Dehydration of a polyether type extraction agent and of the corresponding K+ complex: insights into liquid-liquid extraction mechanisms by quantum chemical methods

• Published in: Journal of molecular modeling 2012-11, Vol.18 (11), p.4909-4915
• Main Authors: Valente, Mário, Sousa, Sérgio Filipe, Magalhães, Alexandre L., Freire, Cristina
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Computer Appl. in Life Sciences; Computer Applications in Chemistry; Molecular Medicine; Original Paper; Theoretical and Computational Chemistry
• ISSN: 1610-2940; 0948-5023
• DOI: 10.1007/s00894-012-1491-3

In this paper we report a quantum chemical study performed at the B3LYP/6-311G++(d,p) level of theory on structural and energetic aspects of the sequential dehydration of a tetra-hydrated polyethylene-glycol type podand ( 1,2-bis-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-benzene , hereafter b33 ) and its complex with the K + cation. Thermodynamical parameters were determined by hessian quantum calculations performed using a self-consistent reaction field (SCRF) method, taking into account solvent (dichloromethane) effects. The results allowed the estimation of dehydration enthalpies, entropies and free energies for the hydrated free b33 podand and its corresponding K + cation complex in dichloromethane. The low absolute values found for the dehydration free energies as well as the structural features found for the optimized structures and the corresponding basis superposition calculated interaction energies, support the hypothesis of an interfacial complexation type mechanism governing the assisted extraction of K + from an aqueous toward an organic phase, in liquid/liquid extraction. Figure Stereo-view of the optimized structures of [Kb33(H 2 O)n] + complexes with n=0,1,2,3 and 4