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

A bifunctional extractant (HL) carrying phosphine oxide and phosphoric acid complexing centres has been synthesized by the cyclic enediol phosphate method, using a two-step reaction with dihexyl(hydroxymethyl)phosphine oxide and 2-ethylhexanol. The bifunctional complexant complexes both U^IV and U^VI. The complexation process, as shown by ³¹P n.m.r. spectroscopy, involves both the R₃P=O and (R′O)₂PO₂H centres (R=C₆H₁₃, R′=C₈H₁₇). The compound HL exists as hydrogen-bonded associates in the organic (hexane) phase. Involvement of anions in the complex structures is evident for U^VI(NO₃^-), U^IV(Cl^-, NO₃^-, or HPO₄^2-), and Fe(Cl^- or SCN^-).