Amines — Part 2: Reactions of amines and diazonium salts: visual lesson, CBSE Class 12 Chemistry

Lesson

Reactions of amines

Part 2 — amines as bases and nucleophiles, aniline’s activated ring, and the versatile diazonium salts.

In this lesson you will

Write acylation, carbylamine and nitrous acid reactions of amines
Use the Hinsberg test to distinguish 1°, 2° and 3° amines
Explain electrophilic substitution in aniline and why the amino group is protected
Prepare benzenediazonium chloride and write its replacement and coupling reactions and uses in synthesis

Concept

Salts, alkylation and acylation

Amines form salts with acids (soluble in water; the amine is released by NaOH). They are alkylated by alkyl halides (up to quaternary salts). Primary and secondary amines are acylated by acid chlorides or anhydrides (pyridine removes HCl), giving amides; tertiary amines have no N–H and are not acylated.

\ce{C2H5NH2 + CH3COCl -> C2H5NHCOCH3 + HCl}

\ce{C6H5NH2 + (CH3CO)2O -> C6H5NHCOCH3 + CH3COOH}

Table of reactions of primary, secondary and tertiary amines with acid, ethanoyl chloride and excess iodomethane
Reagent	1° amine	2° amine	3° amine
Acid (HCl)	Salt	Salt	Salt
CH₃COCl	N-substituted amide	N,N-disubstituted amide	No acylation
Excess CH₃I	Quaternary salt	Quaternary salt	Quaternary salt

Concept

Carbylamine and nitrous acid reactions

Carbylamine test: only primary amines (aliphatic and aromatic), warmed with CHCl₃ and ethanolic KOH, give isocyanides with a foul smell. Nitrous acid (NaNO₂ + HCl): 1° aliphatic amines → alcohols + N₂ (unstable diazonium); 1° aromatic amines at 273–278 K → diazonium salts.

\ce{C6H5NH2 + CHCl3 + 3KOH -> C6H5NC + 3KCl + 3H2O}

\ce{RNH2 + HNO2 -> ROH + N2 + H2O}

Table of the nitrous acid and carbylamine reactions of different classes of amine
Amine	With HNO₂ (NaNO₂ + HCl)	Carbylamine test
1° aliphatic	N₂ evolved, alcohol formed	Positive
1° aromatic (cold)	Diazonium salt	Positive
2° and 3°	No N₂ (other products)	Negative

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