STUDY OF PROTOLYTIC EQUILIBRIA IN SOLUTIONS OF HYDROXYANTHRAQUINONE DYES BY CHEMICAL CHROMATICITY METHOD

In this paper, the acid-base properties of hydroxyanthraquinone dyes-alizarin, alizarin red S and alizarin-complexone- were studied in aqueous solutions by chemical chromaticity and spectrophotometry methods. The advantages of chemical chromaticity method over UV-VIS spectrophotometry method were shown in the protolytic equilibria study in dyes solutions. The chemical chromaticity method, unlike spectrophotometry, can determine the deprotonation constant of sulfo group of alizarin red S. Using the chromaticity functions data it is possible to determine all ionization constant of these hydroxyanthraquinone dyes. The overlay of tautomeric equilibria on alizarin-complexone ionization process does not interfere for pK determination of their functional groups by the chemical chromaticity method. A quantitative color description of objects of different nature by calculating their color coordinates by spectrophotometric data allows distinguishing spectrally similar substances and obtaining new data on them. Using the values of chromaticity functions of ion-molecule forms of the hydroxyanthraquinone dyes as an analytical signal allows to get a complete picture of the existing acid-base equilibria in a wide range of medium acidity. A probable acid-base equilibria schemes were theoretically determined for alizarin, alizarin red S and alizarin-complexone using CNDO calculations. The diagrams of the ion-molecular forms distribution of hydroxyanthraquinone were built.For citation:Chebotarev A.N., Snigur D.V., Bevziuk K.V. Study of protolytic equilibria in solutions of hydroxyanthraquinone dyes by chemical chromaticity method. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 22-28.