Solid-liquid (S-L) an liquid (L-L) phase transfer of salts via ‘encapsulated’ crown ether cation complexes

In recent years crown ethers have been successfully used for the transport of salts, both inorganic and organic, from an aqueous phase to organic solvents. Our work has extended the applicability of these crown ethers to the transport of salts from the solid state into solution both aqueous and nonaqueous. For this purpose a number of novel crown ethers have been synthesized that have in addition to a polar ‘cavity’ formed by donor atoms of the macrocyclic ring, (an) additional anionic functional group(s) covalently bound to the macroring. The first part of the lecture will deal with the design of such macrocycles that can encapsulate a spherical cation in a flexible cavity or that can encapsulate non-spherical cations. e.g. uronium cations, in a relatively rigid cavity. Together with the synthesis results of complexation studies using 1H NMR spectroscopy will be discussed. In the second part the use of crown ethers for the transport of sparingly soluble salts from the solid state into aqueous solutions will be dealt with. The emphasis will be placed on theoretical models that can be used to described such phase transfer processes and to predict thermodynamic stability constants of complexes required for solubilisation. The lecture will conclude with a comparison of these models with experimental results.