Electrochemical detection and evaluation of the anomalous chloride extraction from water to 1,2-dichloroethane under the non-equilibrium conditions

Abstract

Anomalous chloride extraction from water to 1,2-dichloroethane is detected by cyclic voltammetry and evaluated by the potential step amperometry of the background electrolyte combined with the open circuit potential measurements. The extraction process is affected by the composition of the organic phase. In the present study, the latter effect is elucidated and the mechanism of the solvent extraction of chloride is proposed. The mechanism couples the energetically unfavourable extraction of a hydrophobic salt (e.g., tetrapentylammonium tetraphenylborate, bis(triphenylphosphoranylidene) ammonium tetraphenylborate) from the organic to the aqueous phase with the favourable extraction of the chloride salt of the present hydrophobic cation in the opposite direction resulting in the chloride accumulation in the organic solvent phase. An evaluation and analysis of the ion flux suggests that the chloride anions are extracted to the organic phase in the form of the free anions and the anions bound to the ion-pairs, and for the most part as the hydrated salt clusters, the formation of which is likely to be the driving force of the extraction process. The transfer of the accumulated chloride anion back to the aqueous phase is responsible for the positive current shift of the cyclic voltammogram and the steady-state positive current recorded in the potential step amperometric measurements. First application of the novel potentiostatic assembly introducing the polarizable reference electrode for the organic solvent phase is demonstrated.