Physical Properties of Alcohol Based Deep Eutectic Solvents.

The physical properties, viscosity, conductivity, surface tension and density were measured for a series of alcohol based Deep Eutectic Solvents (DES) as a function of choline chloride (ChCl) concentration. The point at which the system becomes a saturated salt solution in the diol systems is at 20 mol% ChCl, because at higher concentrations the conductivity decreases despite the increase in number of charge carrying species. The addition of ChCl to glycerol results in a decrease in the viscosity of the system by interrupting the intermolecular hydrogen bonding of the glycerol molecules, whereas the addition of ChCl to the diols results in an increase in viscosity. The mono-alcohol phenol has been shown to form a DES in a ratio of 4:1 phenol: ChCl. Stable DES’s have also been formed using sugars, D-(-) fructose, D-glucose, xylitol and meso-erythritol. Determination of solvent-solute interactions is key to the understanding of solvent properties in liquids therefore the Kamlet-Taft parameters α, β, π* and ET (30) parameter were determined for a series of alcohol based DES using three solvatochromic dyes, 4-nitroaniline, N,N-dimethyl-4-nitroaniline and Reichardt’s dye ET (30). It is shown that they are similar to RNH3+X-, R2NH2+X- and imidazolium ionic liquids. The effect of ChCl on the Kamlet-Taft parameters is not uniform across the systems and is dependant upon the hydrogen bond donor. The solventless esterification of glycerol and lauric was carried out using ChCl with the intention of using its hydrogen bonding interaction with glycerol to behave a potential site inhibitor as to selectively form mono- or di-ester products. The work has shown that the addition of ChCl to the system, initially slows the rate of the mono-ester formation, but actually encourages the reaction to progress further towards the di-ester product, when compared to the pure glycerol system encouraging only mono-ester formation.