Reduction to hydroxylamines

Partial reduction to hydroxylamines may also be involved in the degradation of nitroarenes ... 

Nitration opens up another pathway to metabolic activation. Nitro-PAHs are wide-spread environmental pollutants that are mutagenic and carcinogenic. Metabolism of nitro-PAHs could occur via nitro-activation (reduction to hydroxylamine, eventually leading to nitrenes that can bind to nucleotides) and/or by ring oxidation and formation of DEs. ... 

Spin traps also exhibit site-specific radical reactions [56]. The water-soluble spin trap DMPO can only trap the OH produced extracellularly, whereas the lipophilic spin trap PBN can trap intracellular OH (Fig. 1). Spin adducts can also undergo enzymatic and chemical reduction to hydroxylamines[57]. The localization of spin adducts and hydroxylamines is dependent upon their partition coefficients. 

Selective reduction to hydroxylamine can be achieved in a variety of ways the most widely applicable systems utilize zinc and ammonium chloride in an aqueous or alcoholic medium. The overreduction to amines can be prevented by using a two-phase solvent system. Hydroxylamines have also been obtained from nitro compounds using molecular hydrogen and iridium catalysts. A rapid metal-catalyzed transfer reduction of aromatic nitroarenes to N-substituted hydroxylamines has also been developed the method employs palladium and rhodium on charcoal as catalyst and a variety of hydrogen donors such as cyclohexene, hydrazine, formic acid and phosphinic acid. The reduction of nitroarenes to arylhydroxyl-amines can also be achieved using hydrazine in the presence of Raney nickel or iron(III) oxide. ... 

Reduction of methyl [5-(bromomethyl)isoxazolidin-3-yl]acetates 324 with trihutyltin hydride in boiling toluene in the presence of AIBN led to opening of the isoxazolidine ring and formation of isoxazolidinones 579. The process is believed to go through the formation of nitroxide radical 577, followed by reduction to hydroxylamine 578 and cyclization to 579 with elimination of methanol (Equation 98) <1999SL79>. 

Aromatic nitro compounds may generally be reduced in a four-electron reduction to hydroxylamines, which in acid solution at a more negative potential can be reduced further to amines. By choosing a suitable cathode potential it is thus possible to avoid the further reduction of the hydroxylamine to the amine. When a hydroxyl or amino group is ortho or para to the nitro group, it is not feasible to isolate the hydroxylamino compound, as it is too easily dehydrated to the reducible quinone mono- or diimine. It may, however, be possible to trap the intermediate. 

C) Reduction to Hydroxylamines. Place in an eight-inch tube 1 ml of nitrobenzene, 20 ml of water, and 0.6 g of ammonium chloride. Add in small portions 1.6 g of zinc dust, shaking the contents of the tube. The reduction of nitrobenzene to j6-phenylhy-droxylamine proceeds rapidly with evolution of heat, and the temperature rises to 50-60°. When all the zinc dust has been added, shake the tube for a few minutes longer, filter the zinc oxide and wash with 2-3 ml of hot water. Add to the filtrates 6 g of salt,... 

Under suitable conditions it is possible to isolate the A-substituted hydroxylamines that are formed as intermediates in the reduction of nitro compounds. For this purpose it is essential in the reduction of aromatic nitro compounds to work with neutral or nearly neutral solutions suitable reducing agents are hydrogen and platinum oxide catalysts in glacial acetic acid,82,83 zinc dust in ammonium chloride solution,84 aluminum amalgam,85 and ammonium sulfide.86 Aliphatic nitro compounds may be reduced as their alkali salts (nitronates) by diborane in tetrahydrofuran, then giving A-alkylhydroxyl-amines 87 for instance, A-cyclohexylhydroxylamine is thus obtained from nitrocyclohexane in 53% yield. However, aliphatic nitro compounds are converted into A-alkylhydroxylamines more simply by catalytic hydrogenation in the presence of palladium-barium sulfate unlike aromatic nitro compounds, aliphatic nitro compounds require an acid medium for reduction to hydroxylamines an oxalic acid medium has proved the most suitable. 

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