Kinetic and mechanistic study of ruthenium(III) catalysed and uncatalysed oxidation of oxalic acid by acid bromate

Acid bromate-oxalic acid reaction in the presence of mercury(II)- a bromide ion scavenger, is slow and exhibits first order each in [oxidant[, [oxalic acid[ and [mineral acid[. The proposed mechanism assumes a slow rate determining formation of an oxalyl-bromate ester, followed by the fast decomposition to products. The same reaction in the presence of Ru(III) is accelerated and exhibits fractional order each in [substrate[, [catalyst[ and [acid[ and first order in [bromate[. The proposed mechanism for catalysed reaction assumes a complex formation between oxalic acid and Ru(III), which subsequently undergoes decarboxylation after interacting with bromate. The mechanisms, for over all, catalysed and uncatalysed reactions are critically examined and values of rate constants of each reaction are evaluated. Activation parameters for all the reactions are also evaluated and discussed. (author). 24 refs., 2 tabs