Tuning the hydrophobicity-hydrophilicity: D,L-Menthol:Dodecanoic acid (2:1) in glycols – n-Hexane biphasic systems

Abstract

Hydrophobic molecular eutectic solvents have been largely explored in the last decade especially due to the high tunability of their properties, according to the nature of their components and their proportions. Their use together with conventional solvents, such as water to develop hydrophobic-hydrophilic biphasic system is growing at a fast pace. This work explores the use of glycols to separate binary mixtures composed of two hydrophobic miscible components: a conventional solvent and neutral hydrophobic eutectic solvent (ES). For that purpose, D,L-menthol:dodecanoic acid (2:1), and n-hexane were used, adding low-molecular weight glycols, ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and 200, 400 g/mol polyethylene glycol (PEG 200 and PEG 400 respectively) to promote phase splitting. As glycol molecular weight grows from EG to PEG 400, its hydrophobicity increases, and thus dodecanoic acid (C12) greatly changes its partition preferences, from n-hexane rich phase to an evener distribution between both phases, while D,L-menthol has the highest affinity for the hexane-rich phase. Finally, these two phases hydrophobic systems were used, as a proof of concept, in the separation of carotenoids from chlorophyll, where the easy tunability of the phases just by altering the ratio between the ES components is demonstrated, directing the components from one phase to the other.