Question

What is the equilibrium of concentrated nitric acid + sulfuric acid to form nitrobenzene obtained by nitrating benzene?

Answer 1

Sulfuric and nitric acids form a nitrating mixture by protonation, and formation of the `NO_2^+` electrophile.

Explanation:

Sulfuric acid is a strong enuff acid to dehydrate nitric acid:

`HO-S(=O)_2OH + HO-N^(+)(=O)O^(-)`

`rightleftharpoonsHSO_4^(-) + H_2""^(+)O-N^(+)(=O)O^(-)`

`rightleftharpoons H_2O+""^(+)NO_2 + HSO_4^-`

The `"nitronium ion"`, `""^+NO_2`, in which the nitrogen is formally quaternized, is a potent electrophile, and can react with aryl species to give nitrated rings.