Anion Effect on the Solvent Extraction of Alkali Cations with Dibenzo-18-crown-6 in 1,2-Dichloroethane. Voltammetric and Spectroscopic Analysis

Abstract

The alkali cations (M + ) extraction process from water to 1,2-dichloroethane (DCE) with dibenzo 18-crown-6 (DB18C6) using either picrate (Pi-) or 2,4-dinitrophenolate (DNP-) as counter ions (A-) is analyzed. Picrates are extracted in a higher extent as a consequence of its higher hydrophobicity. Extraction constants (K ext ) were determined analyzing the organic phase resulting of the extraction process, either spectrophotometrically or voltammetrically against an aqueous phase containing LiCI. A very good agreement between both methods was obtained except for Cs + . The extraction using DNP can only be performed provided it is initially present in the aqueous phase. On the other hand, if HDNP is present in the organic phase the extraction process does not occur even at high pH values of the aqueous phase due to the strong interaction with DB18C6. Ion pair constants (K 1P ) were determined from K ext and Gibbs energy of M + and A - transfer.