Silver(III) Periodate Complex—An Oxidant for Free Radical Induced Uncatalyzed and Ruthenium(III) Catalyzed Oxidation of Barbituric Acid

The oxidation of a heterocyclic compound—barbituric acid (BBA) by diperiodatoargentate(III) (DPA) was carried out in the absence and presence of ruthenium(III) catalyst in alkaline medium with a constant ionic strength of 0.20 mol dm –3 at 298 K. The reaction was monitored spectrophotometrically. The reaction was of first order with respect to [DPA] and was less than unity order with respect to [BBA] in both catalyzed and uncatalyzed cases. Positive and negative fractional order in [OH – ] for uncatalyzed and Ru(III) catalyzed reaction respectively was observed, whereas perioadate has retarding effect in both the cases. A unity order with respect to [Ru(III)] was observed. The uncatalyzed reaction in alkaline medium has been shown to proceed via a DPA–BBA complex, which decomposes in a rate determining step to give the free radicals, which is followed by other fast steps to give the products. Whereas in catalyzed reaction, it has been shown to proceed via a Ru(III)–BBA complex, and similar other steps as in uncatalyzed reaction to give the products. The reaction constants involved in the various steps involved in the mechanisms were calculated for both the reactions. The catalytic constant ( k C ) was also calculated for catalyzed reaction at four temperatures. The activation parameters with respect to slow step of the mechanism and also the thermodynamic data for all the equilibrium steps were determined and discussed.