A MOLECULAR MODELLING STUDY OF DIBENZOYLTARTRATE EXTRACTION BY MONO- AND DICATIONIC EXTRACT ANTS

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Abstract
Molecular modelling is used as a novel aid to account for the results of solvent extraction of dianionic species such as dibenzoyltartrate with monocationic extractant (butyltrioctylphosphonium) and dicationic extractants such as polymethylenebis(trioctylphosphonium)s abbreviated as CnBPs. The extraction ability of CnBPs was remarkably dependent on the length of bridging methylene chain connecting the two phosphonium cationic centers which offers an effective molecular recognition field. The anionic species and cationic extractants are modelled separately in their conformations corresponding to the absolute energy minimum. Then, 1:1 and 2:2 ion-pair complexes are built and minimized by taking into account their atomic charge distributions. The minimized energies quantify the steric and electrostatic effects of complexes. The results show that the 2:2 association takes the best account for experimental data and that the electrostatic energy is an important component of the total energy of complexes. The maximum extraction ability which is obtained with C6BP corresponds to the more stable complex characterized by the lowest values of total and electrostatic energies. Graphical relationships have been obtained between the total energy or electrostatic energy and the coefficient of distribution.