Diazotisation
A primary aromatic amine reacts with nitrous acid (NaNO2 and HCl) at 273 to 278 K to give a diazonium salt.
AnilineC₆H₅NH₂Amine - Step 1
NaNO₂ + HCl
273 to 278 K
Benzene diazonium chlorideC₆H₅N₂⁺Cl⁻Diazonium salt
How it works
- NaNO₂ and HCl generate nitrous acid in situ.
- The nitrosating species attacks the amine nitrogen.
- Loss of water gives the diazonium chloride.
What it makes
Benzene diazonium chloride, the starting point for the Sandmeyer, Gattermann, Balz-Schiemann and coupling reactions.
Where it fails
Keep it cold; above 278 K the salt decomposes. Aliphatic amines give unstable diazonium salts that form alcohols at once.
Class 12, Chapter 9 Amines
Diazotisation: quick answers
Why is nitrous acid prepared in situ?
It is unstable, so it is generated from NaNO2 and HCl in the reaction mixture.
What happens to an aliphatic amine?
It forms an unstable diazonium salt that gives the alcohol and N2.
What temperature is required?
273 to 278 K.