Kinetics and mechanistic approach to electron transfer from renewable isosorbide to Ce (IV) in HClO4 medium

Abstract

Kinetics of isosorbide (S) oxidation by Ce(IV) in aqueous HClO4 medium has been examined via spectrophotometric technique at fixed ionic strength and temperature. The reaction showed a 1: 2 stoichiometry (S: Ce(IV)). The reaction was studied under pseudo-first order conditions. The dependency of the rate of oxidation reaction on the reactants’ concentrations showed that the reaction was first order in [Ce(IV)], whereas in both [H+] and [S], its order was lower than unity. The oxidation rate was directly proportional to ionic strength as well as dielectric constant of the reaction medium. However, it should be mentioned that adding Ce(III) had remarkably not affect the rate. The isosorbide oxidation product was recognized as (1S,4S,5R)-4-hydroxy-2,6-dioxabicyclo[3.3.0]octan-8-one). A mechanistic scheme for oxidation coherent with the observed kinetics was proposed. The rate-law expression was derived which was agreed with the acquired outcomes. The calculated activation quantities recommended construction of a rigid intermediate through the reaction and such process was endothermic and non-spontaneous.