SOLVENT-EXTRACTION OF THE HEXAAQUARHODIUM(III) ION FROM HALOGENATED CARBOXYLATE SOLUTIONS WITH TRIOCTYLPHOSPHINE OXIDE

The extraction equilibrium of the inert hexaaquarhodium(III) ion has been studied. Rhodium(III) was quantitatively and rapidly extracted from 0.10 mol dm-3 trichloroacetate (TCA) or 0.010 mol dm-3 pentadecafluorooctanoate solutions to heptane containing 0.10 mol dm-3 trioctylphosphine oxide (TOPO) at pH 3-5. The extraction equilibria were achieved within 1 min at 298 K. From the equilibrium study in the TCA-TOPO system, the rhodium(III) species extracted into heptane was found to be Rh.3TCA.4TOPO, and the extraction constant was 10(12.29). The rhodium(III) species in the organic phase was suggested to be the hexaaquarhodium(III) complex associated with TCA and TOPO.