Kinetics and mechanism of hexachloroplatinate(IV) reduction by some neutralized α-hydroxy acids in a carbonate-hydrogencarbonate buffer medium

Article abstract of DOI:10.1246/bcsj.73.553

The kinetics of hexachloroplatinate(IV) reduction by some neutralized α-hydroxy acids such as glycolic, lactic, α-hydroxyisobutyric, mandelic, atrolactic, and benzilic acids in a carbonate-hydrogencarbonate buffer medium have been investigated. Platinum(IV) is reduced by the substrates to platinum(II) in a one-step two-electron process, whereas the substrates are oxidized to give formaldehyde, acetaldehyde, acetone, benzaldehyde, acetophenone, and benzophenone for the respective reactions. The pseudo- first-order rate constant is independent of the initial [platinum(IV)] as well as [OH-]. The reaction rate increases with increasing [substrate], but decreases with increasing chloride concentration. The reactions obey the following rate expression: -d[Pt(IV)](t)dr=kK(e)[A^-][Pt(IV)]t/Cl^-]+K(e)A^- ]. The reactions proceed through an initial 1: 1 complex formation between the reactants, followed by decomposition of the complex to give the respective reaction products via C-C bond cleavage. The reactivity of the α- hydroxycarboxylate towards Pt(IV) are as follows: atrolactic acid > mandelic acid > benzilic acid > α-hydroxyisobutyric acid > lactic acid > glycolic acid. Thermodynamic parameters for the decomposition step have been evaluated. The mechanism of the reactions is discussed.