Molar enthalpy of mixing and refractive indices of choline chloride-based deep eutectic solvents with water

The molar enthalpies of mixing were measured for binary systems of choline chloride-based deep eutectic solvents (glycerol, ethylene glycol and malonic acid) with water at 298.15   K and 308.15   K, and atmospheric pressure with an isothermal calorimeter. Refractive indices were also measured at 303.15   K and atmospheric pressure. The binary mixtures of {chcl/glycerol (1:2)   +   water, chcl/ethylene glycol (1:2)   +   water} showed exothermic behaviour over the entire range of composition, while the binary mixture of {chcl/malonic acid (1:1)   +   water} showed endothermic behaviour at first and then changed to be exothermic with the increasing content of chcl/malonic acid (1:1). Experimental refractive indices were fitted with the Redlich–Kister equation, and experimental molar enthalpies of mixing were correlated with the Redlich–Kister equation and the non-random two-liquid (NRTL) model. The NRTL model with the fitted parameters was used to predict the vapour pressures of these three mixtures. For mixtures of {chcl/glycerol (1:2)   +   water} and {chcl/ethylene glycol (1:2)   +   water}, the predicted vapour pressures agreed well with the experimental results from the literature. While for mixture of {chcl/malonic acid (1:1)   +   water}, the predicted vapour pressures showed deviation at the high concentration of chcl/malonic acid (1:1), and this was probably because of the complex molecular interaction between chcl/malonic acid (1:1) and water.