Kinetics and mechanisms of oxidation by metal ions. Part XIV(1). Osmium(VIII)-catalysed oxidation of cycloalkanones by alkaline hexacyanoferrate(III)

Abstract

The OsVIII-catalysed oxidation of cyclopentanone and cyclohexanone by alkaline hexacyanoferrate(III) ions is zeroth-order with respect to $ {⤪ F_{e}(CN)_{6}^{3-} $ and first-order with respect to [OH−]. The dependence of ko, the pseudo zero-order rate constant with respect to $ {⤪ F_{e}(CN)_{6}^{3-} $, on [OsVIII] is given by: ko = a + b[OsVIII]. The primary product in the oxidation of cyclohexanone (cyclohexanone in an excess) is the corresponding α-hydroxyketone which, in an excess of [Fe(CN)6]3−, is oxidised to adipic acid. The rate data analysis indicated that the keto form of the ketone is oxidised by OsVIII, a two electron equivalent oxidant, in alkaline medium. This result is the opposite of the trend observed in acid.