Surface-active ionic liquids in catalysis: Impact of structure and concentration on the aerobic oxidation of octanol in water

Abstract

We present design and synthesis of surface-active ionic liquids for the application in micellar catalysis. A series of 1-methyl-3-dodecylimidazolium based ionic liquids with variable core structures including dicationic and zwitterionic ones was synthesized and characterized. These surface-active ionic liquids where applied in the aerobic oxidation of aliphatic alcohols to carbonyl compounds. A strong dependence on the ionic liquid concentration and structure was identified, which is in accordance with the concepts of micellar catalysis. Optimum conditions for the oxidation of 1-octanol could be identified, and the use of surface-active ionic liquids strongly improved the reaction performance compared to pure water. Under optimized conditions, it was possible to isolate up to 75% of octanoic acid using only small amounts of surface-active ionic liquid in a 0.05mM solution in water without further ligands.

Surface-Active Ionic Liquids in Catalytic Water Splitting

“…Based on our previous experience in the field of micellar catalysis with surface-active ionic liquids, we selected three surface-active 1-dodecyl-3-alkyl-imidazolium-based ionic liquids 2a-4a, including a dicationic species, for simultaneous use as ligand and surfactant in the water oxidation reaction. [26,31] For the purpose of comparison, dimethylimidazolium bromide, which does not possess any surface-active behaviour, was also included as it has already been used as a precursor for iridiumbased water oxidation catalysts. Starting with the structures shown in Fig.…”

“…[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. Here, we present the use of surface-active imidazolium-based ionic liquids as ligands and reaction media for iridium-catalyzed water oxidations, envisioning that their ability to form aggregates in water should also facilitate the formation of the catalyst dimer assumed to be a key step in the oxygen-oxygen bond formation.…”

1-Octyl-3-(3-(1-methylpyrrolidiniumyl)propyl)imidazolium Bis(trifluoromethane)sulfonimide

“…Because of these features, dicationic ILs (DILs) have been shown to possess superior tunability potential when compared to monocationic ILs, and this advantage has been exploited for designing DILs for specific applications; for example, DILs exhibited much higher thermal degradation temperatures [18,19], wider liquid ranges, higher densities, higher glass transition temperatures and melting points, larger surface tensions, higher shear viscosities [20], and electrochemical windows in the range of 4.3 V to 4.7 V [21]. These properties offer a wider portfolio of possible applications, such as their use as stationary phases for gas chromatography capillary columns [22], high temperature lubricants, and solvents and catalysts in high-temperature reactions [23][24][25][26]. Besides, the electrochemical properties make them attractive as electrolytes in high-temperature batteries [27,28] and in dye-sensitized solar cells [29].…”

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

“…In recent years, several applications of ionic liquids (ILs) as micellar catalysts have been developed [23][24][25][26]. However, their application as micellar epoxidation catalyst has not yet been reported.…”