would result in an increase in the corrected heterogeneous rate constants, kh*
= hPfRakh
(4)
where kh* is the heterogeneous rate constant corrected for both Frumkin double-layer eKects and activity effects. As the activity corrections sh media than in the perch probable overlap in the rate constant values corrected for both Frumkin double-layer effects, and for activity effects would be more complete than the overlap apparent in the values tabulated in Table 111.
ACKNOWLEDGMENT
Th tions J. D. MCLEAN TIMNICK ANDREW Michigan State sity East Lansing, Mich. 48823 RECEIVED for review July 31, 1967. Accepted August 16, 1967.
Kinetics and Mechanism of Extraction of Cobalt(l1) with Subst it uted Dipheny Ithiocarbazones
f these chelates was faster than that metal ion would shed light
EXPERIMENTAL
The apparatus materials, experimental procedures, and methods of treating the data have been previously reported (I, 2). The results are listed in Table I. DISCUSSION
studied Ni(I1) and Zn(I1) cases, the ted dithizones with 1 and reagent anion. effect of substituents on the rate of Co(I1) co resembles that for the Ni(I1) rather than the Zn(I1) series. This is particularly noticeable in the di-p-tolylthiocarbazone reactions for which both Co(I1) and Ni(I1) are slower than that with the corresponding di-p-iodo derivative, whereas the reverse is true with zinc. With the present data, it is now possible to link the mechanism of the chelation reaction more closely with that of water substitution in the first coordination sphere of the metal ion. There is a nearly linear relationship between the logarithm of the rate constants of water substitution and chelate formation for the metals studied in this series. The average slope of these parallel lines is 0.85 0.15 (A log kHtO/A log k M L ) with only one significant exception, that of the di-o-tolyl derivative. The line segment between the points for Ni and Co has a slope within the range of the average slope, but the exceptionally low value of the rate constant of zinc with this ligand imparts a
*
(1) J. S.Oh and H. Freiser, ANAL.CHEM., 39, 295 (1967). (2) B. E. McClellan and H. Freiser, Ibid., 36,2262 (1964).
Table I. second-Order Rate Constants for Formation of 1:l Cobalt(I1)-Dithizone Chelates at 25" C and fi = 0.1 Diar ylthiocarbazone Diphenyl4.94 Di-p-bromophenyl6.69 Di-p-iodophenyl7.18 Di-o-tolyl5.88 (3) Di-p-tolyl6.87 Di-p-methoxyphenyl6.58 a Reported value at p = 0.1 (2).
slope of 1.85 to the segment between Co(I1) and Zn(I1). These results emphasize the sensitivity of the reaction with zinc to adverse steric influences in the dithizone series. The rates of the Co(I1) reactions displayed the parabolic relation to the Hammett CT constants of the substituents shown by both Ni and Zn in the earlier study. The explanation for this general trend remains elusive. Although not as rapid as the corresponding Zn(I1) reactions, the Co(I1) reactions are about two orders of magnitude faster than those of Ni(I1) which should provide a sufficient difference on which to base differential extraction methods. JOONS. O H L ~ HENRYFREISER Department of Chemistry University of Arizona Tucson, Ariz. 85721 1
On leave from Seoul National University, Seoul, Korea.
RECEIVED for review June 29, 1967. Accepted August 10, 1967. Work supported by the National Science Foundation under Grant No. GP-6004. (3) Sister M. Cordes, University of Arizona, unpublished work,
1967.
VOL. 39, NO. 13, NOVEMBER 1967
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