Kinetic and Spectral Studies of Cobalt (II) -4, 4’, 4’’, 4’’’ –Tetrasulfophthalocyanine with Sodium Cyanide in Aqueous Solution

Authors

Pablo J. Diaz Cruz

Publication Date

12-1982

Advisor(s) - Committee Chair

Robert Farina, Lawrence Boucher, John Riley

Degree Program

Department of Chemistry

Degree Type

Master of Science

Abstract

Kinetic studies of the cobalt (II)-4, 4’, 4’’, 4’’’-tetrasulfophtalocyanine and cyanide system were performed under argon and in air over temperature ranges of 294-314°K and 294-324°K, respectively. Two reactions were detected under argon. One was quite rapid and was followed on the stopped-flow apparatus. The results are consistent with the perturbation of a monomer-dimer equilibrium. The second reaction was slow enough to be followed spectrophotometrically on the Cary Model 14 spectrophotometer. The second order rate constant of 0.11 M^-1 sec^-1 at 294°K has been attributed to the rate of substitution of the second cyanide addition to a dye-cyanide complex. Activation parameters, ΔH* and ΔS* were obtained over a temperature range of 294-314°K yielding values of 3 +/- 0.3 kcal/mol and -56 +/- 5 e.u., respectively.

Reexamination of this system in air revealed three reactions. The first reaction was rapid and measurable on the stopped-flow apparatus. This reaction has been interpreted as a perturbation of the monomer-dimer equilibrium. The other reactions were monitored o the Cary Model 14 spectrophotometer and produced a biphasic curve. The slower reaction yields a rate constant, k_s of 3.4 +/- 0.15 x 10^-3 s^-1 at 294°K and is in agreement with the value reported for the dissociation of the dimer when corrections are made for differences in ionic strength. The activation parameters ΔH* and ΔS* for the slow step were calculated to be 9.1 +/- 0.9 kcal/mole and -39 +/- 3 e.u., respectively, over a temperature range of 294-324K. We have no good explanation for the faster step, k_f. However, a linear plot of 1n (dye concentration) vs. time shows k_f is a first order rate constant with a value of 2.0 +/- 0.15 x 0.10^-2 s^-1 at 294°K. There was no dependency of k_f on oxygen concentration, thus oxidation involving molecular oxygen is excluded as a possible step Moreover, there is no simple relationship between k_f and cyanide concentration. Activation parameters, ΔH*_f and ΔS*_f of 7.6 +/- 0.5 kcal/mole and -40 +/-4 e.u., respectively, were obtained over a temperature range of 294-324°K.

Disciplines

Analytical Chemistry | Chemistry

Recommended Citation

Cruz, Pablo J. Diaz, "Kinetic and Spectral Studies of Cobalt (II) -4, 4’, 4’’, 4’’’ –Tetrasulfophthalocyanine with Sodium Cyanide in Aqueous Solution" (1982). Masters Theses & Specialist Projects. Paper 1676.
https://digitalcommons.wku.edu/theses/1676