Question

In the nitration of benzene with a mixture of concentrated ${\text{HN}}{{\text{O}}_3}$ with concentrated ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ the active species involved
in:
A. ${\text{NO}}_3^ -$
B. ${\text{N}}{{\text{O}}_2}$
C. ${\text{NO}}_2^ -$
D. ${\text{NO}}_2^ +$

Answer 1

The active species formed by the reaction of nitric acid and sulphuric acid is an electrophile. The electrophile formed by this reaction is used in nitration.

Step by step answer: Nitric acid is a strong oxidizing agent. The protonation of nitric acid gives nitronium ion so the nitric acid is used for the nitration of benzene. The reaction of the addition of nitronium ion into the benzene by removing hydrogen is known as nitration. Nitration is an electrophilic substitution type reaction.
The nitric acid can be protonated by taking a stronger acid than nitric acid.
Sulphuric acid is stronger than nitric acid.
When sulphuric acid reacts with nitric acid. Sulphuric acid gives proton to nitric acid and nitric acid gets protonated. Then a water molecule eliminates from the protonated nitric acid and nitronium ion forms.
The reaction of nitric acid with sulphuric acid is as follows:
${\text{HN}}{{\text{O}}_{\text{3}}}\,{\text{ + }}\,\,{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}\, \to \,{\text{HSO}}_4^ - \, + \,{\text{NO}}_2^ + \, + \,{{\text{H}}_{\text{2}}}{\text{O}}$
So, the nitronium ion can be generated by the protonation of nitric acid
Nitronium ion is generated by the removal of water from nitric acid. Water can be removed from nitric acid by the addition of a proton to nitric acid.
The formula of nitronium ion is ${\text{NO}}_2^ +$.

Therefore, option (D) ${\text{NO}}_2^ +$, is correct.

Note: Nitronium ion is stable in normal conditions. Nitronium ion is an electrophile used for nitration. ${\text{NO}}_3^ -$ is nitrate ion formed by deprotonation of nitric acid. ${\text{N}}{{\text{O}}_2}$is also electrophile. ${\text{NO}}_3^ -$ and ${\text{NO}}_2^ -$ are nucleophile.