nitroalkanes

Nitroalkanes are a class of organic compounds in which a nitro group (–NO2) is bonded to an sp3-hybridized carbon of an alkyl or aryl group. The general motif is R-CH2-NO2, which includes nitromethane (R = H), nitroethane (R = CH3), and other higher nitroalkanes. The nitro group is highly electron-withdrawing, giving nitroalkanes distinctive reactivity and polarity.

Industrial and laboratory preparation of nitroalkanes typically involves nitration of alkanes or alkyl halides under strongly acidic conditions to install the nitro group. Alternative routes include nucleophilic substitutions using nitrite sources to form R-NO2 directly on the carbon skeleton. These methods yield a range of nitroalkanes that serve as versatile building blocks in organic synthesis.

The chemistry of nitroalkanes is dominated by the acidity of the alpha protons. Deprotonation gives nitronate anions, which are useful intermediates for carbon–carbon bond-forming reactions and other transformations. Nitroalkanes participate in Henry (nitroaldol) reactions with aldehydes or ketones to form β-nitro alcohols, and they can be transformed further by reductions of the nitro group to primary or secondary amines. Other transformations include oxidation, substitution, and rearrangements that exploit the electron-withdrawing nitro group.

Physical properties of nitroalkanes vary with chain length and substituents; many are colorless liquids or solids at room temperature and are relatively polar, often soluble in organic solvents and, for lower members, moderately soluble in water. They can pose hazards due to the energetic nature of nitro compounds and the exothermicity of nitration reactions, so proper handling and temperature control are important.

Applications of nitroalkanes include their use as solvents (notably certain nitroalkanes) and as versatile reagents and intermediates in pharmaceutical, fragrance, and polymer chemistry, where they provide access to amines, alcohols, and other functional groups.