Extraction of selected tervalent lanthanides with N-phenylacylhydroxamic acids

the extraction behavior of certain tervalent lanthanides into chloroform solutions containing various N-phenylacylhydroxamic acids is reported. The ligands include N-o-methylphenyl-m-trifluoromethylbenzohydroxamic acid (MPFBHA), N-m-trifuloromethylphenyl-o-methylbenzohydroxamic acid (FPMBHA), N-o-methylphenylbenzohydroxamic acid (MPBHA), N-phenyl-o-methylbenzohydroxamic acid (PMBHA), N-o-methylphenyl-p-tertbutylbenzohydroxamic acid (MPBBHA), and N-phenyl-p-tert-butylbenzohydroxamic acid (PBBHA). Of the N-phenylacylhydroxamic acids mentioned, only PBBHA was found suitable to extract the lanthanides under the experimental conditions used. The selected lanthanides, namely La, Pr, Eu, Ho, and Yb, were all found to extract with PBBHA as self-adducts of the form LnL₃ · 2 HL, where L and HL denote the ligand anion and neutral ligand, respectively. The extraction constants and separation factors for the lanthanides with PBBHA were evaluated. It is possible that steric hindrance prevents the lanthanides from extracting with MPFBHA, FPMBHA, MPBHA, PMBHA, or MPBBHA.