Synthesis of [EMIM]OH via bipolar membrane electrodialysis – precursor production for the combinatorial synthesis of [EMIM]-based ionic liquids

Abstract

A new environmentally benign process for the production of aqueous solutions of [EMIM]OH is reported. Electrodialysis with bipolar membranes (EDBM) was implemented for the first time to produce this hydroxide-based precursor in 5% concentration in water from the non-toxic bulk ionic liquid [EMIM][EtOSO₃] at the kg-scale. The results are discussed with regard to ease of operation, productivity and obtained product quality. Moreover, several structurally new ionic liquids were synthesized by reaction of the aqueous precursor solution with different acids, such as, e.g., H₂SiF₆ or hexafluoroacetylacetone. But also the synthesis of well-established ionic liquids, such as, e.g., [EMIM][BF₄] has been carried out using the hydroxide intermediate and the full procedure is compared to well-established ion metathesis protocols.