EXTRACTION OF ALKALI-METAL CATIONS BY LIPOPHILIC DIBENZO-14-CROWN-CARBOXYLIC ACIDS

The extraction of alkali metal cations by the lipophilic crown ether, bis-t-octylbenzo-14-crown-4 (BOB14C4), three derivatives of BOB14C4 ha ving pendant carboxylic acid sidearms, and a lipophilic carboxylic aci d, 2-methyl-2-heptylnonanoic acid (HMHN) was studied by two-phase pote ntiometric titration and ion-chromatography. The lipophilic, ionizable crown ethers, BOB14C4-acetic acid (BOB14C4AA), BOB14C4-propanoic acid (BOB14C4PA), and BOB14C4-oxyacetic acid (BOB14C4OAA) extract cations efficiently from aqueous mixed alkali metal chloride solutions into 1- octanol by an ion-exchange mechanism in the range p[H] > 7, as does HM HN. The mode of attachment of the ionizable sidearm, via an ether link age (BOB14C4OAA) versus a carbon linkage (BOB14C4OAA and BOB14C4PA), h as a significant effect on the cation selectivity and extraction effic iency of these extractants. BOB14C4 exhibits no p[H] dependent extract ion behavior and has no significant effect on the extraction of alkali metal cations by HMHN in a mixture of these two compounds. Although B OB14C4AA and BOB14C4PA extract cations at lower p[H] than HMHN, all th ree compounds exhibit similar selectivity for Li+ over Na+, K+, Rb+, a nd Cs+. A significant reversal in selectivity is observed with BOB14C4 OAA, which extracts Na+ and K+ selectivity over Li+, Rb+, and Cs+ and at significanty lower p[H] than BOB14C4AA, BOB14C4PA, or HMHN. The uni que behavior of BOB14C4OAA may be attributed to the presence of the et her linkage between the crown ether and the pendant carboxylic acid.