Design, synthesis and properties of acidic deep eutectic solvents based on choline chloride

Four deep eutectic solvents (DESs) based on different acids as hydrogen bond donors (HBDs), namely p-toluenesulfonic acid (PTSA), trichloroacetic acid (TCA), monochloroacetic acid (MCA), and propionic acid (PA) with hydrogen bond acceptor (HBA) choline chloride (ChCl) are synthesized with a mole ratios of HBD to HBA is 2:1. The density, electrical conductivity, dynamic viscosity and refractive index of the four DESs were determined at atmospheric pressure and temperatures from (288.15 to 338.15) K at an interval of 5 K. The results show that the temperature has great influences on the physical properties of DESs. The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy were calculated by empirical equation. The molar conductivity was determined from the data of density. and conductivity. The temperature dependence of electrical conductivities and dynamic viscosities for the DESs were fitted by Vogel–Fulcher–Tamman (VFT) and Arrhenius equation. The relationship of the molar conductivity and viscosity was determined using the Walden rule. The acidities of the above DESs were measured by Hammett acidic functions. The present study will help to understand the properties of DESs and provide a guide for further applications of DESs.