Question

Nitronium ion ${\text{NO}}_2^ + $ is generated by the:
A. Protonation of nitric acid.
B. Deprotonation of nitric acid.
C. Both A and B
D. None of these

Answer 1

Hint: 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.

Step by step answer: The formula of nitric acid is ${\text{HN}}{{\text{O}}_{\text{3}}}$
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 so option (A) is correct.
The deprotonation of nitric acid gives the nitrate ion, not nitronium ion.
On dissolving the nitric acid in the water, nitric acid dissociates into proton and nitrate ions.
The formation of nitrate ion is shown as follows:
${\text{HN}}{{\text{O}}_{\text{3}}}\,{\text{ + }}\,\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to \,{{\text{H}}^ + }\, + \,{\text{NO}}_3^ - \,$
So, deprotonation of nitric acid does not give nitronium ion so, option (B) is incorrect.

Therefore, option (A) Protonation of nitric acid, is correct.

Additional information: Nitric acid is a strong oxidizing agent. The protonation of nitric acid gives nitronium ion so the nitric acid is used for the nitration. The process of the addition of nitronium ions into the substrate by removing other ions is known as nitration. Nitration is a substitution type reaction.

Note: Nitrate ion is the conjugate base of nitric acid produced by deprotonation. Nitronium ion is stable in normal conditions. Nitronium ion is an electrophile used for nitration.