Toward a Critical Evaluation of DES-Based Organic Biphasic Systems: Are Deep Eutectic Solvents so Critical?

Six biphasic systems containing heptane, ethanol, and either hydrogen bond donor compounds (HBD), glycerol, ethylene glycol, levulinic acid, or the corresponding choline chloride-based DES were studied as potential extracting systems for five natural compounds, namely, quercetin, apigenin, coumarin, β-ionone, and α-tocopherol. Phase diagrams for all biphasic systems are reported. It appears that the polarity of the HBD is the most relevant property driving the phase separation and that choline chloride has only a minor influence on the phase diagram. Measurements of the partition coefficients for the five natural compounds mentioned above reveal that the influence of choline chloride on the partition coefficient of a natural compound is only significant when the latter is present in both phases. Finally, binodal curves and partition coefficients were calculated using a conductor-like screening model for real solvents (COSMO-RS). Calculated and experimental results are in good agreement, confirming that COSMO-RS is a useful and promising tool for screening such complex biphasic systems to find the most adequate system for purifying specific natural compounds.