Volumetric Properties of Amino Alcohol-Based Protic Ionic Liquids: Influence of Counterions

Abstract

In this work, previously prepared protic ionic liquids (PILs) with 1-ammonium-2-propanol cations and five different anions, acetate, trichloroacetate, chloroacetate, 3-chloropropionate, and 4-chlorobutyrate, and their aqueous solutions were characterized. Densities of ionic liquids (ILs) and their diluted aqueous solutions have been measured over the whole composition range at selected temperatures from T = 293.15 to 353.15 K for pure ILs and from T = 293.15 to 313.15 K for diluted aqueous solutions and at atmospheric pressure (p = 0.1 MPa). The influence of specific functional groups on the anion structure, density, volumetric properties, and the nature of interactions in aqueous solutions has been discussed. Several well-known techniques and criteria, such as volumetric quantities, Hepler's coefficient, or expansibility of the ions, were used to explain water structuring and the nature of interactions in the aqueous solutions of studied PILs and classify them as the structure-making (cosmotropes) or structure-breaking (chaotropes) substances.