Reaction mechanisms of hypervalent iron: The oxidation of amines and hydroxylamines by potassium ferrate

Hypervalent iron compounds are found in a number of systems ranging from redox enzymes to synthetic oxidants. In order to understand the function of iron in these processes the reactivity of the active species must be characterized. Unfortunately, for many systems the hypervalent iron adduct is a fleeting intermediate which makes the study of its chemistry difficult. One approach used by researchers to explore this chemistry is to oxidize iron(II) or iron(III) compounds with peroxide or other oxygen donors. Although catalytic activity is observed in some iron/peroxide systems, detailed mechanistic studies are problematic because the oxygen binding step is often difficult to separate from the redox reaction.;Rather than oxidizing iron compounds in situ we have approached hypervalent iron chemistry with a study of an isolable iron(VI) compound, potassium ferrate. To date many of the ferrate studies have been carried out from a synthetic point of view. Although these studies are important, a better understanding of hypervalent iron chemistry can be achieved through mechanistic studies. In order to probe these mechanisms, the reactions of ferrate with small nitrogen containing molecules has been initiated.;The reaction kinetics of aniline, hydroxylamine, N-methylaniline and benzylamine with potassium ferrate have been studied. For each oxidation there is evidence for the formation of an iron-substrate intermediate that is subject to different fates depending on the reaction conditions. The lifetime of the reactive intermediate is dependent upon the nature of the substrate and in some situations these intermediates are observed spectrally. This work not only provides information about the oxidation mechanisms associated with ferrate but also lends insight into the development of new high oxidation state iron compounds.