KINETICS AND MECHANISMS OF OXIDATION BY METAL-IONS .14. OSMIUM(VIII)-CATALYZED OXIDATION OF CYCLOALKANONES BY ALKALINE HEXACYANOFERRATE(III)

The Os(VIII)-catalysed oxidation of cyclopentanone and cyclohexanone by alkaline hexacyanoferrate(III) ions is zeroth-order with respect to Fe(CN)6(3-) and first-order with respect to [OH-]. The dependence of k0, the pseudo zero-order rate constant with respect to Fe(CN)6(3-), on [Os(VIII)] is given by: k0 = a + b[Os(VIII)]. The primary product in the oxidation of cyclohexanone (cyclohexanone in an excess) is the corresponding alpha-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 Os(VIII), a two electron equivalent oxidant, in alkaline medium. This result is the opposite of the trend observed in acid.