Question

Can nitric acid be protonated?

Answer 1

In highly acidic media, nitric acid can be protonated.

Explanation:

This is the basis for the nitrating mixture used to prepare nitro-arenes:

`H_2SO_4(aq) + HNO_3(aq) rarr HSO_4^(-) +H_2NO_3^+`

`H_2NO_3^+ rarr NO_2^+ + H_2O`

The nitronium ion is a very potent electrophile because of the quaternized nitrogen centre in `O=N^+=O`. As to how to quantify this basicity, you have got me. We use a highly electrophilc (i.e. acidic) medium to produce the nitronium ion.

The nitronium ion is produced by these means in explosives manufacture when toluene is nitrated, to produce `"trinitrotoluene"`. I have no doubt it is safe but it is something I would not like to do.