KINETICS AND MECHANISM OF RUTHENIUM(III) CATALYZED OXIDATION OF ETHANOL BY CERIUM(IV) IN AQUEOUS SULFURIC-ACID MEDIA

The kinetics of oxidation of ethanol by cerium(IV) in presence of ruth enium(III) (in the order of 10(-7) mol dm(-3)) in aqueous sulfuric aci d media have been followed at different temperatures (25-40 degrees C) . The rate of disappearance of cerium(ni) in the title reaction increa ses sharply with increasing [C2H5OH] to a value independent of [C2H5OH ] over a large range (0.2-1.0 mol dm(-3)) in which the rate law confor ms to: [GRAPHICS] where [Ru](T) gives the total ruthenium(III) concent ration. The values of 10(-3)k(c) and 10(-3)k(d) are 3.6 +/- 0.1 dm(3) mol(-1) s(-1) and 3.9 +/- 0.2 s(-1), respectively, at 40 degrees C, I = 3.0 mol dm(-3). The proposed mechanism involves the formation of rut henium(III)(-) substrate complex which undergoes oxidation at the rate determining step by cerium(IV) to form ruthenium(IV)(-) substrate com plex followed by the rapid red-ox decomposition giving rise to the cat alyst and ethoxide radical which is oxidized by cerium(IV) rapidly. Th e mechanism is consistent with the existence of the complexes Ru-III.( C2H5OH) and Ru-III.(C2H5O-] and both are kinetically active. The overa ll bisulphate dependence conforms to: k(ohsd) = A[Ru](T)/{1 + C[HSO4-] } where A = 2.2 x 10(4) dm(3) mol(-1) s(-1), C = 1.3 at 40 degrees C, [H+] = 0.5 mol dm(-3), and I = 3.0 mol dm(-3). The observations are co nsistent with the Ce(SO4)(2) as the kinetically active species. (C) 19 95 John Wiley & Sons, Inc.