Libermann nitroso reaction.

Explanation

Both aliphatic and aromatic secondary amines react with nitrous acid, `(NaNO_(2)+HCl)` to form nitrosoamines which are yellow oily liquids and are insoluble in mineral acids.
`underset(2^(@)" amine ")(R_(2)NH+HONO)tounderset("N,N-Dialkylnitrosoamine")(R_(2)N-N=O+H_(2)O)`