Aniline when diazotized in cold and then treated with dimethyl aniline gives a coloured product. Its structure

Question

Aniline when diazotized in cold and then treated with dimethyl aniline gives a coloured product. Its structure would be:

Accepted Answer

The reaction proceeds in two main steps:

1.  **Diazotisation:** Aniline (a primary aromatic amine) reacts with cold nitrous acid (prepared *in situ* from $NaNO_2$ and $HCl$ at 273-278 K) to form **benzenediazonium chloride**.
2.  **Coupling Reaction:** The benzenediazonium cation is a weak electrophile. It undergoes electrophilic aromatic substitution with the highly activated N,N-dimethylaniline ring. Due to steric hindrance caused by the bulky dimethylamino group ($-N(CH_3)_2$), the coupling predominantly occurs at the *para*-position of the N,N-dimethylaniline ring.

The resulting coloured product is a yellow azo dye named **p-(N,N-dimethylamino)azobenzene**. Its chemical structure is $C_6H_5-N=N-C_6H_4-N(CH_3)_2$.

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