Aqueous Ferrate(V) and Ferrate(IV) in Alkaline Medium: Generation and Reactivity

摘要

This chapter reviews the generation of ferrate(V) and ferrate(IV) complexes in basic solutions. Ferrate(V) (Fe~VO_4~(3-) is easily produced by the one-electron reduction of the relatively stable Fe~(VI)O_4~(2-) ion. Comparatively, generation of a ferrate(IV) complex via one-electron oxidation of Fe(III) is rather difficult, due to the relative insolubility of Fe(III) hydroxides and the slow oxidation rate. This has resulted in limited studies of the reactivity of ferrate(IV). The most studied aquated ferrate(IV) complex is ferrate(IV)-pyrophosphate. The reactivity of ferrate(IV) and ferrate(V) complexes with inorganic and organic substrates in alkaline solution is presented. The reactions of ferrate(IV)-pyrophosphate complex with pyrophosphate complexes of divalent metal ions are likely occurring through inner-sphere electron transfer. Ferrate(V) reacts with substrates predominantly via a two-electron transfer process to Fe(III). The only known example of one-electron reduction of ferrate(V) is its reactivity with cyanide in which sequential reduction of Fe(V) to Fe(IV) to Fe(III) was demonstrated. The reaction of Fe(V) with cyanide thus provides an opportunity for selective and unambiguous production of quantitative amounts of Fe(IV) in aqueous media.