Crown ether as size selective synergist in the solvent extraction of thorium(IV) and uranium(VI) with 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone

The synergistic extraction of thorium(IV) and uranium(VI) from nitric acid solutions has been investigated using mixtures of 3-phenyl-4-(4-fluorobenzo yl)-5-isoxazolone (HFBPI) and dicyclohexano-18-crown-6 (DC18C6), dibenzo-18 -crown-6 (DB18C6) or benzo-15-crown-5 (B15C5). The results demonstrate that these metal ions are extracted into chloroform as Th(FBPI)(4) and UO2(FBPI )(2) with HFBPI alone and as Th(FBPI)(4). CE and UO2(FBPI)(2). CE in the pr esence of crown ethers (CE). The equilibrium constants of the above extract ed complexes have been deduced by nonlinear regression analysis. The additi on of a crown ether to the metal chelate system enhances the extraction eff iciency and also improves the selectivities significantly between thorium ( IV) and uranium(VI). The complexation strength of uranium(VI) with various crown ethers follows the order: DC18C6 > B15C5 > DB18C6, which can be expla ined on the basis of crown ether basicity sequence and steric effects. On t he other hand, the complexation strength of Th-FBPI chelate with crown ethe r follows the order: B15C5 > DC18C6 > DB18C6. The high extraction of thoriu m(IV) with B15C5 can be explained on the basis of 'size-fitting effect'. So lid complexes of these metals with 4-acyl-3-phenyl-5-isoxazolones and with mixtures of HFBPI and crown ether have been isolated and characterised by e lemental analyses, IR and (HNMR)-H-1 spectroscopic techniques.