Mechanistic aspects of uncatalyzed and ruthenium(III) catalyzed oxidation of dl-ornithine monohydrochloride by silver(III) periodate complex in aqueous alkaline medium

The oxidation of an amino acid, dl-ornithine monohydrochloride (OMH) by diperiodatoargentate(III) (DPA) was carried out both in the absence and presence of ruthenium(III) catalyst in alkaline medium at 25 °C and a constant ionic strength of 0.10 mol dm−3 spectrophotometrically. The reaction was of first order in both catalyzed and uncatalyzed cases, with respect to [DPA] and was less than unit order in [OMH] and negative fraction in [alkali]. The order with respect to [OMH] changes from first order to zero order as the [OMH] increases. The order with respect to Ru(III) was unity. The uncatalyzed reaction in alkaline medium has been shown to proceed via a DPA–OMH complex, which decomposes in a rate determining step to give the products. Where as in catalyzed reaction, it has been shown to proceed via a Ru(III)–OMH complex, which further reacts with two molecules of DPA in a rate determining step to give the products. The reaction constants involved in the different steps of the mechanisms were calculated for both the reactions. The catalytic constant (KCat.const.) was also calculated for catalyzed reaction at different temperatures. The activation parameters with respect to slow step of the mechanism and also the thermodynamic quantities were determined.