KINETICS OF CERIUM(IV)-D-FRUCTOSE REACTION IN THE PRESENCE OF AQUEOUS H_2SO_4 MEDIUM

摘要

The kinetics of cerium(IV) oxidation of D-fructose in aqueous H_2SO_4 medium has been studied spectrophotometrically.The reaction is first order in [Ce(IV)] in the presence of excess [D-fructose].The effect of H_2SO_4 on the UV-vis.spectrum of cerium(IV) is discussed.The overall process shows first order dependence on [D-fructose] whereas that in [H_2SO_4] is complex.The oxidation kinetics of D-fructose with cerium(IV) has indicated a rate-limiting bimolecular reaction between cerium(IV) and D-fructose leading to the formation of a free radical and Ce(III).Increase in [H_2SO_4] accelerates the reaction rate.The active oxidant (cerium(IV)-sulphato) and reductant species are H_4Ce(SO_4)_4 and beta-D-fructopyranose,respectively.The proposed mechanism corresponds to the rate law The reactivity of cerium(IV) has also been compared with chromium(VI) and vanadium(V).