Nitroarene reduction
Abstract
The catalytic hydrogenation of a nitroarene is one of the most common methods for the synthesis of anilines. The reaction is typically carried out using molecular hydrogen (H2) in the presence of a metal catalyst such as palladium on carbon (Pd/C), platinum (Pt), Raney nickel, or rhodium (Rh).
Keywords
Nitroarene, Reduction, Aniline
Category
Aromatic
Mechanism
Mechanistically, both hydrogen and the nitro compound adsorb onto the surface of the metal catalyst. The H–H bond is activated by the metal and dissociates into adsorbed hydrogen atoms. The nitro group is then reduced through a sequence of hydrogenation steps involving nitroso (Ar–NO) and hydroxylamine (Ar–NHOH) intermediates. At each stage, hydrogen atoms are transferred from the catalyst surface to the intermediate, progressively reducing the N–O bonds. Catalytic hydrogenation is generally highly chemoselective and atom-economical, since molecular hydrogen serves as the reductant and no stoichiometric metal waste is generated. However, other reducible functional groups such as alkenes, alkynes, benzyl protecting groups, or certain carbonyl derivatives may also undergo reduction under the reaction conditions, depending on the catalyst employed.
