How to enhance the hydrophobic nature of ionic liquids while lowering their toxicity?

Abstract

Ionic liquids (ILs) are a novel promising class of solvents with interesting physicochemical properties. Many different applications have been described as alternatives to organic solvents in chemical processes. Despite their low vapor pressure, even the water immiscible ILs shown some solubility in water that allows their dispersion into the aquatic systems resulting in water contamination. This work aims at enlarging the restricted knowledge about the ILs toxicity and inhibitory effects in aquatic ecosystems and to investigate the possibility of designing hydrophobic ionic liquids of low toxicity. In this context, biological assays were performed using organisms of different trophic levels, such as the decomposer Vibrio fischeri, the producer Pseudokirchneriella subcapitata and the first consumer Daphnia magna. This study reports a set of toxicity results, which correspond to aromatic and non-aromatic immiscible ILs, through the use of different cations (pyridinium, piperidinium, pyrrolidinium and imidazolium) and hydrophobic anions (bis(trifluoromethylsulfonyl)imide [NTf2] and hexafluorophosphate [PF6]).