No abstract

A systematic investigation of influence of the length of the side alkyl chain and the counter ions on the thermodynamic of the micellization process at imidazolium based surface active ionic liquids (SAILs) in aqueous solution was carried out by isothermal titration calorimetry (ITC) in a broad temperature range. The effect of alkyl chain length on the micellization process in water has been investigated on 1decyl-3-methylimidazolium ([C 10 mim]Cl) 1-dodecyl-3-methylimidazolium ([C 12 mim]Cl), 1tetradecyl-3-methylimidazolium ([C 14 mim]Cl) and 1-hexadecyl-3-methylimidazolium ([C 16 mim]Cl) chlorides, whereas the influence of counterion was studied at the micellization of 1-dodecyl-3-methylimidazolium chloride ([C 12 mim]Cl), bromide ([C 12 mim]Br), iodide ([C 12 mim]I), acetate ([C 12 mim]OAc), methanesulfonate ([C 12 mim]OMs), toluensulfonate (([C 12 mim]OTs), trifluromethane sulfonate ([C 12 mim]OTf), trifluoro acetate (([C 12 mim]TFA) and salicylate ([C 12 mim]Sal) in water.

A series of surface-active ionic liquids based on the 1-dodecyl-3-methylimidazolium cation and different anions was synthesized and applied for micellar catalysis of nucleophilic substitutions.

Surface-active ionic liquids based on imidazolium cations are promising targets for micellar catalysis in aqueous solution, yielding enhanced rate constants compared to surfactants based on n-alkyltrimethylammonium cations and exhibiting a pronounced counterion dependence ( Bica Chem. Commun. 2012 , 48 , 5013 - 5015 ; Cognigni Phys. Chem. Chem. Phys. 2016 , 18 , 13375 - 13384 ). Probably most relevant to these effects is the interplay between headgroup hydration and counterion binding. To obtain more detailed information on these effects, aqueous solutions of 1-dodecyl-3-methylimidazolium ([CMIM]) bromide, iodide, and triflate (TfO) were investigated at 45 °C using broadband dielectric spectroscopy, viscosity measurements, and small-angle X-ray scattering experiments. Effective hydration numbers were determined, and information on the locations and mobilities of the condensed counterions, X, was derived. It was found that [CMIM] halide micelles were less hydrated than the corresponding n-dodecyltrimethylammonium ([CTA]X) aggregates. Together with their somewhat weaker counterion condensation, this difference probably explains their higher catalytic activity. Whereas [CMIM]Br micelles remained roughly spherical in the studied concentration range, rodlike aggregates were formed at high concentrations of the iodide and, in particular, the triflate surfactants. It appears that the much lower mobility of condensed TfO counterions is the reason for the very low catalytic activity of [CMIM]TfO micelles.

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.