Kinetics and Mechanism of Permanganate Oxidations of Isosorbide in Different Acidic Media

Abstract

The oxidation kinetics of isosorbide (S) by potassium permanganate in both perchloric and sulfuric acid solutions was investigated spectrophotometrically at a constant ionic strength of 2.0 mol·dm−3 and at 25 °C. In both acids, the oxidation reactions showed a first-order dependence on \([{\text{MnO}}_{4}^{ - }]\), apparent a less than unit-order dependence with respect to [S] and a fractional-second-order dependence with respect to [H+]. Variation of either the ionic strength or dielectric constant of the reactions media did not significantly affect the oxidation rates. In both acids, the final oxidation product of isosorbide was identified by both spectroscopic and chemical tools as the corresponding monoketone derivative, namely (1S,4S,5R)-4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. Under comparable experimental conditions, the oxidation rate of isosorbide in perchloric acid was lower than that in sulfuric acid. The oxidation mechanism describing the kinetic results was proposed and the rate law expression was derived. The activation parameters of the second-order rate constants were computed and are discussed.