Synergistic effect of nitrogen neutral bases in the solvent extraction of zinc(II) and cadmium(II) diphenylcarbazonates.

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The extraction behavior of zinc and cadmium with diphenylcarbazone(DPC) into benzene and chloroform were studied in both the absence and presence of neutral bases(S). In the case of chloroform, all of the neutral bases gave rise to adduct complexes with the formula of M(DPC)2S. On the other hand, in the case of benzene, the adduct complexes can be represented as M(DPC)2S for all neutral bases except for 1,10-phenanthroline(phen), in which the adduct complexes can be expressed as M(DPC)2(phen)2. The stability of the adduct complexes is related not only to the basicity of the bases, but also to the steric effect attributable to substitution. Furthermore, the adduct-formation constant increase in the following order against the normalized values of basicity: pyridine bases<2,2′-bipyridyl<1,10-phenanthroline derivatives. This order agrees with the increasing order of the coordinated ability as ligands. The basicity of the bases has a larger effect on the adduct-formation constants for Cd than on those for Zn. This may be attributed to the fact that Zn chelates have greater stability than the Cd chelates, as a result, the "residual Lewis acidity" of Zn is smaller than that of Cd, and therefore zinc chelates form less stable adducts.
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