Distinction Between 1°, 2°, and 3° Amines

Amines are nitrogen-containing organic compounds that can be classified into Primary (1°), Secondary (2°), and Tertiary (3°) amines based on the number of alkyl or aryl groups attached to the nitrogen atom.

Primary (1°) Amine

Structure: R–NH₂

Definition: One alkyl or aryl group attached to the nitrogen atom.

Examples: Methylamine (CH₃NH₂), Aniline (C₆H₅NH₂)

Secondary (2°) Amine

Structure: R–NH–R′

Definition: Two alkyl or aryl groups attached to the nitrogen atom.

Examples: Dimethylamine ((CH₃)₂NH), Diphenylamine

Tertiary (3°) Amine

Structure: R–N(R′)–R″

Definition: Three alkyl or aryl groups bonded to nitrogen, no hydrogen atom.

Examples: Trimethylamine ((CH₃)₃N), Triphenylamine

Chemical Distinction Tests

1. Hinsberg Test

• 1° Amine: Forms sulfonamide, soluble in alkali.
• 2° Amine: Forms sulfonamide, insoluble in alkali.
• 3° Amine: No reaction.

2. Nitrous Acid Test

• 1° Amine: Brisk evolution of N₂ gas.
• 2° Amine: Forms oily yellow N-nitroso compound.
• 3° Amine: No visible reaction.

3. Acylation Reaction

Primary and secondary amines form amides with acyl chlorides, but tertiary amines do not react.

Summary Table

Property	1° Amine	2° Amine	3° Amine
Structure	R–NH2	R–NH–R′	R–N(R′)–R″
Hinsberg Test	Soluble	Insoluble	No Reaction
Nitrous Acid	Gas Evolution	N-Nitroso	No Reaction
Acylation	Yes	Yes	No
N–H Bonds	2	1	0

Practice Questions

MCQs

1. Which amine reacts with nitrous acid to evolve nitrogen gas?
   a) 1° amine ✅
   b) 2° amine
   c) 3° amine
   d) None
2. Which amine fails in acylation?
   a) 1°
   b) 2°
   c) 3° ✅
   d) All

True / False

1° amines give soluble sulfonamides in Hinsberg test. True ✅

3° amines evolve nitrogen gas with nitrous acid. False ❌

Fill in the Blanks

Primary amines have ___ N–H bonds. Answer: 2

Tertiary amines have ___ N–H bonds. Answer: 0

FAQs

Q1. How do you distinguish between primary, secondary, and tertiary amines?

By Hinsberg test, nitrous acid test, and acylation reactions.

Q2. Which amine does not react with acyl chlorides?

Tertiary (3°) amines do not react due to absence of N–H bond.

🔍 Mastering these distinctions is vital for Class 12 Organic Chemistry, competitive exams like JEE/NEET & advanced research in synthesis.