The Autooxidation of Hydrazine

The redox reactions of hydrazine toward main-group and transition metal oxidants have been reviewed (73). Different stoichiometries have been found, with N2 appearing as the N-containing oxidized product, sometimes accompanied by the formation of NH3 and/or HN3. The mechanisms have been analyzed in terms of the one- or two-electron nature of the oxidants, and imply both outer-and inner-sphere routes, depending on the oxidant. The very reactive, key intermediate, diazene (diimide), N2H2, has been proposed in most of these reactions. 

The reaction with 02 is absent from these studies. It turns out that the autoxidation reaction should be a very slow process because of 

The high lability of bound N2 in [FeII(CN)5N2]3 regenerates the active site, namely the [FeII(CN)5H20]3 ion, which is able to further bind and process hydrazine. A more detailed kinetic study could be warranted for this interesting set of reactions. Some uncertainties still remain as to the nature of the intramolecular electron-transfer rate processes (91). At the employed concentration levels of the complex, the participation of mixtures of mononuclear and dinuclear complexes complicate the spectral evolution. Even the nature of the dinuclear intermediates (cyano- or hydrazino-bridged) could be put into question (probably both are involved, due to the labile interconversion equilibria). The participation of Fe(III) species, either in the mononuclear or dinuclear species, as reactive intermediate precursors of the formation of diazene and N2 

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It has been reported (69TL5005) that an ESR spectrum was observed during the autooxidation of the aqueous alkaline solution of 3 in the presence of hydrazine. This spectrum was said to be due to structure 43, based on the structure of monodehydro-L-ascorbic (44) (Scheme 9). When that structure was revised to 45, it was deduced that pyrrole ring structures 43 were not formed (74CPB1417). Further studies of the reaction in an aerobic alkaline aqueous solution gave rise to some radical intermediates. 

Stone, D. A. "The Vapor Phase Autooxidation of Unsymmetrical DimethyIhydrazine and 50 Percent Unsymmetrical Dimethyl-hydrazine-50 Percent Hydrazine Mixtures," Report No. ESL-TR-80-21, April 1980. 

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