(b) Nitrosation of aromatic amines
When aromatic amines undergo process of nitrosation by nitrosyl cation, electrophilic aromatic substitution occurs and then nitroso derivatives are formed. For example:

Only very strong activating group, for example aniline and its derivatives can react with very weak electrophile nitrosyl with nitrosyl cation it resemble with secondary amines where synthesis of N-alkyl nitrosoproduct takes place.

Alkyl diazomium ions are not stable due to positively charged nitrogen atom but aryl diazonium ions are much more stable due to resonance and can be stored aqueous solution at 0°C to 5°C for long periods of time and loss of nitrogen form an unstable aryl cation and is much slower than loss of nitrogen from an alkyl diazonium ion so C₆H₅N⁺ ₂
immediately reacts with chloride ion to form benzene diazonium chloride.

Here NaNO₂and HCl are taken in 1 : 3 so excess chloride ion quickly reacts with intermediate otherwise electrophile C₆H₅N⁺ ₂
immediately reacts with nucleophilic aniline to form coupling azo product.

Aryl diazonium ions undergo a variety of reactions which makes them versatile intermediates for the preparation of many ring substituted aromatic derivatives for example

These reactions occur only when amino group attached directly with benzene ring but when benzyl derivatives type compounds undergo these reactions they form normal aliphatic amines type products.

When methyl amines reacts with nitrous acid they form alkoxyalkanes as major product.

(x) Separation of 1^o, 2^o and 3^o Amines