Ionic liquid surfactants as multitasking micellar catalysts for epoxidations in water

Abstract

We present a single-component catalyst system for the epoxidation of hydrophobic olefins in aqueous solution. The aggregation of surface-active 1-alkyl-3-methylimidazolium ionic liquids (IL) containing the catalytically active tungstate dianion leads to micelles, which solubilise apolar olefins in aqueous media. The micellisation of tungstate allows for the epoxidation of cyclooctene and other olefins in water, using environmentally benign hydrogen peroxide as oxidant. The structural characterisation of the micelles under catalysis conditions as well as the substrate uptake have been studied by cryo-TEM. ¹⁸³W-NMR studies revealed that the catalytically active species is a tetraperoxotungstate complex. The addition of organophosphonic acids results in a significant boost of the catalytic activity by formation of a tungstate–phosphonate adduct, investigated using electrospray ionisation mass spectrometry (ESI-MS). The versatile functionalisability of the imidazolium cation enables a covalent linkage of a phosphonate group, which is further increasing the catalytic activity.