Chapter 16 - Sorption, Lipophilicity and Partitioning Phenomena of Ionic Liquids in Environmental Systems

Abstract

This chapter focuses on ionic liquids and the phenomena of their sorption, lipophilicity, and partitioning in environmental systems. Ionic liquids consist of an organic cation—such as alkylimidazolium, alkylpyridinium, alkylphosphonium, or alkylammonium—and an organic or inorganic anion, such as tetrafluoroborate, hexafluorophosphate, tosylate, or bis(trifluoromethylsulfonyl) imide. Ionic liquids are emerging as alternative green solvents or alternative reaction media in the synthesis, catalysis, and biocatalysis reactions, and their “green” aspect derives mainly from their practically undetectable vapor pressure. Once their large-scale implementation begins, ionic liquids will soon become a permanent component of industrial effluents. Because of their great stability, they could also slip through classical treatment systems to become persistent components of the environment, where the long-term consequences of their presence are unknown. Several molecular interactions are possible between ionic liquids and the environmental compartments. The predominant sorption mechanism of ionic liquids in the soil and/or sediment matrix appears to be ion exchange. The high electron-acceptor potential of delocalized aromatic systems in the cationic compartments of ionic liquids may be responsible for electrostatic attractions with polar moieties on the particle surfaces—such as oxides, oxyhydroxides, aluminosilicates, or clay minerals—and also with the ionized carboxylic groups in humic and fulvic acids. The experimentally measured and theoretically estimated lipophilicity obtained for alkylimidazolium ionic liquids generally indicates its relatively low partitioning availability, and hence a preference for the aqueous phase.