Sergey Eltsov

Followers

Following

Co-author

Public Views

Uploads

Papers by Sergey Eltsov

Kinetics of alkaline fading of methyl violet in micellar solutions of surfactants: Comparing Piszkiewicz's, Berezin's, and pseudophase ion-exchange models

International Journal of Chemical Kinetics, 2018

The micellar effect of surfactants of various types on the rate of the reaction between methyl vi... more The micellar effect of surfactants of various types on the rate of the reaction between methyl violet and hydroxide ion is studied. The absorption spectra show that the cation of methyl violet is bound by micelles of all types at proper concentrations of surfactants. The observed rate constant in micellar systems containing nonionic Brij-35, zwitterionic 3-(dimethyldodecylammonio)-propanesulfonate, cationic cetyltrimethylammonium bromide and hydroxide surfactants is higher, whereas in solutions of the anionic surfactant sodium dodecylsulfate is lower than that one in the surfactant-free system. Piszkiewicz's, Berezin's, and pseudophase ion-exchange models of the kinetic micellar effect are used for the treatment of the dependences of the above-mentioned constants on the surfactant concentration. The values of the corresponding kinetic parameters are compared and discussed. The influence of nonionic, zwitterionic, and anionic micelles on the reaction rate is discussed on the basis of medium and concentration kinetic effects. The character of the cationic micelles effect is somewhat paradoxical. Although the observed pseudo-first-order reaction rate constant substantially increases in the presence of such micelles, the second order-rate constant in these micelles is lower than the corresponding value in surfactant-free aqueous solution. As a possible explanation, the decrease in the reactivity of the HOions is proposed, owing to their electrostatic association with the cationic headgroups ("diverting effect").

Download

Nitrophenol Violet as a New Tool for Studying of Kinetics of Reactions in Solutions

Journal of Chemical Education, 2021

Micellar rate effects on the kinetics of nitrophenol violet anion reaction with HO– ion: Comparing Piszkiewicz's, Berezin's, and Pseudophase Ion-Exchange models

Journal of Molecular Liquids, 2018

Triphenylmethine dyes are often used as the probes for studying the properties of micellar media ... more Triphenylmethine dyes are often used as the probes for studying the properties of micellar media and other organized solutions and the influence of the latter on the kinetics of the reactions. The reports by different authors are mainly devoted to the study of the accelerated alkaline fading of cationic triphenylmethine dyes, Ct + , in micelles of cationic surfactants, whereas the presence of anionic surfactants strongly decelerates the reaction Ct + + HO-→ carbinol. At the same time, the anionic dyes interact with hydroxide ion much more slowly even in cationic surfactant micelles. For instance, as shown by Grunwald and Duynstee as early as 1959, for a sulfonephthalein dye bromophenol blue anion, BPB 2− , the reaction occurs so slowly that it is impossible to determine the rate constant. Hence, all the regularities of the nucleophilic attack of the hydroxide ion in cationic micelles were until now studied using cationic dyes. Therefore, it seemed to be significant to find an anionic triphenylmethine dye electrophilic enough to examine the rate of its reaction with alkali in the presence of cationic surfactants. As such a dye, we used another sulfonephthalein dye, nitrophenol violet, NPV (3,3′dinitrophenolsulfonephtalein), which meet the above condition. Indeed, it was possible not only to (quantitatively) describe the decelerating effect of cationic micelles on the reaction NPV 2− + HO − , but also utilize it for comparing the most popular Piszkiewicz's, Berezin's, and Pseudophase Ion-Exchange models of micellar kinetics in CTAB and CTAOH solutions. Zwitter-ionic, non-ionic, and anionic surfactants were used as well. The obtained results allow generalizing the concept of micellar effects on the kinetics of nucleophilic attack and validating the above-mentioned theories. Also, the results demonstrate the usefulness of the dye NPV for studying of the nucleophilic attack in systems with positively charged colloidal particles. For instance, in addition to the electrostatic deceleration of the reaction between two anions on lowering the polarity of the medium it was shown that the cationic head groups in the Stern layer display a "diverting" influence on the HOion.

Download

3,3′‐Dinitrophenolsulphonephthalein: an acid–base indicator dye with unusual properties

