Novel hydrophobic ionic liquids based on quaternary ammonium and perfluoroalkyltrifluoroborate

Abstract

A novel class of low-melting, hydrophobic ionic liquids based on relatively small aliphatic quaternary ammonium cations ([R1R2R 3NR]+, wherein R1, R2, R3 = CH3 or C2H5, R = n-C3H 7, n-C4H9, CH2CH2OCH 3) and perfluoroalkyltrifluoroborate anions ([RFBF 3]-, RF = CF3, C2F5, n-C3F7, n-G4F9) have been prepared and characterized. The important physicochemical and electrochemical properties of these salts including melting point, glass transition, viscosity, ionic conductivity, and electrochemical stability, have been determined and comparatively studied with those of the corresponding [BF4] -- and [(CF3SO2)2N] --based ones. The influence of the structure variation in the quaternary ammonium cation and perfluoroalkyltrifluoroborate ([R FBF3]-) anion on the above physicochemical properties is discussed. Most of these salts are liquids at 25°C and exhibit low viscosities (58-210 cP at 25°C) and moderate conductivities (1.1-3.8 mS cm-1). The electrochemical windows of these salts are much larger than those of the corresponding 1,3-dialkyimidazolium salts. Additionally, a number of the salts with [RFBF3]- show plastic crystal behavior.