Synergistic effects in the extraction of metal ions by mixtures of dialkylphosphoric acids and substituted crown ethers.

Abstract

The extraction of alkaline earth cations from weakly acidic solutions by three dialkylphosphoric acids and various isomers of dicyclohexano-18-crown-6, both alone and in combination in toluene solutions, has been examined to determine the effect of both the crown ether stereochemistry and the structure of the organophilic anion on the magnitude of the synergistic effects. The synergistic effects have been found to differ considerably among the crown ether isomers and to vary with the extent of alkyl chain branching in the dialkylphosphoric acid. Attempts to correlate the synergistic effects with ligand strain energies from molecular mechanics calculations are described