Physicochemical properties and toxicities of hydrophobic piperidinium and pyrrolidinium ionic liquids

Some properties are reported for hydrophobic ionic liquids (IL) containing 1-methyl-1-propyl pyrrolidinium [MPPyrro]⁺, 1-methyl-1-butyl pyrrolidinium [MBPyrro]⁺, 1-methyl-1-propyl piperidinium [MPPip]⁺, 1-methyl-1-butyl piperidinium [MBPip]⁺, 1-methyl-1-octyl pyrrolidinium [MOPyrro]⁺ and 1-methyl-1-octyl piperidinium [MOPip]⁺ cations. These liquids provide new alternatives to pyridinium and imidazolium ILs. High thermal stability of an ionic liquid increases safety in applications like rechargeable lithium-ion batteries and other electrochemical devices. Thermal properties, ionic conductivities, viscosities, and mutual solubilities with water are reported. In addition, toxicities of selected ionic liquids have been measured using a human cancer cell line. The ILs studied here are sparingly soluble in water but hygroscopic. We show some structure-property relationships that may help to design green solvents for specific applications. While ionic liquids are claimed to be environmentally benign solvents, as yet few data have been published to support these claims.