Aquo-DESs: Water-based binary natural deep eutectic solvents

Abstract

Deep Eutectic Solvents (DESs) are a class of solvents that are increasing their relevance in the research activity thanks to their environmental-friendly features as well as to their structural characteristics and catalytic properties. Formed by no-solvent mixing of two substances, namely a hydrogen bond donor and a hydrogen bond acceptor, DESs are finding fruitful applications in many different topics as alternatives to common organic compounds.In this work the realization, the characterization and the solubility applications of a novel water-based class of DESs are proposed. These innovative liquids, called aquo-DESs, are binary mixtures of water with glycolic acid (GA) and with trimethylglycine (TMG): GA:H2O (1:4 M ratio) and TMG:H2O (1:5 M ratio). The DES’ identity of these mixtures was demonstrated by: shifts both in terms of the molar fraction and of the melting points in the experimental melting point curves from the theoretical ones; amounts of components over their reported maximum solubility in water; thermogravimetric profiles compared to the pure substances. The aquo-DESs were characterized in their viscosity and ionic conductivity in the temperature range 20–55 °C, showing really low viscosity and low ionic conductivity, with a peculiar behavior of the ionic conductivity of GA:H2O DES. The solubilizing properties of aminoacids, phenols and carboxylic acids showed peculiar really high values whenever the solute can participate to the DES as DES component itself.