Thermodynamic study of crown ether-lithium/magnesium complexes based on benz-1,4-dioxane and its homologues

Abstract

The synthesis and characterization of benz-1,4-dioxane crown ethers (CEs) and some of its homologues are described and analyzed. The effect of added C-atom within the CE ring (increasing the hydrophobicity of the CE ring by increasing the number of CH2-units) on the Li+ and Mg2+ complexation within a liquid–liquid extraction (LLE) is investigated and thermodynamically analyzed. The complex stability constant K, the change of entropy ∆S and enthalpy ∆H, and the Gibbs free energy ∆G are determined. The enhanced hydrophobicity of the CE ring results in stronger complexation stability of the Mg2+ complex, while the Li+ complexes are less favored. This effect mainly occurs due to the increased entropy term with improved hydrophobicity of the CE. These results indicate a stronger extraction of Li+ in Mg2+ -containing aqueous resources if more hydrophilic CEs are used.