Distinguishing between primary, secondary and tertiary amines

Distinguishing between primary, secondary and tertiary amines

Reagent: nitrous acid (NaNO₂, HCl (0-5⁰C))

Observation

(i) Primary amine: effervescence

Equation

RNH₂ + NaNO₂ + 2HCl     →           RCl  +  N₂(g) +H₂O + NaCl

(ii) Secondary amines: yellow oil liquid

Equation

R₂NH  + NaNO₂  +  HCl    →           R₂N-NO  + NaCl  +  H₂O

(iii) Tertiary amines: no observable change du to the formation of soluble diazonium salts

Equation

R₃N  +  NaNO₂  +  4HCl    →           RN₂Cl  +  2RCl   +  NaCl  +  2H₂O

(iv) Aromatic amine: no observable change due to the formation of soluble diazonium salts

Equation

ArNH₂  +  NaNO₂  + 2HCl →          ArN₂Cl  +   NaCl  +  2H₂O

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