Hydrophobic Ionic Liquids Composed of Perfluoroalkyltrifluoroborates for Ionic Liquid-Water Two-Phase Systems

Ionic liquids (ILs) composed of perfluoroalkyltrifluoroborate ions (CnF2n+1BF3-, n = 2, 3, 4, and 6) and highly hydrophobic cations are found to have properties suitable to the applications of ILs in IL-water (W) two-phase systems because of their high stability against hydrolysis, high hydrophobicity, and low melting points. The rate of hydrolysis of CnF2n+1BF3- is four orders of magnitude slower than that of BF4-. The ion-transfer voltammograms for the transfer of CnF2n+1BF3- across the interface between nitrobenzene and W show that these CnF2n+1BF3- have hydrophobicity comparable to or higher than those of PF6- and bis(trifluoromethylsulfonyl)imide depending on n. The physicochemical properties (density, viscosity, conductivity, and solubility of ILs in W) of CnF2n+1BF3--based ILs are measured for the ILs having melting points lower than room temperature. The hydrophobicity of the CnF(2n+1)BF(3)(-) ions is Well Correlated with the solubility of the ILs in W and also with the width of the polarized potential window at the IL/W interface.