Low‐Melting, Low‐Viscous, Hydrophobic Ionic Liquids: 1‐Alkyl(Alkyl Ether)‐3‐methylimidazolium Perfluoroalkyltrifluoroborate

Abstract

A series of twenty two hydrophobic ionic liquids, 1-alkyl(alkyl ether)-3-methylimidazolium ([C_mmim]⁺ or [C_mO_nmim]⁺; where C_m is 1-alkyl, C_m=nC_mH_2m+1, m=1–4 and 6; C_mO_n is 1-alkyl ether, C₂O₁=CH₃OCH₂, C₃O₁=CH₃OCH₂CH₂, and C₅O₂=CH₃(OCH₂CH₂)₂) perfluoroalkyltrifluoroborate ([R_FBF₃]⁻, R_F=CF₃, C₂F₅, nC₃F₇, nC₄F₉), have been prepared and characterized. Some of the important physicochemical properties of these salts including melting point, glass transition, viscosity, density, ionic conductivity, thermal and electrochemical stability, have been determined and were compared with those of the reported [BF₄]⁻-based ones. The influence of the structure variation in the imidazolium cation and the perfluoroalkyltrifluoroborate ([R_FBF₃]⁻) anion on the above physicochemical properties was discussed. The key features of these new salts are their low melting points (−42 to 35 °C) or extremely low glass transition (between −87 and −117 °C) without melting, and considerably low viscosities (26–77 cP at 25 °C).