Coloration Technology, 2016

This paper is devoted to the phenolsulphonephthalein nitro derivative 3,3 0-dinitrophenolsulphone... more This paper is devoted to the phenolsulphonephthalein nitro derivative 3,3 0-dinitrophenolsulphonephthalein, also called nitrophenol violet (NPV). The neutral molecular form, H 2 R, was isolated as a sultonic tautomer, and an X-ray crystal structure analysis was carried out. UV-vis absorption spectra in methanol, DMSO, acetonitrile, and water at different pH values were ascribed to the molecular and anionic (H 2 R, HR À , and R 2À) species. Whereas the pK a values of this acid-base indicator (HR À ¡ R 2À + H +) in water and DMSO are close to those of 3,3 0 ,5,5 0-tetrabromophenolsulphonephthalein (or bromophenol blue), replacing the four Br atoms with two NO 2 groups results in a pronounced tendency to carbinol formation. In weakly acidic aqueous media, the HR À anion slowly converts into the colourless carbinol H 2 ROH À. The latter is transformed to the orange carbocation only in concentrated (70-94 wt%) sulphuric acid. The formation of H 2 ROH À is atypical for the common sulphonephthalein indicators and should be ascribed to the enhanced positive charge density on the nodal carbon atom. The reaction mechanism and kinetic equation explaining this pH-dependent process are proposed, in addition to a kinetic study of the common process R 2À + HO À ? ROH 3À in the alkaline region. The numerical characterisation of the protolytic processes obtained for NPV is also helpful in gaining a better understanding of the properties of previously studied 3,3 0 ,5,5 0-tetranitrophenolsulphonephthalein, which is much less accessible for a quantitative description.

Download

Micellar rate effects in the alkaline fading of crystal violet in the presence of various surfactants

Journal of Molecular Liquids, 2015

The influence of surfactants of various types (nonionic, cationic, anionic, and zwitterionic) on ... more The influence of surfactants of various types (nonionic, cationic, anionic, and zwitterionic) on the rate of reaction 17 of the crystal violet, cationic triphenylmethane dye, with the hydroxide ion in unbuffered aqueous solutions was 18 studied using the spectrophotometric method. It was found that the values of the rate constants increase in the 19 presence of the cationic, nonionic and zwitterionic surfactants, and decrease on the addition of the anionic sur-20 factant at concentrations both below and above the CMC. The variation of the rate constants along with the 21 change in the concentration of the surfactants may be explained on the basis of conception about distribution 22 of the reagents between aqueous and micellar phases and the changing of their properties depending on local 23 microenvironment. The character of the salt effects upon the rate constants was explained. It was revealed, 24 that the Piszkiewicz's model of micellar catalysis is inapplicable even semi-quantitatively to the most of the ex-25 amined systems.

Download

Solubility and fluorescence lifetime of 2,5-diphenyloxazole and 1,4-bis(5-phenyl-oxazolyl-2)benzene in water–ethanol and water–acetone solvent systems

Journal of Molecular Liquids, 2009

Abstract The solubility of two luminophores, 2,5-diphenyl-1,3-oxazole (PPO) and 1,4-bis(5-phenyl-... more Abstract The solubility of two luminophores, 2,5-diphenyl-1,3-oxazole (PPO) and 1,4-bis(5-phenyl-oxazolyl-2)benzene (POPOP), has been determined in water–acetone and water–ethanol solvent systems at 25.0 °C. The excited states of PPO and POPOP have been studied in these mixed solvents. The dependence of fluorescence lifetime and solubility on mixed solvents composition is discussed in terms of solvation of luminophore molecules. The multiple linear regression analysis of fluorescence lifetime and solubility dependences on solvent polarity parameters has been carried out. Equations, describing the dependence of solubility and fluorescence lifetime of luminophores on solvent parameters, are presented. It has been revealed that both solubility of PPO and POPOP and their fluorescence lifetimes are controlled mainly by the energy of cavity formation.

Revisiting tetranitrophenolsulfonephthalein

Coloration Technology, 2015

ABSTRACT Among the vast series of phenolsulfonephthalein dyes, the nitro derivatives and especial... more ABSTRACT Among the vast series of phenolsulfonephthalein dyes, the nitro derivatives and especially 3,3′,5,5′-tetranitrophenolsulfonephthalein (nitrophenol crimson) remain practically unexplored, whereas the halogen and alkyl derivatives have been studied comprehensively. This striking difference is probably due to the enormous influence of the four NO2 groups on the properties of the dye. As a result, the protolytic behaviour is unlike even that of tetrabromo phenolsulfonephthalein, and the recognised scheme of acid–base and tautomeric equilibrium of the sulfonephthaleins is unable to explain it. The molecular form H2R was isolated as a sultonic tautomer, and an X-ray crystal structure analysis was carried out. Our studies of the UV-vis absorption spectra in water, methanol, dimethyl sulfoxide, acetonitrile, acetone, and dichloromethane, as well as in aqueous micellar solutions of surfactants, allowed us to evaluate the true molar absorptivity of the dianion R2−, and to elucidate the enormous tendency to form yellow trianionic carbinol ROH3−, even in the presence of traces of H2O. Nuclear magnetic resonance and electrospray data confirm the proposed scheme of ionisation and tautomerism of nitrophenol crimson.

Solubility and fluorescence lifetime of 2,5-diphenyloxazole and 1,4-bis(5-phenyl-oxazolyl-2)benzene in water–ethanol and water–acetone solvent systems

by Sergey Eltsov and Nikolay Mchedlov-Petrossyan

Journal of Molecular Liquids, 2009

Sergey Eltsov

Uploads

Papers by Sergey Eltsov

Log In