺Cl⁻

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🔑 Key Points:

✔ Temperature must be 0–5°C
✔ Forms benzene diazonium chloride
✔ Used to prepare phenols, halides, cyanides

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5️⃣ HINSBERG TEST

(Distinguishing Test)

Reagent:

Benzenesulphonyl chloride (C₆H₅SO₂Cl)

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Reactions:

Primary amine:
Forms soluble sulphonamide in alkali.

Secondary amine:
Forms insoluble sulphonamide.

Tertiary amine:
No reaction.

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🔑 Key Points:

✔ Distinguishes 1°, 2°, 3° amines
✔ Based on solubility behavior

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6️⃣ ACYLATION REACTION

(Schotten–Baumann Reaction)

Reaction:

Amines react with acid chlorides or anhydrides.

R–NH₂ + R′COCl → R–NHCO–R′ + HCl

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🔬 Mechanism:

• Lone pair on nitrogen attacks carbonyl carbon

• Chloride ion leaves

• Amide formed

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🔑 Key Points:

✔ 1° and 2° amines react
✔ 3° amines do not
✔ Used for identification

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7️⃣ REDUCTION OF NITRO COMPOUNDS

(Preparation of Amines)

Reaction:

Nitro compounds are reduced to amines.

C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O

Reagents:

• Sn/HCl

• Fe/HCl

• H₂/Pd

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🔬 Mechanism:

NO₂ → NHOH → NH₂

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🔑 FINAL EXAM SUMMARY (VERY IMPORTANT)

• Hoffmann reaction → chain shortening

• Gabriel synthesis → pure 1° amine

• Carbylamine → test for 1° amines

• Diazotization → aromatic amines

• Hinsberg → distinction test

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