New Nitrogen-Containing Macrocyclic Ligands Covalently Attached to Silica Gel and Their Use in Separating Metal Cations

Several polyaza-crowns and cyclams, each containing an allyl-oxymethyl or other monofunctional group capable of further reaction to attach it to silica gel, have been prepared. As an example of an attachment of a crown to silica gel, allyloxymethyl-substituted diaza-18-crown-6 was reacted with triethoxysilane to form the crown-substituted triethoxysilane This crown-silane material was heated on silica gel to effect a covalent attachment of the crown. The silica gel-bound macrocyclic ligands were found to interact with various metal cations with log K ( H2O) values similar to those of the same cations with unbound macrocycles. A tetraaza-crown bound to silica gel was found to quantitatively remove toxic heavy metal ions, such as Pb2+, Hg2+ Cd2+ Ag+and others at the ppb level, from large volumes of aqueous solutions containing those metal ions and much larger amounts of Na+Mg2+and Ca2+ions