Identifying the Thermodynamic Driving Force of Metal Extraction by Hydrophobic Eutectic Solvents

Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine

The biphasic transfer of Eu(NO)by trioctylphosphine oxide (TOPO) diluted in a molecular diluent or as a component of a hydrophobic eutectic solvent (HES) was studied by two‐phase isothermal titration calorimetry and complemented by XAS, FTIR, and NMR spectroscopy. In HES, the solvent intermolecular interactions introduce an enthalpic penalty, which is overcompensated by a reduction of the entropic cost of Eu(III) phase transfer, resulting in enhanced metal partitioning. Solvent extraction (SX) in hydrophobic eutectic solvent (HES) appears as an extension rather than a “revolution” of SX in common organic diluents for a given neutral extractant. A detailed thermodynamic and spectroscopic study shows that SX in HES imposes an enthalpic penalty but lowers the entropy cost of Eutransfer, leading to enhanced metal partitioning. graphical