Formation of a catalytically active intermediate for oxidation in H2O2/ionic liquid system: experimental and theoretical investigations

Abstract

A metal-free method for activation of hydrogen peroxide (H2O2) is introduced using piperidinium trifluoroacetate (PPHTFA) ionic liquid as catalyst. The catalyst has been used for selective oxidation of thioanisole to its corresponding sulfoxide at room temperature. It was found that the selectivities were reduced by increasing the reaction temperature. In this work, no organic solvents or metallic salts were used for activation of H2O2. Mechanistic studies suggested that the reaction proceeds via in situ formation of trifluoro hydroperoxy species as an active catalytic intermediate. Formation of the catalytic intermediate was screened by NMR, IR and Mass Spectroscopy analysis. Density functional theory calculations at B3LYP/6-31+G* levels revealed that the origin of selectivity is the higher activation energy for overoxidation of sulfoxide at room temperature. The catalyst was recovered and reused with excellent selectivity.