The synergic extraction of rare earth metals with ortho-substituted 1-phenyl-3-methyl-4-aroyl-5-pyrazolones and trioctylphosphine oxide

The synergic extractions of rare earth metals (scandium, lanthanum and lutetium, M3+) with ortho-substituted 4-aroyl derivatives of 1-phenyl-3-methyl-5-pyrazolone (HA) and a neutral ligand, trioctylphosphine oxide (TOPO, L) in benzene were studied. Eight ortho-substituted 4-aroyl derivatives of pyrazolone have been prepared. Linear relationships between the extraction constants and the acid dissociation constants of aroylpyrazolones were obtained when TOPO was not added. The metal chelates of aroylpyrazolones react with TOPO to form MA3L and MA3L2 types of adducts in the synergic extractions. Obvious steric hindrances of the terminal substituents at ortho-position of 4-aroyl group of the ligands on the adduct formation reaction were observed by the comparison of adduct formation constants.