3.0 Nitration

Nitration reaction is generally carried out with a mixture of concentrated nitric acid and sulphuric acid. The reagents which cause nitration are called nitrating agents.

The various nitrating agents which are commonly employed are:

1. ${N_2}{O_5}$ in $CC{l_4}$ in the presence of ${P_2}{O_5}$ is used when anhydrous conditions are required.

2. Ethyl nitrate $\left( {{C_2}{H_5}ON{O_2}} \right)$ is used to carry out nitration in alkaline medium.

3. In the case of polycyclic hydrocarbons ${N_2}{O_4}$ and nitronium salts such as , $NO_2^ + $ $BF_4^ - $ $NO_2^ + $ $PF_6^ - $ $N{O_2}^ + S{O_3}^-$ can be used.

The electrophile involved in nitration reaction is nitronium ion $\left( {NO_2^ \oplus } \right)$.

1. Generation of electrophile from nitrating agent:

(a) In a mixture of nitric acid and sulphuric acid, an acid base reaction takes place in which nitric acid acts as the base.

(b) ${N_2}{O_5}$ in $CC{l_4}$ when used, results in a spontaneous dissociation reaction.

(c) With concentrated $HN{O_3}$ alone

The electrophile generated in this case is obtained by the behaviour of one nitric acid as the base and other molecule as the acid, but the equilibrium lies in the reactant side