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Protolytic Equilibria in Organized Solutions: Ionization and Tautomerism of Fluorescein Dyes and Related Indicators in Cetyltrimethylammonium Chloride Micellar Solutions at High Ionic Strength of the Bulk Phase

Department of Physical Chemistry, V. N. Karazin Kharkov National University, 61022 Kharkov, Ukraine
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Received: 25 December 2020 / Revised: 19 January 2021 / Accepted: 27 January 2021 / Published: 20 February 2021
Ionic equilibrium of 22 hydroxyxanthenes, including halogen and nitro derivatives of fluorescein, and their thio- and aza analogues, were studied spectrophotometrically in micellar solutions of cetyltrimethylammonium chloride at ionic strength of the bulk phase 4.0 M KCl. This micellar pseudophase is characterized by the electrostatic surface potential of +(15–16) mV and the ETN value of 0.623. In the case of dyes bearing the COOH group, colorless lactone is the predominant tautomer of the molecular form H2R. A new classification of fluoresceins is developed. The dyes were divided into four groups based on the nature of tautomerism of the anions. In the case of the fluorescein type, the monoanions HR exist predominantly as “carboxylate” tautomers, with ionized carboxylic and non–ionized hydroxylic group. For the dyes of the eosin type, the situation is opposite, while for the intervening type of compounds, the concentrations of the two tautomers are comparable. Dyes capable of forming lactone anions HR were classified as the fourth type. For some of them, even the dianion R2− exists as a lactone. The relationship between the stepwise ionization constants, Ka1/Ka2, varies from 1.3 to 1.07 × 105 and is determined by the state of tautomeric equilibrium of molecules and ions. View Full-Text
Keywords: fluorescein; xanthene dyes; cationic surfactant micelles; absorption spectra; apparent ionization constants; tautomerism of molecules and anions fluorescein; xanthene dyes; cationic surfactant micelles; absorption spectra; apparent ionization constants; tautomerism of molecules and anions
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MDPI and ACS Style

Mchedlov-Petrossyan, N.O.; Vodolazkaya, N.A. Protolytic Equilibria in Organized Solutions: Ionization and Tautomerism of Fluorescein Dyes and Related Indicators in Cetyltrimethylammonium Chloride Micellar Solutions at High Ionic Strength of the Bulk Phase. Liquids 2021, 1, 1-24. https://0-doi-org.brum.beds.ac.uk/10.3390/liquids1010001

AMA Style

Mchedlov-Petrossyan NO, Vodolazkaya NA. Protolytic Equilibria in Organized Solutions: Ionization and Tautomerism of Fluorescein Dyes and Related Indicators in Cetyltrimethylammonium Chloride Micellar Solutions at High Ionic Strength of the Bulk Phase. Liquids. 2021; 1(1):1-24. https://0-doi-org.brum.beds.ac.uk/10.3390/liquids1010001

Chicago/Turabian Style

Mchedlov-Petrossyan, Nikolay O., and Natalya A. Vodolazkaya 2021. "Protolytic Equilibria in Organized Solutions: Ionization and Tautomerism of Fluorescein Dyes and Related Indicators in Cetyltrimethylammonium Chloride Micellar Solutions at High Ionic Strength of the Bulk Phase" Liquids 1, no. 1: 1-24. https://0-doi-org.brum.beds.ac.uk/10.3390/liquids1010001

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