Kinetic Study of the Oxidation of N,N-Dimethylethanolamine by Bis(Hydrogenperiodato)Argentate(III) in Aqueous Solution

Abstract

The oxidation of N,N-dimethylethanolamine (DMEA) by bis(hydrogenperiodato) argentate(III) ([Ag(HIO6)2]5−) was studied in aqueous alkaline medium. Formaldehyde and dimethylamine were identified as the major oxidation products after the oxidation of DMEA. The oxidation kinetics was followed spectrophotometrically in the temperature range of 25.0 °C–40.0 °C. It was found that the reaction was first order in [Ag(III)]; the oberved first-order rate constants kobsd as functions of [DMEA], [OH−] and total concentration of periodate (\([\mathrm{IO}_{4}^{-}]_{\mathrm{tot}}\)) were analyzed and were revealed to follow a rate expression: \(k_{\mathrm{obsd}} = (k_{1} +k_{2}[\mathrm{OH}^{-}])K_{1}K_{2}[\mathrm{DMEA}]/\{f([\mathrm{OH}^{-}])[\mathrm{IO}_{4}^{-}]_{\mathrm{tot}}+ K_{1} + K_{1}K_{2}[\mathrm{DMEA}]\}\). Rate constants k1 and k2 and equilibrium constant K2 were derived; activation parameters corresponding to k1 and k2 were computed. In the proposed reaction mechanism, a peridato-Ag(III)-DMEA ternary complex is formed indirectly through a reactive intermediate species [Ag(HIO6)(OH)(H2O)]2−. In subsequent rate-determining steps as described by k1 and k2, the ternary complex decays to Ag(I) through two reaction pathways: one of which is spontaneous and the other is prompted by an OH−.