Chemical Reactions of Amines

Acid-Base Reactions

1. Basic Character of Amines

Amines act as bases due to the lone pair of electrons on nitrogen, which can accept a proton (H⁺), forming an ammonium ion.

Example:
CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻

Substitution Reaction

2. Alkylation of Amines

Amines react with alkyl halides to form substituted amines and quaternary ammonium salts if excess alkyl halide is used.

Example:
CH₃NH₂ + CH₃Cl → (CH₃)₂NH + HCl

Acylation

3. Acylation with Acid Chlorides

Primary and secondary amines react with acid chlorides or anhydrides to form substituted amides — known as acylation.

Example:
R-NH₂ + CH₃COCl → R-NHCOCH₃ + HCl

Nitrosation

4. Reaction with Nitrous Acid

Primary aliphatic amines react with HNO₂ to give alcohols and nitrogen gas, while aromatic amines form diazonium salts, important in dye synthesis.

Example (Aliphatic): R-NH₂ + HNO₂ → R-OH + N₂ + H₂O
Example (Aromatic): Aniline + HNO₂ → Diazonium salt

Test Reaction

5. Carbylamine Reaction

Primary amines react with chloroform and alcoholic KOH to give foul-smelling isocyanides — used as a test for primary amines.

Example:
R-NH₂ + CHCl₃ + 3KOH → R-NC + 3KCl + 3H₂O

Amines show rich reactivity due to their lone pair on nitrogen — making them essential in both laboratory synthesis and biological systems.

Practice Quiz on Amines

MCQs

1. Amines act as bases due to:
   • A) Presence of hydrogen atoms
   • B) Lone pair of electrons on nitrogen ✅
   • C) Presence of double bonds
   • D) Their high electronegativity
2. The carbylamine test is used to detect:
   • A) Secondary amines
   • B) Tertiary amines
   • C) Primary amines ✅
   • D) Aromatic hydrocarbons

Fill in the Blanks

1. Primary aliphatic amines with nitrous acid give __________ and nitrogen gas. (Answer: Alcohols)

2. Amines + alkyl halides → __________ ammonium salts. (Answer: Quaternary)

True / False

1. Amines cannot undergo acylation reactions. ❌ (False)

2. Aniline reacts with nitrous acid to form diazonium salts. ✅ (True)