Yu. E. Zevatskii

Conthemporary methods for the experimental determination of dissociation constants of organic acids in solutions

The survey is dedicated to the critical analysis of different experimental methods of determining the dissociation constants (Ka) of organic acids in solutions. Advantages and disadvantages of the contemporary methods of rapid analysis used in biochemistry are considered. Special attention is paid to the problems of measurements in the nonaqueous media and to the reasons for possible incorrect results. The processes in solutions that should be taken into account for obtaining the correct values of dissociation constant are analyzed. On the basis of the consideration the recommendations directed toward an increase in the accuracy of measurements are given.

Tetrazoles with oxygen-, sulfur-, and selenium-containing substituents

The data on the synthesis, properties, reactions, and practical application of tetrazoles with oxygen-, sulfur-, and selenium-containing substituents are systematized. Comparative analysis of structure and reactivity was carried out for the compounds under consideration.

Dependence of the protonation constants of organic compounds on their molecular volume

An approach has been developed, which establishes a linear correlation between molecular parameters of organic compounds with account taken of atomic contributions. Relations between the energy of protonation of 395 organic compounds divided into four groups and their molecular volume were drawn. The differences between the experimental and calculated values within each group did not exceed 4%.

Limit of concentration constant of protolytic equilibrium

its thermodynamic equilibrium constant being expressed in terms of activities of the reactants: Ka = аА–аН+/aНА. Generally, experimental methods allow determining either the concentration constant Ka expressed via the equilibrium concentrations of the reactants or the apparent constant Ka expressed via the lyonium ion activity аН+ and equilibrium concentrations of other reactants. In order to recalculate the thermodynamic constant from Ka or Ka, various approximations and corrections related to ionic strength are used (the Debye–Hückel equation, the Davies equation, the Stokes–Robinson equation, etc) [1–3]. The solution is normally considered close to the ideal one at low ionic strength (I < 0.01 mol/L), and the intermolecular interactions are neglected for [1, 4]. In such a case, the activity coefficients of the ionic species are close to unity, and hence Ka = Ka. Analysis of the referenced values of thermodynamic dissociation constants of weak acids and bases, including biologically important organic compounds, revealed that in some cases significantly different values have been reported as determined independently by different research groups [5, 6].

Kinetic studies of the copper-catalyzed cross-coupling of 1-phenyltetrazole-5-thiol and iodobenzene

Kinetics of the copper-catalyzed cross-coupling of 1-phenyltetrazole-5-thiol and iodobenzene under thermal and dielectric heating has been studied; the kinetic parameters of the reaction have been calculated. Microwave irradiation has not influenced significantly the reaction molecular mechanism; the process acceleration can be due to macrokinetic effects.

Protolytic equilibria of picric acid in a mixture of protophobic and protophilic polar solvents non-donors of H-bonds

A new differentiating medium for the study of prototropic equilibria is proposed: acetonitrile with a small addition of DMSO. From the dependence of the picric acid pKa on the content of DMSO in this medium the optimum composition of the mixture was found ensuring the stability of the pKa values with minimal addition of DSMO: 4 wt %. It was experimentally confirmed that the addition of water in an amount up to 0.1 wt % has virtually no effect on the measured pKa value in a mixture with the optimum composition.

Calculations of Dissociation Constants of Carboxylic Acids by Empirical and Quantum-Chemical DFT Methods

Dissociation constants of 15 carboxylic acids in water, methanol, and DMSO were calculated by empirical and quantum-chemical DFT methods. The maximal error of the empirical calculation was 1.4%. A comparative analysis of the results obtained was carried out.

Mechanism of the zinc-catalyzed addition of azide ion to unsaturated compounds: Synthesis of 5-substituted 1 Н -tetrazoles from nitriles and of 1-substituted 1 Н -tetrazole-5-thiols from isothiocyanates

The mechanism of the formation of 5-substituted 1H-tetrazoles from organic nitriles and thiocyanates in the presence of NaN3 and ZnCl2 in aliphatic alcohols was studied. The results of this study allowed efficient methods of synthesis of substituted tetrazoles from nitriles, thiocyanates, and isothiocyanates to be proposed.

Synthesis of 2-Substituted Tetrazole-5-Thiols and 5,5'-Disulfandiylbis(2-Alkyl-2H-Tetrazoles)

A method has been proposed for the synthesis of 2-alkyltetrazole-5-thiols. It was shown that these compounds are readily oxidized to the corresponding disulfides and their further functionalization has been studied.

Algorithm for calculating the dissociation constants of weak electrolytes and ampholites in water solutions

An algorithm for calculating the dissociation constants of weak organic acids and bases in water solutions is developed on the basis of spectrophotometric data on the UV and visible regions without measuring the рН of the medium or using buffer solutions. The proposed algorithm is tested experimentally for six single-base acids and single-acid bases of different strengths. The relative error in determining the dissociation constants does not exceed 5% and is in agreement with the literature data.