The Extraction of the Chromium(III) Ion from Trichloroacetate Solutions to Inert Solvents Containing Trioctylphosphine Oxide

Abstract

Abstract Chromium(III) has been extracted with 0.1 mol dm−3 trioctylphosphine oxide(TOPO) in various inert solvents from a 0.1 mol dm−3 trichloroacetate(TCA−) buffer solution of pH 3.5 to 6.0. As diluents of TOPO, hexane and cyclohexane are most effective, while chloroform is quite ineffective. The extraction mechanism has been clarified by analyzing separately the distribution of water, trichloroacetic acid(HTCA), and the Cr(III) ion between the aqueous and organic phases. Water and HTCA are present in the cyclohexane phase as H2O·TOPO and HTCA·TOPO respectively. Chromium(III) is extracted with TOPO into cyclohexane as an ionassociation complex like Cr(H2O)63+(TCA−)3·3TOPO, and the extraction constant is 107.68. It is concluded that the hexahydrated Cr(III) ion is solvated by three molecules of TOPO, forming an ion pair with three trichloroacetate anions. The extractability of Cr(III) in the present system depends most effectively on the concentration of HTCA-free TOPO in the organic phase.