Gibbs energies of transfer of chiral anions across the interface water|chiral organic solvent determined with the help of three-phase electrodes

Abstract

For the first time the differences in free energies have been experimentally determined for the solvation of two enantiomeric ions in two enantiomeric solvents. Three-phase electrodes consisting of a droplet of a solution of decamethylferrocene in a chiral solvent (D- and L-2-octanol) attached to a graphite electrode and immersed in an aqueous solution containing chiral anions, allow the measurement of these data for the transfer of the enantiomeric ions across the water|chiral solvent interface. In all studied combinations the Gibbs energy to transfer an L-ion from water to the L-solvent was equal to the Gibbs energy of transfer of the D-ion from water to the D-solvent, and the same was found for the transfer of a L-ion from water to the D-solvent and for the D-ion from water to the L-solvent. In all cases, the combinations D-anion/D-solvent and L-anion/L-solvent have smaller standard Gibbs energies than the combinations D-anion/L-solvent and L-anion/D-solvent. This can be explained by less favourable interactions between an anion and a solvent molecule in the latter cases.