Extraction and transport of alkali metal salts by crown ethers and cryptands: estimation of extraction constants and their relationship to transport flux

Abstract

A method is described for the estimation of two phase extraction constants from stability constants for complexation of alkali metal cations by crown ethers and cryptands. The total free energy change for extraction of alkali metal salts from water to a non-polar organic solvent is evaluated as a sum of free energy terms for complexation, transfers of cation, anion, and complex between solvents, and ion pairing in the non-polar solvent. The method gives satisfactory agreement with a variety of published extraction constants and can be used predictively. As an example, the influence of extraction constant on transport flux was examined using calculated extraction constants and the rate data of Lamb etal. (J. Am. Chem. Soc. 102, 6820 (1980)); rates are adequately modelled by a simple analysis of diffusion.