A Hydronium Solvate Ionic Liquid: Facile Synthesis of Air-Stable Ionic Liquid with Strong Brønsted Acidity

Abstract

© The Author(s) 2018. A new kind of ionic liquid (IL) with strong Brønsted acidity, i.e., a hydronium (H 3 O + ) solvate ionic liquid, is reported. The IL can be described as [H 3 O + · 18C6]Tf 2 N, where water exists as the H 3 O + ion solvated by 18-crown-6-ether (18C6), of which the counter anion is bis(trifluoromethylsulfonyl)amide (Tf 2 N – ; Tf = CF 3 SO 2 ). The hydrophobic Tf 2 N– anion makes [H 3 O + · 18C6]Tf 2 N stable in air. The Hammett acidity function (H 0 = −4.4) of molten [H 3 O + · 18C6]Tf 2 N, evaluated using the indicator method, is a new record for ILs and indicates strong aciditiy. The findings regarding this proton-condensed solvate IL are of fundamental interest, and will help in the design of media for new acid-base reactions.