nitrating

Nitrating is the chemical process of introducing nitro groups (-NO2) into organic molecules, most commonly by electrophilic aromatic substitution on aromatic rings. The standard nitrating system is a mixture of concentrated sulfuric acid and concentrated nitric acid, which generates the nitronium ion (NO2+), the active electrophile. Other nitrating reagents include nitronium salts and alternative acid systems, but the H2SO4/HNO3 mixture remains the most widely used.

In aromatic nitration, NO2+ attacks the π-system of the substrate, forming a sigma complex that loses a proton to restore aromaticity, yielding nitro-substituted products such as nitrobenzene. The reaction is exothermic and temperature-sensitive; typical conditions keep the reaction cold to limit poly-nitration. Substituents on the ring influence regioselectivity and rate: electron-donating groups accelerate nitration and direct to ortho/para positions, while electron-withdrawing groups slow the reaction and can direct to meta positions or suppress reaction.

Nitration is also used on aliphatic substrates under radical or ionic conditions, though this is less common and often requires different reagents. Nitro groups are versatile in synthesis and serve as placeholders for further transformations (reduction to amines, formation of aldehydes and carboxylic acids, or displacement in some contexts). The method is industrially important for the production of nitroaromatics used in dyes, pharmaceuticals, and explosives (for example TNT from toluene derivatives).

Safety and environmental considerations: nitration mixtures are highly acidic and generate nitrogen oxides; proper containment, cooling, and waste handling are essential.