Silica gel-bound aza-crowns for the selective removal and concentration of metal ions
Silica gel-bound macrocycles have been prepared by first hydrosilylating a macrocycle-containing alkene with triethoxysilane followed by coating and heating the resulting macrocycle-containing triethoxysilane on 60-200 mesh silica gel. The macrocycle is attached to silica gel by stable hydrocarbon-ether groups. The aza- crown-containing alkenes were prepared in good overall yields by convenient three- and four-step reactions using N-(2-(2-~hloroethoxy)ethyl)acetamide as a synthon. The silica gel-bound macrocycles were found to be stable at aqueous pH values below 11. In numerous determinations, the log K values for the interaction of the bound- macrocycle with various cations were found to be similar to those for the analogous unbound macrocycle with the same cations in aqueous solution. This result indicates that the bound- and unbound-macrocycles are solvated and form complexes in the same manner. Several separations of heavy metal ions from aqueous mixtures of ions are described.