Recently, deep eutectic solvents (DESs) have been introduced as new types of green solvents due to their environmentally friendly, non-toxicity, and favorable physicochemical properties over conventional organic solvents. Therefore, studying their physical properties will provide great help to design processes in the application fields. In this work, four new DESs are successfully prepared by using benzilic acid (BA) as hydrogen bond donor (HBD) with choline chloride (ChCl), tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPAB), and tetrabutylammonium hydrogen sulfate (TBAHS) as hydrogen bond acceptors. The physicochemical properties of the DESs such as density, speed of sound, conductivity, viscosity, refractive index, and surface tension measured as a function of temperature. The melting temperatures of the DESs have been measured by using the Differential Scanning Calorimetry (DSC) method and the 1H, 13C NMR, and Fourier transforms infrared (FTIR) analysis carried out to confirm their chemical structure, purities, and occurrence interaction between the investigated HBAs and HBD which formed the deep eutectic mixtures.
