nitration

Nitration is a chemical process that introduces a nitro group (-NO2) into an organic molecule, typically by electrophilic substitution on aromatic rings. The most common method uses a mixture of concentrated nitric acid and sulfuric acid, which generates the nitronium ion (NO2+) as the active electrophile.

In arenes such as benzene, NO2+ attacks the π-system to form a sigma complex, which then loses a proton to restore aromaticity, yielding nitrobenzene. The reaction is highly exothermic and is usually conducted at low temperatures (often 0–5 °C) to minimize poly-nitration and side reactions. The sulfuric acid serves both as solvent and catalyst, and the acid mixture can also influence the equilibrium and rate of the reaction.

Scope and selectivity depend on the substituents on the ring. Electron-donating groups tend to direct nitration to ortho and para positions, while electron-withdrawing groups direct meta. Substituents that deactivate the ring reduce reactivity, and higher temperatures or excess nitrating agents raise the risk of forming poly-nitrated products. While most nitration chemistry is discussed in the context of arenes, other substrates can undergo nitration under appropriate conditions, though these are less common in typical demonstrations.

Applications and significance: Industrially, nitration yields prototypes such as nitrobenzene and nitrotoluenes, which are precursors to anilines, dyes, and various specialty chemicals. Nitro compounds also include precursors to explosives and pharmaceuticals. Safety concerns are important: nitration is highly exothermic, uses strongly corrosive acids, and requires careful temperature control, proper ventilation, and strict waste handling.