Experimental Measurements of Octanol-Water Partition Coefficients of Ionic Liquids

Montalbán MG, Collado-González M, Trigo R, Díaz Baños FG and Víllora G

Interest in ionic liquids (ILs) has increased due to their promising use as “green solvents” because of their negligible vapor pressure. However, their solubility in water could lead to their dispersion into the environment through liquid effluents, generating an important toxicological effect in soils and seawater. One of the most relevant parameters related to the assessment of environmental risk is the octanol-water partition coefficient (Kow). With this parameter is possible to estimate some ecosystem risk factors such as bioaccumulation, sorption to soils and sediments and toxicity in fish by the usage of experimental correlations. Shake-flask and slow-stirring methods are the most currently used methods for determining the Kow of a chemical compound. The former has the disadvantage that equilibrium might not be reached quickly, while the slow-stirring method is not always suitable for ILs, since some of them may decompose after continuous contact with water. We have developed a combined version of both methods. Here, we present measurements of the Kow of twenty-four ILs at 30°C, using the three experimental methods. The types of anion and alkyl chain length of the cation are among the parameters studied. The Kow of ILs used in this study range between 0.0017 and 3.6567 at 30°C. The Kow of ILs studied is lower than in commonly used industrial solvents.