Studies of the Liquid-Liquid Partition Systems. VIII. Stabilities and Extractabilities of Copper(II) and Zinc(II) Complexes with Acetylacetone, Trifluoroacetylacetone, and Hexafluoroacetylacetone in Aqueous Sodium Perchlorate Solution-Carbon Tetrachloride Systems

Abstract

Abstract The distribution of copper(II) and zinc(II) chelates with three β-diketones, acetylacetone (AA), trifluoroacetylacetone (TFA), and hexafluoroacetylacetone (HFA) between carbon tetrachloride and aqueous sodium perchlorate solutions at 0.1m, 1m, and 3m has been determined at 25°C as a function of the concentration of the dissociated chelate anions. The stability constants for the metal chelates in the aqueous phase and the two phasedistribution constants for the uncharged complexes have been determined by a graphic analysis of the distribution data. The distribution was also measured when the carbon tetrachloride phase was added with tributylphosphate (TBP) or trioctylphosphine oxide (TOPO) and the adduct-formation constants of the uncharged chelate with these ligands have been determined by a graphic analysis of the increase in the distribution ratio as a function of the ligand concentration. The results are as follows: (i) Copper(II) forms first and second complexes with these chelating ligands in the aqueous phase, whereas zinc (II) forms the third complex (except with HFA) besides the first and the second ones; the complexes are more stable in the ligand order of AA>TFA>HFA. (ii) The stability constants of the copper(II) complexes are much higher than those of the corresponding zinc(II) complexes. (iii) The distribution constant of the uncharged copper(II) complex is higher than that of the corresponding zinc(II) complex. (iv) No remarkable relation has been found among the distribution constants of the chelating acid and those of the uncharged metal chelates. (v) The adducts of the metal chelates are more stable in the ligand order of HFA>TFA>AA. The zinc(II) complex forms more stable adducts than does the corresponding copper(II) complex, and TOPO forms more stable adducts than does TBP. (vi) Changes in the concentration of the background salt alter the stability constants of the metal chelates and the distribution constants of the uncharged chelate (salting-out); the effects are, however, very complicated. On the basis of these results, the distribution constants of the uncharged chelates were discussed from the standpoint of the interactions of the central metal ions in the complexes with the water molecules, and a qualitative relationship between these interactions and the stabilities of the adduct chelate complexes was pointed out.