INFLUENCE OF EXTRACTANT STRUCTURE ON EXTRACTION OF NITRIC-ACID AND AMERICIUM(III) WITH DIARYL(DIALKYL)[DIETHYLCARBAMOYLMETHYL]PHOSPHINE OXIDES

A study has been made of nitric acid and americium(III) extraction wit h dichloroethane solutions of dialkyl-(diaryl)[diethylcarbamoylmethyl] phosphine oxides containing various substituents (alkyl, aryl, alkoxyl , and mixed-ligand) at the phosphorus atom. Nitric acid is extracted a s complexes containing one, two, or three acid molecules per molecule of the reagent. The effective constants of the nitric acid extraction by all the reagents <(K)over bar(ex)(HNO3)> have been evaluated. The < (K)over bar(ex)(HNO3)> values linearly correlate with the ligand basic ity (pK(a)). All the reagents extract americium(II) complexes with two molecules of reagent. The effective constants of americium(III) extra ction <(K)over bar(ex)(Am)> have been evaluated; no general correlatio n between <(K)over bar(ex)(Am)> and pK(a) has been found. However, the following partial linear dependences between <(K)over bar(ex)(Am)> an d pK(a) have been determined: the direct dependence <(K)over bar(ex)(A m)> increases with increasing pK(a) in the case of successive substitu tion of alkoxy groups by phenyl groups, the reverse dependence in the case of successive substitution of alkyl groups by phenyl groups, whic h illustrates the ''anomalous aryl strengthening.'' and the direct dep endence in the case of introduction of substituents in benzene rings b onded to the phosphorus atom. It has been found that in the case of th e reagent containing tert-butyl radicals at phosphorus, <(K)over bar(e x)(HNO3)> and <(K)over bar(ex)(Am)> fall out of the linear dependences , probably owing to the prevalence of steric factor in the complex for mation.