Empirical Polarity Parameters for Hexaalkylguanidinium-based Room-temperature Ionic Liquids

The polarity of a series of 36 hexaalkylguanidinium-based room-temperature ionic liquids (RTILs), featuring different unbranched alkyl substituents in the cation and eight different anions, has been determined by means of Reichardt's solvatochromic betaine dye; E-T(30) and the corresponding normalized E-T(N) values are presented. The positively solvatochromic probe 5-dimethylamino-5'-nitro-2,2'-bithiophene was used to characterize unspecific solvent/solute interactions (effects of dipolarity/polarizability) of ten hexaalkylguanidinium and, for comparison, two 1-alkyl-3-methylimidazolium ionic liquids.