Extraction selectivities of crown ethers for alkali metal cations: Differences between single-species and competitive solvent extractions

Separation factor values for pairs of alkali metal cations determined in co mpetitive solvent extractions of alkali metal picrates from aqueous solutio ns into chloroform by a variety of benzo- and cyclohexano-group-containing crown ethers vary significantly from extrapolations based upon the results of single-species extraction experiments. For almost all of the crown ether -alkali metal cation combinations examined, the separation factor values ar e greater for competitive solvent extraction. In view of the unexpected res ults for sodium picrate extraction by dibenzo-24-crown-8, the solid-state s tructure of the isolated complex was determined.