Vìsnik Odesʹkogo Nacìonalʹnogo Unìversitetu: Hìmìâ (May 2018)
THE PECULIARITIES OF THE COMPLEXATION OF Co(II) WITH 4-SULFO-2 (4'-SULFONAFTALIN-1'-AZO)-NAPHTHOL-1 IN SOLUTIONS
Abstract
In this paper, the features of the complexation of the “Cobalt(II) -carmoazine-H2O2” system were studied spectrophotometrically. It is shown that the complexation of carmoazine (CAN) with Co(II) is possible only after its oxidation in the presence of hydrogen peroxide. In contrast to the previously investigated ions of variable valency metals that interact with carmoazine according to the mechanism of mutual oxidationreduction, in this case, carmoazine acts as a typical organic ligand. The optimal conditions of interaction in the investigated chemical system (pH 8, 10 vol% H2O2) were established. The complex composition (Co(III):KAN = 1:3) was determined by classical spectrophotometric methods (molar ratios and equilibrium shift). Using the Komar method molar absorbtivity of the complex was calculated (ε600 = 5300). The complex stability constant which is 2.4 ∙ 109, was calculated. The presence of Co(III) ions in the newly formed as a result of the oxidation-reduction reaction to the chemical system was proved by using the intake of “interception” of trivalent cobalt ions by the competing ligand – EDTA. The charge (-6) of the product of interaction in the system “Cobalt(II) -carmoazine-H2O2” was determined by the extraction spectrophotometric method. Given the stoichiometry of the complex and the presence in the molecule of carmoazine of two negatively charged outer-sphere sulfo groups, as well as the positive charge of cation of cetylpyridinium (CP+Сl-), the composition of the ion pair extracted with chloroform [Co(III) · 3CAN2- · 6CP+] was determined. An assumption was made about the mechanism of interaction of Co (II) with carmoazine, which is preceded by the oxidation stage of Co(II) in Co(III) to form the transition peroxide complex and its subsequent complexation with carmoazine by the acid-base mechanism.
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