Question

Complete the following reaction equation: ${{C}_{6}}{{H}_{5}}N{{H}_{2}}+HN{{O}_{2}}\to$ ?

Answer 1

The compound is aromatic and on reaction with nitrous acid a diazonium salt is formed which is very unstable and it dissociates to give desired product.

Complete answer:
In order to answer the question we need to learn about diazonium salts. Aromatic amines go through an electrophilic substitution reaction of aromatic rings. $N{{H}_{2}}$ group present on the ring is the electron and strongly ring activating. It activates the ring by delocalisation of a lone pair of electrons present on the N atom towards the ring. It results in an increase of electron density at ortho and para positions hence $N{{H}_{2}}$ group is -o, -p directing towards electrophilic substitution.
Benzenediazonium chloride is prepared by the reacting aniline with nitrous acid at 273 - 278 K. Nitrous acid is produced in the reaction as the reaction of sodium nitrite with hydrochloric acid proceeds. The conversion of primary aromatic amines into diazonium salt is known as diazotization. Since it is not stable, the diazonium salt is not generally stored and is used immediately as soon as it is prepared.
Now, nitrous acid reacts with the ethylamine and ethyl diazonium salt is formed. However, this is a very unstable salt and then it gets dissociated. The final products that are obtained are nitrogen and ethanol.
The reaction can be represented as:
${{C}_{6}}{{H}_{5}}N{{H}_{2}}+HN{{O}_{2}}\to {{C}_{2}}{{H}_{5}}OH+{{N}_{2}}$.

Note: Diazonium salts are very good intermediates for the introduction of halogens in the aromatic system. Thus, replacing the diazo group by other groups can be helpful in preparing those substituted aromatic compounds which are generally not prepared by direct substitution in benzene.