Sudhir N. V. K. Aki

Octanol-water partition coefficients of imidazolium-based ionic liquids

Ionic liquids (ILs) are low melting organic salts that are being vigorously investigated as possible replacements for volatile organic solvents. While they cannot contribute to air pollution due to their negligible vapor pressure, they do have significant solubility in water. As a result, this is the most likely medium through which ILs will enter the environment. Therefore, it is important to understand how ILs will influence aquatic ecosystems. A simple thermodynamic measurement that has been extremely useful in estimating effects of chemical pollutants on aquatic environments is the octanol–water partition coefficient (KOW). It is an extremely important quantity because it describes the hydrophobicity or hydrophilicity of a compound and has been correlated with bioaccumulation and toxicity in fish, as well as sorption to soils and sediments. Here we present measurements of the KOW of twelve imidazolium-based ILs at room temperature, using the slow-stirring method. For the butylmethylimidazolium cation, KOW values range from 0.003 to 11.1, depending on the choice of anion. In addition, we find that the KOW values increase with increasing alkyl chain length on the cation and that replacing the acidic hydrogen on the carbon between the two nitrogens in the imidazolium ring with a methyl group has negligible effect on the KOW. However, all of the KOW values measured, even for the most “hydrophobic” imidazolium-based ILs, are less than 15 so these ILs will not accumulate or concentrate in the environment.

How polar are room-temperature ionic liquids?

The solvent strength and polarity of four imidazolium and pyridinium based ionic liquids, as measured using two different fluorescent probes, indicate that these liquids are more polar than acetonitrile but less polar than methanol.

Carbon dioxide induced separation of ionic liquids and water

Both hydrophobic and hydrophilic room-temperature ionic liquids can be separated from aqueous solutions with relatively low-pressure gaseous carbon dioxide.

Enhancement of oxygen and methane solubility in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide using carbon dioxide

The presence of CO(2) increases the solubility of O(2) and CH(4) in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide at 25 degrees C and pressures to 13 bar.

Removal of ammonium bromide, ammonium chloride, and zinc acetate from ionic liquid/organic mixtures using carbon dioxide

Carbon dioxide can be used to remove ammonium salts and zinc acetate from ionic liquid/organic mixtures at 25 °C. The amount of CO2 required to achieve this separation is minimal.