Insights into the Synthesis and Properties of Deep Eutectic Solvents Based on Cholinium Chloride and Carboxylic Acids

Abstract

Recently, many studies concerning the environmental impact of ionic liquids (ILs) have shown that despite their unique properties and clear advantages in an ever wide range of applications and processes, ILs are not intrinsically green. In a search for biodegradable and low toxicity, a new type of ILs has been developed, the deep eutectic solvents (DESs). In this context, the aim of this work is to provide accurate densities, viscosities, and refractive indices for DESs prepared using cholinium chloride as the hydrogen bond acceptor and several carboxylic acids (levulinic, glutaric, malonic, oxalic, and glycolic) as the hydrogen bond donors. The impact of two different synthetic methodologies, heating and grinding, in the thermophysical properties of the prepared DESs was assessed. The obtained DESs were analyzed using NMR spectroscopy, FTIR, and electrospray ionization mass spectrometry in order to check their structures and purities. Thermophysical properties, densities, viscosities, and refractive indices were rationalized in terms of the chemical structure of the prepared DESs. The effect of the presence of water in the thermophysical properties of the compounds was also evaluated. Finally, comparisons between the DESs and the corresponding ILs are presented.