Ionic Liquids as Micellar Agents in Perrhenate‐catalysed Olefin Epoxidation

Abstract

The perrhenate‐catalysed epoxidation of cyclooctene with aqueous H2O2 was performed in micellar media using imidazolium‐based ionic liquids (ILs) as surfactants. The catalytic performance of perrhenate was greatly increased in micellar media compared to IL used as neat solvent which allows for efficient use both of catalyst and IL. The choice of the surfactant alkyl chain length (C6 to C12) as well as the counterion (BF4−, TfO−, Cl−) is crucial for achieving high reaction rates. The positive effect of the addition of surfactants relies on formation of micelles. Best results are obtained for BF4− anion with long alkyl chain imidazolium cations, outperforming results for previously reported perrhenate ILs, while the use of Cl− anion leads only to similar reactivity. Cross‐over experiments revealed that the catalytically active micellar species forms in situ and that the BF4− anion promotes the reaction beyond a mere change in ionic strength. The use of Cl− anion as surfactant counterion bears potential as a novel approach for rapid screening of potentially catalytically active anions, which is exemplarily shown for tungstate anion.

Kinetics of Epoxidation of Cyclooctene with Ionic Liquids Containing Tungstate as Micellar Catalyst

“…A 1:1 mixture of the sodium salt and tungstatic acid yielded good reaction rates, low decomposition of H 2 O 2 , a selectivity of over 99 %, and complete conversion of COE after about 300 min. This in agreement with our previous results that chloride inhibits the epoxidation [14].…”

“…In our previous work [14], we have reported that sodium tungstate with [OMIM]Cl is a promising catalytic system for the epoxidation of COE using aqueous H 2 O 2 in a biphasic micellar setup. The screening was focused on the structure-reactivity relationship of the alkyl chain length at the imidazolium cation and the IL counteranion.…”

“…In a previous paper, an approach to determine the kinetics of a 1-octyl-3-methylimidazolium perrhenate [OMIM][ReO 4 ]catalyzed micellar catalysis was presented [13,14]. Therein, the micellar catalyst system was prepared by simply dissolving the Bastian Zehner As the tungstate anion is known as active species in the catalysis of epoxidation reactions, a tungstate IL micellar catalyst was prepared using the same protocol [15,16].…”

Surface-Active Ionic Liquids in Catalytic Water Splitting

“…[23,24] Several authors have demonstrated that surface-active ionic liquids led to improved reaction rates and selectivities through targeted interactions between surfactant, catalyst, and substrates. [25][26][27][28][29][30] Moreover, their ability to form carbene intermediates has a strong influence on the outcome of reactions performed in aqueous solutions of surface-active ionic liquids. [31,32] Based on recent developments in the design of N-heterocyclic carbene complexes as water oxidation catalysts with amphiphilic structures, we were interested in expanding our recent research on the application of surface-active ionic liquids in catalysis to their use in water oxidations.…”

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

“…We have recently presented a new class of imidazolium perrhenates that are active and selective epoxidation catalysts as opposed to catalytically inactive inorganic perrhenate salts such as KReO 4 . Based on our results, the activity of this type of IL catalyst relies on the formation of cationic micelles from the imidazolium moiety .…”