nitrations

Nitrations are chemical reactions that introduce a nitro group (−NO2) into a substrate, most commonly an aromatic or aliphatic hydrocarbon. The term covers electrophilic aromatic nitration as well as other methods that attach nitro groups to organic frameworks. Nitro compounds are widely used as intermediates in the synthesis of dyes, pharmaceuticals, agrochemicals, and explosives, among other applications.

In aromatic nitrations, the nitro group is introduced by the nitronium ion (NO2+), generated in situ from a mixture of concentrated nitric acid and sulfuric acid. The reaction proceeds by electrophilic substitution on an electron-rich aromatic ring, forming a sigma complex, followed by deprotonation to restore aromaticity and yield a nitroarene (for example, nitrobenzene). Regioselectivity is governed by substituents on the ring: electron-donating groups direct electrophilic attack to ortho or para positions, while electron-withdrawing groups tend to direct meta positions for subsequent substitutions. The nitro group itself is strongly deactivating and meta-directing for further nitrations.

Aliphatic nitrations are less common and typically proceed via radical or ionic mechanisms under harsh conditions, yielding nitroalkanes. These routes are generally more difficult to control and less selective than aromatic nitration, but they provide routes to nitrated aliphatic compounds that do not possess activated aromatic rings.

Industrially, nitration is a prominent transformation in the production of nitroaromatics, including intermediates for dyes, pharmaceuticals, and energetic materials, such as trinitrotoluene (TNT). Safety and environmental considerations are central, as nitration is highly exothermic and uses corrosive acids with emissions of nitrogen oxides; proper temperature control and waste management are essential.