Determination of the Critical Micelle Concentration of Imidazolium Ionic Liquids in Aqueous Hydrogen Peroxide

The critical micelle concentrations (CMC) of several imidazolium ionic liquids were measured in aqueous H2O2 (50 wt.% in H2O) by tensiometry, conductometry, and by the rate of catalytic epoxidation of cyclooctene, which is strongly enhanced as soon as micelles are formed. The CMC values in H2O2 were significantly lower compared to values in pure water reported in literature. In both cases, the CMC decreases with increasing alkyl chain length and increases with rising temperature. The degree of micelle ionization of 1-methyl-3-octylimidazolium tetrafluoroborate ([OMIM][BF4]) was calculated by conductometry (22-70 °C).