Solvatochromic parameters of imidazolium-, hydroxyammonium-, pyridinium- and phosphonium-based room temperature ionic liquids

Abstract

Solvatochromic solvent parameters of different room temperature ionic liquids based on the imidazolium, hydroxyammonium, pyridinium and phosphonium cations, namely 1-butyl-3-methyl imidazolium hexafluorophosphate, 1-hexyl-3-methyl imidazolium hexafluorophosphate, 1-octyl-3-methyl imidazolium hexafluorophosphate, 1-octyl-3-methyl imidazolium tetrafluoroborate, N-octylpyridinium tetrafluoroborate, 2-hydroxyethylammonium formate, 2-hydroxypropylammonium formate, trihexyl-(tetradecyl)phosphonium chloride, trihexyl-(tetradecyl)phosphonium bromide, trihexyl-(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide and trihexyl-(tetradecyl)phosphonium dicyanamide were determined at 25 °C using UV-Vis spectroscopy. Specifically, we have measured the Kamlet-Taft parameters: α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), π∗(dipolarity/polarizability) and the Reichardt's normalized polarity parameter, ET N. In previous works, we employed the Solvation Parameter Model to predict the partition coefficients for compounds of biological and pharmacological interest and to elucidate the chemical interactions involved in the partition process of different probe molecules between water and different types of ionic liquids. In this work, we have used the obtained solvatochromic solvent parameters to explain and understand the relative magnitudes of the chemical interactions obtained with the solvation parameter model.