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

Abstract

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 R₃PO and (R′O)₂PO₂H centres (RC₆H₁₃, 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^–).