Kinetics and mechanism of oxidation of D-ribose, D-glucose, and D-fructose by dichloroisocyanuric acid in aqueous acetic acid-perchloric acid mixtures catalyzed by Ru(III)

摘要

The kinetics and mechanism of oxidation of D-ribose, D-glucose, and D-fructose by dichloroisocyanuric acid (DCICA) in aqueous acetic acid-perchloric acid mixtures catalyzed by Ru(III) have been investigated. The oxidation of D-ribose and D-glucose has the following kinetic orders: first order in oxidant, first order in Ru(III), and zeroth order in substrates and H+. The D-fructose exhibits a different behavior: zeroth order in oxidant, first order in catalyst, and zeroth order in substrate and H+. The results have been rationalized by postulating an active Ru(V) species, which oxidizes the pentose and hexose in a fast step to products. D-fructose reacts by complexation with Ru(III) in an equilibrium step, and the complex breaks down into products without involvement of DCICA. The Ru(III) species is regenerated by DCICA in a fast step, which acts as a catalyst continuously. The mechanistic pathway seems to be different in aldose and ketose systems. It is presumed that beta-anomer in all-cases is reacting with either Ru(V) or Ru(III) species, yielding products. The corresponding lactones are the products in each case along with formaldehyde in case of D-fructose under the conditions of [sugar] > [DCICA].