Solvatochromic Behavior of Polarity Indicators in PILs and Their Mixtures with Molecular Solvents: Autoprotolysis and Its Relation to Acidity

Abstract

: It is interesting to know the behavior of Protic Ionic Liquids (PILs) within the binary mixture of molecular solvents since it is usual to carry out processes such as organic and inorganic synthesis, or liquid-liquid extractions in the presence of another solvent. Moreover, on certain occasions the absence of water is strictly required. In this sense, it is important to note that the addition of small amounts of IL to the molecular solvent allows a fine adjustment in its microscopic properties; obtaining “ new solvent systems ” with particular properties. Taking into account that solvatochromic indicators are traditionally used as microscopic descriptors to determine the molecular microscopic properties of solvents. In this sense, we look for re-evaluate the behavior of solvatochromic probes and reconsider the validity of traditional polarity scales such as ET(30), in alkylammonium-based PILs and in their mixtures with molecular solvents, taking into account now that the real composition of these PILs depends on the equilibrium of autoprotolysis. In addition to the spectroscopic analysis developed, the characterization of the PILs and their binary mixtures was completed in terms of a ch ange in the ∆pKa of the precursor species of a PIL. Thermal analysis was also employed to determine the acid strength ’ s role in ions complete formation in pure PILs.