Aromatic Nitration

Theory
Problems and exercises
Solutions
Where I am
Molecular panel (opens in a new tab)

The nitration of an aromatic ring cannot be achieved with nitric acid alone. Nitric acid has to be "activated" by making it react first, as a base (!), with sulfuric acid, a stronger acid.

Nitration of benzene with HNO₃ and H₂SO₄: nitrobenzene

Even though nitric acid is usually considered as a quite strong acid, since acidity is a relative concept, HNO₃ behaves as a base when confronted with stronger acids like sulfuric acid.

Formation of the nitronium ion: nitric acid acts as a base, is protonated by H₂SO₄ and loses water to give NO₂⁺

The nitronium ion is an excellent electrophile that can be attacked by the π cloud of benzene, leading to nitrobenzene. Notice that sulfuric acid is recovered and thus only a catalytic amount of it, not a stoichiometric one, is needed.

Attack of benzene on the nitronium ion: the benzenonium ion forms and loses a proton, taken up by HSO₄⁻, to give nitrobenzene