Kinetics of the oxidation of 2,3-dimethylbutane-2,3-diol by bis(2,2′-bipyridine)silver(II) ions in aqueous nitrate media
Abstract
The stoichiometry and the kinetics of the oxidation of 2,3-dimethylbutane-2,3-diol (pinacol) by [Ag(bipy)2]2+ ions have been investigated. It is shown that the oxidation proceeds through intermediate complexes involving AgII and pinacol. Although [Ag(bipy)2]2+ itself is eliminated as a participant in these oxidatively active complexes, [Ag(bipy)(pinacol)]2+ remains as a possible intermediate. The kinetics show that one of the principal pathways involves Ag2+aq complexed with un-ionised pinacol, but they do not distinguish between the involvement of [Ag(bipy)(pinacol)]2+ and [Ag2+(CH3)2COH·(CH3)2CO–] in the other principal path: the linear Arrhenius plots suggest that the latter two are alternatives and not parallel courses. Values for the enthalpies and entropies of activation are determined. This oxidation is compared with the oxidation of other substrates by [Ag(bipy)2]2+; the pathway involving oxidation by Ag2+ with all the bipyridine removed is compared with the oxidation of other substrates by Ag2+aq and the oxidation of pinacol and other substrates by other aquacations.