Mononitration

MonoNitration is the chemical process of introducing a single nitro group (-NO2) into an organic substrate, most commonly an aromatic ring, to yield a mono-nitrated product. It is a classic example of electrophilic aromatic substitution, proceeding via generation of the nitronium ion (NO2+) in a mixture of concentrated nitric acid and sulfuric acid, followed by attack on the aromatic π system and deprotonation to restore aromaticity.

Typical conditions and scope: The reaction uses concentrated nitric acid and sulfuric acid, with the nitronium ion acting as the electrophile. Reactions are often conducted at low temperature (around 0 to 5 °C for simple arenes) to minimize over-nitration and side reactions such as sulfonation. The amount of nitrating mixture, temperature, and reaction time influence whether mono- or polysubstitution occurs. Higher temperatures or longer times increase the risk of forming dinitro or polynitrated products.

Regioselectivity and substituent effects: The position of the introduced nitro group is governed by substituents already on the ring. Activating groups direct electrophilic attack to ortho and para positions, while strongly deactivating or meta-directing substituents bias the reaction toward meta substitution and reduce overall reactivity. In benzene, nitration yields nitrobenzene; in toluene, mainly ortho- and para-nitrotoluenes; in phenols and anisoles, ortho/para positions are often favored under appropriate conditions.

Purification and applications: The mono-nitrated product is typically isolated by aqueous workup and purified by distillation or chromatography. Mono-nitration products serve as important intermediates for further transformations, such as reduction to amines or conversion to other functional groups. Safety considerations include the exothermic nature of nitration and the hazards associated with concentrated acids and mixed reagents, requiring careful temperature control and proper waste handling.