The kinetics of extraction of zinc, nickel, cobalt, and cadmium with diphenylthiocarbazone, di-o-tolylthiocarbazone, and di-a-naphthylthiocarbazone were studied. Each of these reactions were first order in metal ion and, with one exception, first order in reagent anion. The reaction of zinc with di-a-naphthylthiocarbazone was second order in reagent anion. The rate constants for each metal ion paralleled the rate at which water dissociates from the hydrated metal ion. In every case sterically hindering substituents on the phenyl rings of the reagents increased the rate of the reaction. A mechanism is proposed in which the rate-controlling step is the reaction involving the change in configuration of the monodithizonate complex from six-to-four-coordinate metal ion, accompanied by the dissociation of water. Values of the distribution coefficients, Kd" of the reagents between CHCI3 and water are reported.

inner filter effect make a separation necessary. Salicylamide is not too soluble in aqueous acid so that some of it is eliminated in the dissolution step. The remainder is removed by an ether extraction.Sominex tablets were analyzed in triplicate by the procedure outlined in the Experimental section. Samples spiked with standard methapyrilene hydrochloride solu-tion were analyzed to determine the recovery. The mean of the results (Table VI) for methapyrilene was 0.9 mg higher than the stated amount of 25 mg on the label, a reasonable deviation.

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Chromium(III) has been reported to be non-extractable as an ion association complex with high molecular weight amines (1). This is probably due to the slowness with which the coordinated water molecules are replaced by negative ions. Stability constant data show that chromium(III) should form an anionic complex with thiocyanate which might be extractable as an ion association complex with high molecular weight amines (2). This study examines the extraction characteristics of such a system and attempts to separate other transition metal ions from chromium(III). EXPERIMENTAL Apparatus. A Tracerlab Model P-20D scintillation detector connected to a Model SC-71 scaler was used to count the gammaemitting isotopes in both the organic and the aqueous phases. An Eberbach water bath shaker was used for agitation of the samples.

The extraction constants (K*) for zinc(ll), cobalt(ll), and nickel(ll) were determined for the extraction of the metal ion from an aqueous phase into a chloroform solution of dithizone. The extraction constant for nickel (0.60) was significantly different from that reported by Koroleff (1.2 -3). This difference is attributable to the slow formation of the nickel dithizonate. As Zn(ll), Co(ll), and Ni(ll) cannot be separated by extraction with dithizone without the use of masking agents, the optimum conditions for the separation of the ion pairs Ni-Zn, Zn-Co, and Ni-Co, based on the differences in the rates of formation of the metal dithizonates, were determined. More than 99% of Zn could be extracted while only 2.5% of Ni extracted. The optimum conditions determined for the separation of Zn from Co resulted in extraction of 96% Zn with only 8.6% Co extracting. The separation of Co from Ni was less effective, because of the similarity in extrac-'To whom inquiries should be addressed.