Physicochemical characterization of hydrophobic type III and type V deep eutectic solvents based on carboxylic acids

Abstract

In the present work, novel type III and type V deep eutectic solvents (DESs) were prepared by mixing choline chloride (ChCl), tetrabutylammonium chloride (TBAC) or thymol as HBA, and different alkyl chain length carboxylic acids as HBD (acetic, oxalic, palmitic, stearic, oleic and linoleic acid) at various molar ratios. The hydrophobic DESs were characterized by infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR), concluding the formation of intermolecular interactions, as hydrogen bonds between the precursors. Thermogravimetric analysis (TGA) was used to obtain the thermal decomposition profiles of the prepared DESs, proving interactions between the precursors and decomposition temperatures with values, which are found in the ranges of the precursor constituents and higher than 170 °C. Other physicochemical properties, such as density, thermal expansion coefficient, dynamic viscosity, refractive index, surface tension, and thermal and ionic conductivities have been determined. Furthermore, the ability of these DESs as UV filter extractants from aqueous samples using a dispersive liquid–liquid microextraction (DLLME) previous to liquid chromatographic analysis was demonstrated. Therefore, these type III and type V DESs could be applied to the extraction of pollutants from environmental water samples.