SOLVENT-EXTRACTION OF RADIUM WITH CROWN-ETHER CARBOXYLIC-ACIDS

The capabilities of a series of 11 crown ether carboxylic acids with d ifferent hydrocarbon substituents have been evaluated for solvent extr action of radium in aqueous solutions. The extraction of radium procee ds from alkaline media into chloroform solutions of the crown ethers. The extraction requires no specific counteranions and is reversible wi th respect to pH. Substitution of tert-butyl groups in the benzene rin gs of sym-dibenzo-16-crown-5-oxyacetic acid increases the lipophilicit y of the macrocyclic compound and enhances the extraction efficiency f or radium. Radium forms a RaL(2)-type complex with this tert-butyl-sub stituted crown ether carboxylic acid with a binding constant of (4.2 /- 0.7) x 10(8).