1-n-Butyl-3-methylimidazolium ([bmim]) octylsulfate—an even ‘greener’ ionic liquid

Abstract

Ionic liquids are considered as green solvents mainly due to their lack of vapour pressure. In fact, environmental and safety problems arising through the volatility of organic solvents can be avoided by the use of these innovative liquids. However, typical ionic liquids consist of halogen containing anions (such as [AlCl₄]⁻, [PF₆]⁻, [BF₄]⁻, [CF₃SO₃]⁻ or [(CF₃SO₂)₂N]⁻) which in some regard limit their ‘greenness’. The presence of halogen atoms may cause serious concerns if the hydrolysis stability of the anion is poor (e.g. for [AlCl₄]⁻ and [PF₆]⁻) or if a thermal treatment of spent ionic liquids is desired. In both cases additional effort is needed to avoid the liberation of toxic and corrosive HF or HCl into the environment. In this context, we present here the synthesis and application of 1-n-butyl-3-methylimidazolium ([bmim]) [n-C₈H₁₇OSO₃] which represents a halogen-free and relatively hydrolysis-stable ionic liquid. Moreover, the technical availability and the well documented toxicology of the octylsulfate anion make this ionic liquid a highly interesting candidate for industrial application.