Nitroso compound dimers hydroxylamines

Although electrochemical oxidation of Al-cyclohexyl-Al-hydroxylamine in the presence of pyridine afforded the corresponding dimeric nitroso compound with a low yield, A-hydroxy t-alkylamines were transformed into the corresponding nitroso compounds (equation 8) . Similarly, A-phenylhydroxylamine was transformed into nitrosobenzene under similar reaction conditions. ... 

Both aromatic and aliphatic nitroso compounds have been prepared by oxidative procedures. While few of the methods can be considered generally applicable, a sufficient variety of reagents have been proposed that it would appear reasonable to state that virtually any nitroso compound may be prepared by one of these procedures. The organic substrates which have been used are oxaziranes and imines, amines, hydroxylamines, and oximes. A byproduct of the oxidation of 4-methylcinnoline (an azo compound) has also been identified as a dimeric nitroso compound. 

Aromatic and aliphatic primary amines can be oxidized to the corresponding nitro compounds by peroxy acids and by a number of other reagents. The peroxy acid oxidations probably go by way of intermediate hydroxylamines and nitroso compounds (Scheme 2). Various side reactions can therefore take place, the nature of which depends upon the structure of the starting amine and the reaction conditions. For example, aromatic amines can give azoxy compounds by reaction of nitroso compounds with hy-droxylamine intermediates aliphatic amines can give nitroso dimers or oximes formed by acid-catalyz rearrangement of the intermediate nitrosoalkanes (Scheme 3). 

Oximes are reduced in benzene solution to hydroxylamines by sodium borohydride adsorbed on silica gel. In turn, silver carbonate on Celite cleanly oxidizes hydroxylamines to C-nitroso-compounds, isolate as nitroso-dimers no oximes are formed. Such dimers can be thermally dissociated to the more reactive monomers, whichare tautomerized to oximes on thermal or red-light treatment. ... 

Oxidative reactions of organonitrogen species that do not involve molecular oxygen are rather limited. The only case for which the evidence is at all convincing is the oxidation of arylhydroxylamines to arylnitroso species (Table 2). This reaction resembles the first half of the hydroxylamine oxidoreductase reaction found in nitrifying bacteria. The key difference is that the aryl nitroso compound is stable (although condensation with the arylhydroxy-lamine can occur to produce the azoxy compound, ArN(O)NAr), while the inorganic analog is nitroxyl, HNO, which if released from the enzyme would rapidly dimerize and dehydrate to form N2O. Consequently, HAO does not release the HNO or NO intermediate, but instead oxidizes it to nitrite before any substrate-derived species are released. 

The reaction of nitroalkanes and dinitroalkanes with sodium hydrogen telluride gives nitrosoalkane dimers and olefins, respectively.96 The reduction of other nitrogenated species such as hydroxylamines, azides, nitroso, azo, and azoxy compounds can also be performed by using tellurium reagents.6,11,12... 

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