MACROCYCLE METAL CATION INTERACTIONS INVOLVING POLYAZA MACROCYCLES BONDED TO SILICA-GEL VIA A NITROGEN DONOR ATOM

Macrocycles are noted for the remarkable selectivities which certain of them show toward metal ions. This selectivity has been studied extensively for free macrocycles in single solvent systems. However, there is a need for new systems that are more economical and with engineering feasibility which incorporate macrocycles to perform actual separations. Stable silica gel-bound macrocycles maintain the macrocycle for reuse in performing actual separations. The polyaza macrocycles 1,4, 7,10-tetraaza-18-crown-6, pentaaza-15-crown-5, and hexaaza-18-crown-6 have been synthesized with the macrocycle covalently bonded to silica gel via one of the nitrogen donor atoms. These bound macrocycles have selective and strong interactions with the soft heavy metal cations as well as proton chemistry which have now been quantified by the measurement of equilibrium constants. These interactions are similar to those of the analogous unbound macrocycles. Separations of ppb levels of heavy metal cations from concentrated matrices of other cations such as the alkali and alkaline earth cations have also been made. The bound macrocycles apparently show a greater tendency towards cavity size-based selectivity than the analogous unbound ligands. This is presumably due to increased ligand rigidity caused by the donor atom attachment to the solid support. © 1990 IUPAC