Effects of Substituents in β-Diketones and Their Tris-iron(III) Complexes on Partitioning between Various Micellar Phases and the Bulk Aqueous Phase

Abstract

To determine the factors that affect the partitioning of solutes in micellar systems, we investigated the partitioning of several β-diketones and their tris-complexes with iron(III) between the bulk aqueous phase and micelles of various polyoxyethylene (POE)-type nonionic surfactants (C₁₂POE₈, Brij 35, Brij 58, and Triton X-100). The trends of the partition constants in the micellar systems differed from those in typical liquid–liquid systems; these differences may have been due to the effects of the substituent groups on the extractants, and to the effects of the inner-sphere chemistry of the micelles. The bulkiness and the low wettability of the extractants and the complexes hindered their extraction into the micellar phase. The interaction between the polyoxyethylene moiety of the surfactants and water molecules dissolved in the micellar mantle may have hampered the penetration of such solutes with bulky or low-wettability substituents into the mantle. The locus of the solutes in the micelles seemed to play an important role in the partitioning behavior.