Olefin Epoxidation in Aqueous Phase Using Ionic‐Liquid Catalysts

Abstract

Hydrophobic imidazolium-based ionic liquids (IL) act as catalysts for the epoxidation of unfunctionalized olefins in water using hydrogen peroxide as oxidant. Although the catalysts are insoluble in both the substrate and in water, surprisingly, they are very well soluble in aqueous H2 O2 solution, owing to perrhenate-H2 O2 interactions. Even more remarkably, the presence of the catalyst also boosts the solubility of substrate in water. This effect is crucially dependent on the cation design. Hence, the imidazolium perrhenates enable both the transfer of hydrophobic substrate into the aqueous phase, and serve as actual catalysts, which is unprecedented. At the end of the reaction and in absence of H2 O2 the IL catalyst forms a third phase next to the lipophilic product and water and can easily be recycled.

Ionic Liquids as Micellar Agents in Perrhenate‐catalysed Olefin Epoxidation

“…ReO 4 − was supposed to act as catalyst activating H 2 O 2 . The results of the catalytic experiments are shown in Figure in comparison to KReO 4 without surfactant and to the benchmark catalyst [OMIM]ReO 4 . After 6 h reaction time, conversion of the olefin is almost complete in case of [OMIM]BF 4 .…”

“…Cokoja et al. have recently reported on imidazolium‐based perrhenate ILs as bifunctional catalysts in the solvent‐free epoxidation of cyclooctene with aqueous H 2 O 2 . Here, the imidazolium cation takes the role of surfactant and solubilises the substrate while the ReO 4 − anion activates H 2 O 2 via an outer‐sphere mechanism .…”

Ionic Liquid-Based Microemulsions in Catalysis

“…12,13 More recently, the properties of catanionic ionic liquids, containing both anions and cations with hydrophobic tails, have proved to be exceptional. 14,15 Surface-active ionic liquids have already been well explored for a number of applications in synthesis, 16,17 catalysis 18,19 and separations 20,21 rendering them ideally suited for the development of targeted microemulsions, 22−26 and for their separation. 27 …”

Kinetic Model of Two‐Phase Epoxidation with Ionic Liquids as Micellar Catalysts

“…The catalyst and hence the micelles are only present in the aqueous phase, which was shown by solubility experiments at the onset of the reaction , corresponding to a Winsor I system.…”

“…This is why the reaction in the micellar pseudophase is modeled with an adapted enzyme‐kinetic (Michaelis‐Menten) approach. To do so, the following assumptions are made: The catalyst and hence the micelles are only present in the aqueous phase, which was shown by solubility experiments at the onset of the reaction , corresponding to a Winsor I system. The reaction mixture consists of two phases throughout the reaction. The individual phase volumes do not change as a function of conversion.…”