KINETICS AND MECHANISM OF ZnCl2 CATALYSED OXIDATION OF ORGANIC SULFOXIDES BY PERMANGANATE IN NON- AQUEOUS MEDIUM

Abstract: The rates and mechanism of zinc chloride (Lewis acid) catalysed oxidation of several organic sulfoxides by permanganate have been studied in anhydrous acetone solutions. The kinetic rate law obtained indicates that a complex between permanganate and the Lewis acid (ZnCl2) is formed before oxidation of the sulfoxides occurs. The function of the zinc chloride is to enhance the reactivity of permanganate. A Hammett ρ value of-2.1 8 ± 0.09 is obtained for the oxidation of sulfoxides at 23.0 0C. A negative ρ value means that the sulfur is electron deficient in the transition state. Values for the HOMO energies of sulfoxides and the LUMO energies for permanganate ion and the permanganate-zinc chloride complex have been calculated. The results indicate that electron donating substituents on the ring increase the rate of the reaction and electron withdrawing groups slow down the reaction