Hydrogenation to Nitroso or Hydroxyimino and Hydroxyamino Compounds

Examples of the hydrogenation of nitroalkanes to nitroso or hydroxylimio compounds are rather few. On the other hand, more examples are known for the hydrogenation of nitroalkanes to the corresponding hydroxylamines. 

Nitroguanidine was hydrogenated to nitrosoguanidine in yields of 56-59% over platinum oxide and in 37-44% yields over Raney Ni.26 Water was found to be most suitable as the reaction medium for the platinum catalyst (eq. 9.12). Over Raney Ni, somewhat greater rates and yields were obtained in methanol than in water. 

4-Nitro-2-methyl-3-butanol and l-nitro-2-octanol were hydrogenated in aqueous ethanol solution in the presence of oxalic acid and acetic acid, respectively, to give 76 and 69.5% yields of the hydroxylamine oxalates. In one patent, nitromethane (684 g, 11.2 mol) was hydrogenated over 2 g of 5% Pd-C in 60% aqueous H2S04 (1010 g, 6.18 mol)-toluene (684 g), as a water-immiscible solvent, at 50°C and 4.1 MPa H2 and a 92% of jV-methylhydroxylamine sulfate was obtained from the aqueous phase together with 6% of methylamine sulfate.29 

TABLE 9.2 The Effect of Temperature on Hydrogenation of Nitrocyclohexane over Silver-Zinc-Chromium Oxide  

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