Metal complexes in solvent extraction—IV synergism and destruction of synergism with thenoyltrifluoroacetone and hexafluoroacetylacetone

Abstract

Tracer extraction studies have been carried out on the system 65Zn/HA/S, where HA = thenoyltrifluoroacetone (HTTA), hexafluoroacetylacetone (HHFA); S = tri-n-octyl phosphine oxide (TOPO), 2-ethyl-n-hexyl alcohol, methyl-n-hexyl ketone and chloroform. Equilibrium constants have been determined for the formation of the extracted species Zn(TTA) 2·TOPO, Zn(HFA) 2· TOPO and Zn(HFA) 2(TOPO) 2. Ultra-violet spectral studies and proton magnetic resonance studies were carried out in order to gain information on the decomposition of Zn(HFA) 2·(TOPO) 2. This work supports the proposal that synergism involves both the stability and solubility of binary and ternary complexes. It is suggested that the term “antisynergism” is a misnomer, in that the phenomenon is merely the destruction of synergism. The proposal is made that in the destruction of synergism in the HHFA system by excess TOPO from an aqueous HClO 4 solution, the over-all reaction may be written: Zn(HFA) 2·(TOPO) 2 + 2TOPO + 2H + + 4H 2O = Zn 2+ + 2 HHFA·2H 2O(TOPO) 2. When the aqueous medium is a buffer of pH 5, the over-all reaction becomes: Zn(HFA) 2·(TOPO) 2 + 2H 2O + 2S = Zn(HFA) 2·2H 2O + 2 TOPO-S. Here S = 2-ethylhexyl alcohol and chloroform, which are capable of hydrogen bonding with TOPO. When S = TOPO or methyl-n-hexyl ketone, no hydrogen bonding with TOPO occurs and there is no destruction of synergism from an aqueous buffer solution of pH 5.