Mechanism exploration of deep eutectic solvents extraction of indole in wash oil

Deep eutectic solvents (DESs) have gained significant interest for extracting indole from wash oil due to their exceptional characteristics and excellent extraction performance. An in-depth comprehension of the intermolecular interactions within the DES-wash oil system is crucial for developing principles that can guide the design of highly efficient DESs for indole extraction. The intermolecular interactions, molecular associations, and density profile in the DES-wash oil system were investigated using molecular dynamics simulation and FT-IR/1H NMR characterization. The DES was composed of tetraethylammonium chloride and glycerol (TEAC/GLY), which was selected based on its exceptional experimental performance. Both the simulation and spectra results show that indole has strong hydrogen bond with TEAC/GLY. The hydrogen bond promotes indole extraction while van der Waals interactions cause aromatics entrainment. The components in wash oil exhibit two distinct molecular associations before and after the extraction of indole. A well-defined interface is established between the wash oil molecules and DES components, and indole has a preference for accumulating at the interface. The results provide an insight into the mechanism of extracting indole from wash oil using DES.