Alkali and Alkaline Earth Metals

Abstract

The selective extraction of alkali metal ions made a dramatic step forward with the discovery of the crown ethers. These oxygen-containing macrocycles are important because they were the first compounds that allowed alkali metal ions to be solubilized in organic solvents. These compounds effectively extract alkali metal ions into an organic solvent from an aqueous phase, and by changing the cavity size within the macrocycle selectivity, between the different alkali metals can be achieved. More recently, chemically modified calixarenes have been found to be good extractants for these ions. The present state of the art in designing extractants for alkali metal ions involves incorporating a crown ether moiety onto a calixarene framework. The resulting calixcrowns can be highly selective complexants and extractants for the individual alkali metal ions. Although early research in seeking hosts focused on discovering extractants for the lighter alkali metals such as sodium, more recently the focus has been on cesium because of its presence as one of the radioactive metals in nuclear wastes.