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 UIV and UVI. 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 UVI(NO3 ), UIV(Cl, NO3 , or HPO4 2–), and Fe(Cl or SCN).