Physicochemical properties of choline chloride-based deep eutectic solvents with polyols: an experimental and theoretical investigation

Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, solvents should meet a few important standards such as availability, nontoxicity, biodegradability, recyclability, flammability, and low price among others. Deep eutectic solvents (DESs) are the type of solvents that can meet these conditions. In this work, we performed experimental and computational studies on the DESs, type III group, which are mixtures of xylitol and sorbitol with choline chloride at eutectic composition. The mentioned DESs were compared with commonly used DESs of sugar alcohols: Ethylene glycol and glycerol. Moreover, the key factor for choosing these solvents is that their freezing points are below 293.15 K, and so, they are all liquids at room temperature. With the growing interest in this field, there is an urgent need for a deep understanding on the formation and functioning of these solvents at the molecular level. Besides, complementarity of theoretical and experimental studies can be helpful in further designing novel DESs. Thus, in this work, we report the physicochemical properties of the mentioned DESs, which include density, viscosity, electrical conductivity, molar volume, refractive index, molar refraction, and free molar volume in temperatures ranging from 293.15 to 353.15 K. The reported properties were fitted to appropriate linear or polynomial equations with very satisfactory correlation coefficients (R2). Moreover, the density functional theory (DFT) method and molecular dynamics (MD) simulations have been used to probe DESs at the molecular level. Molecular dynamic simulations confirmed that hydrogen bonds between sorbitol, xylitol, and choline chloride play a fundamental role in the observed properties of these DESs.