An improved preparation of ionic liquids by ultrasound

The use of ionic liquids (ILs) as a novel class of environmentally friendly solvents is now of topical interest among the chemical community, worried about the environmental impact of chemicals. Many reactions of organic chemistry have thus been re-examined since the 1990s. Nevertheless, even if a given preparation of ILs does not represent any particular difficulty, the reaction times appear to be long and the use of large amounts of classical solvents for the synthesis and the purification steps is crucial. This article presents preliminary work performed for the ultrasound assisted preparation of several 1-butyl-3-methylimidazolium salts (BF₄, PF₆, CF₃SO₃ and BPh₄). In all cases a clear yield increase results and a dramatic reduction of the reaction time accompanied by an improved quality of the products occurs. After a short and simple work-up, the ILs are ready to use without a further purification step. Moreover, an original and simple analytical way to follow the reaction in real time is also presented.