Laboratory preparation of nitrobenzene

Aromatic compounds can be directly nitrated using a mixture of concentrated nitric acid and sulphuric acid.

This reaction is an example of electrophilic substitution of benzene. The electrophile is a nitronium

ion.

The nitronium ion attacks to the benzene ring resulting in the formation of a carbocation. Electron releasing substituents like -CH₃, -OCH₃, -OH, -NH₂ etc activate the ring and stabilize the carbocation while electron withdrawing groups like -NO₂, -CN, -SO₃H, -X activate the carbocation. The nitrating mixture of conc H₂SO₄ and conc HNO₃ con nitrate even deactivated compounds like nitrobenzene under refluxing conditions to get m-dinitrobenzene. For nitration of activated aromatic systems like phenol and then ether derivatives, even milder conditions can be used.