Interfacial Behavior of Cs ⁺, K ⁺, Na ⁺, and Rb ⁺ Extraction in the Presence of Dibenzo-18-Crown-6 from the Nitrobenzene–Water Biphasic System: Experimental, Quantum Chemical, and Molecular Dynamic Studies

Abstract

Extraction of metal ions (i.e., Cs ⁺, K ⁺, Na ⁺, and Rb ⁺) in the presence of ionophore such as dibenzo-18-crown-6 (DB18C6) from the nitrobenzene–water biphasic system is reported by COSMO-RS (conductor-like screening model for real solvents) predictions, molecular dynamics simulation, along with experimental validation. The predicted values of selectivity as obtained for the Na ⁺–DB18C6 complex were 4.571, 4.877, and 4.947 at 298.15, 308.15, and 318.15 K, respectively. This was then confirmed by the experimental distribution coefficient ( D) as obtained in the diluent systems along with by varying the metal ion to crown ether ligand (M–L) mole ratios: 10:1 (0.1 M M ⁺ and 0.01 M DB18C6), 1:1 (0.01 M M ⁺ and 0.01 M DB18C6), and 1:10 (0.001 M M ⁺ and 0.01 M DB18C6). The experimentally determined values of D _Na (i.e., 0.059, 0.060, and 0.056) were found to be very large as compared to the values of D _Cs (i.e., 0.001, 0.010, and 0.024) in the nitrobenzene phase. It indicates an excellent extraction ability of DB18C6 for Na ⁺. The rate of phase separation for the Cs ⁺NO ₃ ^– system was slow as compared to other metal ion systems. The binding energies, free energies, and nonbonded interaction energies of the complexed metal ion in solution were calculated with both explicit and implicit solvent models. A higher interaction energy between Na ⁺–DB18C6 complex and nitrobenzene was observed (i.e., −289.92 in the explicit model and −143.12 kcal/mol in the implicit model) when compared with other metal ions (i.e., Cs ⁺, K ⁺, and Rb ⁺).