EXTRACTION OF ZINC AND CADMIUM WITH SOME BIS (5'-HYDROXY-PYRAZOL-4'-OYL) ALKANES AND TRI-N-OCTYLPHOSPHINE OXIDE IN CHLOROFORM

The extraction of zinc and cadmium with bis(5'-hydroxy-pyrazol-4'-oyl)alkanes (''HL-n-LH'', n: number of methylene links), with and without TOPO, in chloroform, has been studied when possible. The formation of third phases and/or precipitates hinders a number of extractions with HL-n-LH alone: Cd(II) for all extractants, Zn(II) for n < 7. The following species are extracted with cadmium: Cd(L-n-L)(TOPO)2 for n = 5, 7 to 10, Cd(L-8-L)(TOPO), Cd(L-8-LH)2(TOPO)2, Cd(L-8-LH)2(TOPO), and with Zn: Zn(L-n-LH)2 for n = 7 and 8, Zn(L-n-L) for n = 9 and 10, Zn(L-n-LH)2(TOPO) for n = 5 and 7, Zn(L-n-L)(TOPO) for n = 7 to 9. The polymethylene chain length effect upon the extraction processes is attributed to a relative destabilization of Zn(L-n-L) with respect to Zn(L-n-LH)2 for short-chain ligands, and conversely, to a preferential solvation of Zn(L-n-LH)2(TOPO), complexes by chloroform. The former may be due to some strain in the tetradentate ligand folded onto zinc. The latter is attributed to H-bond formation between the free -LH sites and the diluent. Compared with the parent compound 1-phenyl-3-methyl-4-benzoylpyrazol-5-ol the bis(acylpyrazolols) show a better Zn/Cd extraction selectivity.