Test for Amines

NaNO₂ + aq. HCl Test:

• 1° Aliphatic amine: 
  \[ \mathrm{R} - \mathrm{CH}_2\mathrm{NH}_2 \xrightarrow{\mathrm{NaNO}_2 + \text{aq, HCl}} \mathrm{R} - \mathrm{CH}_2 - \mathrm{OH} + \mathrm{N}_2 \uparrow \]

• 1° Aromatic amine: 
  \[ \mathrm{Ph} - \mathrm{NH}_2 \xrightarrow[(0-5^\circ\mathrm{C})]{\mathrm{NaNO}_2 + \text{aq. HCl}} \mathrm{Ph} - \overset{+}{\mathrm{N}}_2\overset{\ominus}{\mathrm{Cl}} \text{ (diazonium salt)} \]

• All secondary amine give yellow oily liquid with nitrous acid i.e. NaNO₂ + HCI

  \[ 2^\circ \text{ Amine \%: } \mathrm{R} - \mathrm{NH} - \mathrm{R} \xrightarrow{\mathrm{NaNO}_2 + \text{aq. HCl}} \mathrm{R}_2\mathrm{N} - \mathrm{NO} \]

  yellow oily liquid (N-Nitroso amine)

  \[ 3^\circ \text{ Amine: } \mathrm{R}_3\mathrm{N} \xrightarrow{\mathrm{NaNO}_2 + \text{aq. HCl}} \text{unstable nitrite} \]

Carbylamine Test (Isocyanide Test):

• Only 1° amines give this test

• \[ \mathbf{1^\circ \text{ Amine : }} \mathrm{R} - \mathrm{CH}_2 - \mathrm{NH}_2 \xrightarrow{\mathrm{CHCl}_3 + \mathrm{KOH}} \mathrm{R} - \mathrm{CH}_2 - \mathrm{N} \equiv \mathrm{C} + 3\mathrm{KCl} + 3\mathrm{H}_2\mathrm{O} \text{ (unpleasant smell of isocyanide)} \]

• \[ \mathrm{Ph} - \mathrm{NH}_2 \xrightarrow{\mathrm{CHCl}_3 + \mathrm{KOH}} \mathrm{Ph} - \mathrm{N} \equiv \mathrm{C} \]

• 2° and 3° amines do NOT give this test

Hofmann Mustard Oil Test (CS₂ test):

Test for 1° amine and aniline

2° amine reacts with CS₂

3° amine + CS₂ → no reaction

Hinsberg Reagent (Benzenesulphonyl chloride, C₆H₅SO₂Cl):

• 1° amine: 
  \[ \mathrm{R} - \mathrm{NH}_2 + \mathrm{PhSO}_2\mathrm{Cl} \xrightarrow{\text{Pyridine}} \mathrm{R} - \mathrm{NH} - \mathrm{SO}_2 - \mathrm{Ph} \xrightarrow{\text{Base}} \text{Compound is soluble in base.} \]

• 2° amine: 
  \[ \mathrm{R}_2\mathrm{NH} + \mathrm{PhSO}_2\mathrm{Cl} \xrightarrow{\text{Pyridine}} \mathrm{R}_2\mathrm{N} - \mathrm{SO}_2 - \mathrm{Ph} \xrightarrow{\text{Base}} \text{Compound is insoluble in base.} \]

• 3° amine: 
  \[ \mathrm{R}_3\mathrm{N} + \mathrm{PhSO}_2\mathrm{Cl} \xrightarrow{\text{Pyridine}} \text{No reaction.} \]

Azo-dye test:

1° aromatic amines + NaNO₂ + HCl → diazonium salt → couple with alkaline β-naphthol → orange-red dye