Choline Chloride- and Organic Acids-Based Deep Eutectic Solvents: Exploring Chemical and Thermophysical Properties

Abstract

Deep eutectic solvents (DES) have been the subject of numerous studies in the literature with the aim of replacing traditional solvents due to their green solvents' characteristics such as low toxicity, biodegradability, and versatility. Despite their numerous advantages, it is increasingly urgent to determine their chemical and thermophysical properties for a more accurate industrial use. This study presents experimental data on the physicochemical properties of deep eutectic solvents containing choline and different organic acids. Spectroscopy analyses confirm the occurrence of carboxylic esterification reaction, particularly in the malonic acid mixture. Thermal analyses by differential scanning calorimetry and thermogravimetric analysis reveal the crucial role of hydrogen bond donors in the thermophysical characteristics of the DES prepared. The thermophysical behaviors of DES are described by linear relationships, where the size of the alkyl chain exerts a considerable influence on the parameters of density, viscosity, and refractive index. Cyclic voltammetry demonstrates a wide electrochemical stability window (−1.16 to 2.19 V) for mixtures containing malonic and 3-phenylpropionic acids and a pronounced irreversible reductive signal for mixtures containing acetic and propionic acids.