Formation of Deep Eutectic Solvents by Phenols and Choline Chloride and Their Physical Properties

Abstract

Novel deep eutectic solvents (DES) based on three different hydrogen-bond donors (HBD), namely phenol, o-cresol, and 2,3-xylenol, and choline chloride (ChCl) were successfully synthesized with different mole ratios of HBD to ChCl. Melting temperature of these DES were measured. Compared with an ideal mixture of the two components, the freezing temperature of the DES depresses greatly from (120 to 127) K. The physical properties, such as density, viscosity, and conductivity of phenol-based and o-cresol-based DES were determined at atmospheric pressure and temperatures from (293.2 to 318.2) K at an interval of 5 K. The results show that the type of HBD, the mole ratio of HBD to ChCl, and temperature have great influences on the physical properties of DES. Densities and viscosities of DES formed by phenol and ChCl decrease with increases of temperature and phenol content. The conductivities of the DES are from (1.40 to 7.06) mS·cm–1, similar to that of room temperature ionic liquids. The conductivities of the DES increase with an increase of temperature, and reach the highest values at phenol to ChCl mole ratios of 4.00 to 5.00. The temperature dependence of densities and conductivities for these DES were correlated by an empirical second-order polynomial with relative deviations less than 0.91 %, and the viscosities were fitted to the VTF equation with relative deviations less than 0.52 %.

Room-Temperature Molten Salts: Protic Ionic Liquids and Deep Eutectic Solvents as Media for Electrochemical Application

“…At 25 °C, the viscosity values of different DESs reported in the literature range from 50 mPa s to 5,000 mPa, for example, viscosity up to 500 mPa · s is reported in the case of the equimolar oxalic acid/choline chloride DES system [23,81,82]. In general, at 25 °C the DES viscosity values are similar to those observed in the case of classical ILs.…”

Novel manganese(II)-based deep eutectic solvents: Synthesis and physical properties analysis

“…As the covalent bonds were formed, the crystal structure of MnCl 2 Á4H 2 O with acetamide or glycerol collapsed and this could leads towards the lower lattice energies in the DESs [27]. Where in such case, lesser energy is required to break the bonds, resulting in a depression of freezing point when the ion size is larger with smaller ion charges [28].…”

“…Where in such case, lesser energy is required to break the bonds, resulting in a depression of freezing point when the ion size is larger with smaller ion charges [28]. Thus, such DES with low lattice energy is the reason for its liquid phase existence at room temperature [27]. These findings are especially interesting as generally, DESs with a freezing point lower than 50 8C are of special demand since they could be at lower cost of production and usage, also as safer solvents in many industries [29].…”

“…Viscosity reflects the interaction between molecules in a liquid mixture [27]. As refer to Table 1, DES1 with acetamide as HBD has the lowest viscosity value.…”

The new liquid–liquid extraction method for separation of phenolic compounds from coal tar

“…Pang et al [26] found that choline chloride can react with phenols to form DES, which become a uniform liquid phase to separate phenols from oil. Guo et al [27,28] studied the phenol removal efficiency of choline chloride and its homologous compounds from model oils and then discussed how different cations and anions affect the removal efficiency of phenol. With the upsurge of green chemistry, the utilization of DES is predicted to draw increasing attention.…”