Insights into the formation mechanism of aliphatic acid-choline chloride deep eutectic solvents by theoretical and experimental research

Deep eutectic solvents (DESs) are considered as "green solvents". In this work, seven aliphatic acid-choline chloride DESs (AA-ChCl DESs) were successfully prepared. With the help of density functional theory (DFT) calculations, the experimental peaks that cannot be directly or accurately confirmed have been identified. The formation mechanism was studied with Fourier transform infrared (FT-IR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy and DFT calculation. The liquid formation of the AA-ChCl DESs mainly depends on two forces, the hydrogen bonds of OH···Cl and OH···O. Among them, the OH···Cl play a leading role. The OH···Cl interaction strength decreased with the alkyl chain of aliphatic acids due to the increase of intermolecular distance, which means that the formation ability of AA-ChCl decreased gradually. It hopes that the current work can provide useful information to design DESs and expand their potential applications.