Bifunctional phosphoric acid–phosphine oxide extractants: synthesis and complexes with uranium-(IV) and -(VI) and iron(III)

Abstract

A bifunctional extractant (H L) carrying phosphine oxide and phosphoric acid complexing centres has been synthesized by the cyclic enediol phosphate method, using a two-step reaction with dihexyl (hydroxymethy1)phosphine oxide and 2-ethylhexanol. The bifunctional complexant complexes both UIv and Uv'. The complexation process, as shown by 31P n.m.r. spectroscopy, involves both the R3P=0 and (R'O),PO,H centres ( R=C6H,3, R' =C,H,,).The compound H L exists as hydrogen-bonded associates in the organic (hexane) phase. Involvement of anions in the complex structures is evident for Uv' ( NO3-), UIv( CI-, N O ; , or H PO,,-), and Fe( CIor SCN-).Complexing ligands of high affinity for metal ions can be either solvating or chelating donors.' Both classes are subject to strong competition from inorganic ligands. As a consequence of this competition, only chelating ligands that form stable ring systems are generally strong complexing ligands.The admixture of high concentrations of complexing agents in the appropriate solvents and in the right ratios provides, in some cases, an alternative to the careful design of bifunctional ligands. So-called 'synergistic' extractants show enhanced extraction power when mixed together, in comparison to the individual extractants in separate solutions.2aSynergistic extraction is a well known phenomenon in the extraction of uranium ions from phosphoric acid solution^.^-^The pair of extractants is composed of phosphoric acid esters, i.e. di(2-ethylhexy1)phosphate and trioctylphosphine oxide. This system has its limitations, under the following conditions:(1) either the extractant or metal-ion concentration is low;(2) extractants are diluted in a solid matrix, such as a polymeric carrier or membrane; and (3) in the presence of strong competing ions, such as a high concentration of phosphate ions.A bifunctional extractant composed of a molecule with two centres, a phosphine oxide and alkyl ester of phosphoric acid, linked through a spacer group, is proposed as a single molecular entity combining the overall properties of the synergistic single components. The synthesis of such bifunctional complexing

Reduction of Functionalized Tertiary Phosphine Oxides with BH3

“…The starting compounds: o -anisylphenylphosphine oxide, (1-naphthyl)phenylphosphine oxide, di- p -anisylphosphine oxide, di- p -fluorophenylphosphine oxide, di- p -tolylphosphine oxide, di(3,5-dimethylphenyl)phosphine oxide, tert -butylphenylphosphine oxide, benzylphenylphosphine oxide, phenyl(isopropyl)phosphine oxide, cyclohexylphenylphosphine oxide, di- c -hexylphosphine oxide, di- n -hexylphosphine oxide, methylphenylphosphine oxide, diphenylphosphine oxide, tert -butylmethylphenylphosphine oxide, and optically active tert -butylphenylphosphine oxide were prepared according to reported methods. Optically active o -anisyl(2-hydroxyethyl)phenylphosphine oxide was available from another studies…”

Stereoselectivity of Michael Addition of P(X)–H-Type Nucleophiles to Cyclohexen-1-ylphosphine Oxide: The Case of Base-Selective Transformation

“…Diphenylphosphine oxide ( 11a ), bis- p -anisylphosphine oxide ( 11b ), bis- o -tolylphosphine oxide ( 11c ), di- c -hexylphosphine oxide ( 11d ), di- n -hexylphosphine oxide ( 11e ), bis-1-naphthylphosphine oxide ( 11f ), bis- p -tolylphosphine oxide ( 11g ), o -anisylphenylphosphine oxide ( 11h ), optically active ( R P )- tert -butylphenylphosphine oxide (( R P )- 21 ), and optically active ( R P )- tert -butylphenylmethylphosphine oxide (( R P )- 14 ) were synthesized according to reported procedures. Diphenylphosphine was commercially available and used as received.…”

Uranyl-Selective Electrode Based on a New Bifunctional Derivative Combining the Synergistic Properties of Phosphine Oxide and Ester of Phosphoric Acid

“…A bifunctional compound, O -methyldihexylphosphine oxide O ‘-hexyl-2-ethylphosphoric acid, that possesses the properties of the two components of the above synergistic mixture in one entity has been prepared. − The linking of phosphine oxide and phosphate groups in the same molecule has resulted in an enhancement of the extraction capabilities (8.7 times stronger), due to the formation of a bimolecular complex (i.e., the extraction mechanism steps are simpler) . The synergistic effect of the two moieties of the molecule has been demonstrated as well by 31 P NMR, where it was observed that both phosphorus ligands participate in the complexation . This new reagent shows a considerable advantage in the extraction of U(VI) over synergistic mixtures of extractants in solvent extraction processes.…”

“…The mechanism of the synergistic extraction involves the formation of a trimolecular complex TOPO−UO 2 −D-2EHPA, where TOPO is responsible for pulling UO 2 2+ from the aqueous phase, and D-2EHPA improves the solubility of the complex in the organic phase . A bifunctional compound, O -methyldihexylphosphine oxide O ‘-hexyl-2-ethylphosphoric acid, that possesses the properties of the two components of the above synergistic mixture in one entity has been prepared. − The linking of phosphine oxide and phosphate groups in the same molecule has resulted in an enhancement of the extraction capabilities (8.7 times stronger), due to the formation of a bimolecular complex (i.e., the extraction mechanism steps are simpler) . The synergistic effect of the two moieties of the molecule has been demonstrated as well by 31 P NMR, where it was observed that both phosphorus ligands participate in the complexation .…”

“…In the present work, the bifunctional chelating agent, O -methyldihexylphosphine oxide O ‘-hexyl-2-ethylphosphoric acid (HL) (Figure ), incorporating a phosphine oxide and phosphoric acid diester functionalities, and its uranyl complex (UO 2 L 2 ), both synthesized in our laboratories, − are proposed as ionophores for the determination of uranyl ion. Flow-through tubular electrodes based on both ionophores are also studied as potentiometric detectors by flow injection techniques.…”