A lipophilic diphosphonium salt 1 having binaphtyl-type axial chirality was developed as a novel ion-pair extractant. By use of (R)-1,(−)-di-O-benzoyltartrate ((−)-DBT) was extracted more effectively than (+)-DBT. The enantioselectivity (α= D (−)⁄ D (+); D: distribution ratio) was 1.3–1.4. When monophosphonium-type extractants (2 and 3) having structures similar to that of 1 were used, the enantioselectivity was heavily lowered. Equilibrium studies ...
