A comprehensive study of the water stability of eutectic solvents using COSMO-SAC

Abstract

The water stability of deep eutectic solvents (DESs) is an important factor because the preferential interaction with water of one or both DESs precursors may change the nature of the solvent and impact its performance. In this work, Conductor-like Screening Model-Segment Activity Coefficient (COSMO-SAC) was applied to investigate the stability of both hydrophilic and hydrophobic eutectic solvents (ESs) in the presence of water. With this objective, an initial computational evaluation of all possible combinations of ES composed by twenty-two different hydrogen bond acceptors (HBA) and forty-four hydrogen bond donors (HBD) at three different molar ratios of HBA: HBD (2:1, 1:1, and 1:2) was carried. The results revealed that the hydrophobic ESs based on tetraalkyl -ammonium salts, terpenes and fatty acids as HBA and fatty alcohols and fatty acids as HBD are the DESs with higher water stability. Therefore, four different groups of eutectic solvents, namely menthol: fatty alcohol, menthol: fatty acid, fatty acid: fatty acid and fatty acid: fatty alcohols were selected to evaluate the COSMO-SAC predictions using water activity measurements. It is shown that a good agreement was obtained between the calculated and the experimental results and that the hydrophobicity of the eutectic solvents controls its water stability. A thermophysical characterization of the eutectic solvents studied is also reported.