V. N. Karazin Kharkiv National University Bulletin. Chemical series 2020-04-05T23:09:59+03:00 Alexander I. Korobov Open Journal Systems <p>Publishes papers devoted to various aspects of theoretical chemistry, chemical analysis, organic chemistry, inorganic chemistry, physical chemistry of solutions and surface phenomena, electrochemistry, materials chemistry.</p> Mechanism of enhanced oxidation ability of dilute nitric acid and dissolution of pure gold in seawater with nitric acid 2020-04-05T22:27:47+03:00 Masashi Hojo <p>It has been discovered that dilute nitric acid in reversed micelle systems can oxidize the Br<sup>-</sup> ion to Br<sub>2</sub> and we have proposed that the nitryl (or nitronium) ion NO<sub>2</sub><sup>+</sup> should be the active species in the oxidation process. Nitration of phenol in reversed micelle systems with dilute nitric acid, CHCl<sub>3</sub>/CTAC/H<sub>2</sub>O (2.0 mol dm<sup>-3</sup> HNO<sub>3</sub> in the 1.0% (v/v) H<sub>2</sub>O phase), has been performed at 35&nbsp;ºC to obtain 2- and 4-nitrophenols, where CTAC represents cetyltrimethylammonium chloride. In aqueous 2.0 mol dm<sup>-3</sup> HNO<sub>3</sub> solution accompanied by 4.0 mol dm<sup>-3</sup> LiCl (and a small amount of LiBr as the bromide resource), trans-1,4-dibromo-2-butene was successfully brominated to 1,2,3,4-tetrabromobutane. This result is good evidence that the Br<sup>-</sup> ion can be oxidized to Br<sub>2</sub> in dilute nitric acid (2.0 mol dm<sup>-3</sup>) providing it contains concentrated salts. For chloride salts, the cation effects increased as Et<sub>4</sub>N<sup>+</sup> &lt;&lt; Na<sup>+</sup> &lt; Li<sup>+</sup> &lt; Ca<sup>2+</sup> &lt; Mg<sup>2+</sup>. Even the evolution of Cl<sub>2</sub> has been demonstrated from &lt; 2.0 mol dm<sup>-3</sup> HNO<sub>3</sub> solution containing concentrated LiCl, MgCl<sub>2</sub>, and CaCl<sub>2 </sub>as well as AlCl<sub>3</sub>. The dissolution of precious metals (Au, Pt, and Pd), especially, of gold has been demonstrated in 0.1&nbsp;-&nbsp;2 mol dm<sup>-3</sup> HNO<sub>3</sub> accompanied by alkali metal, alkaline earth metal, and aluminum chlorides. The complete dissolution time of pure gold plate (20±2 mg, 0.1 mm thickness) in 2.0 mol dm<sup>-3</sup> HNO<sub>3</sub> accompanied by 1.0 mol dm<sup>-3</sup> AlCl<sub>3</sub> has been shortened remarkably with temperature increase from 15 to 80&nbsp;ºC. The dissolution rate constants, log (k /s<sup>-1</sup>), of a piece of gold wire (19.7±0.5 mg) in 20 mL of 2.0 mol dm<sup>-3</sup> HNO<sub>3</sub> accompanied by the metal chlorides, in general, increase with increasing salt concentrations at 40 and 60&nbsp;ºC. The gold can be dissolved in the solution of &lt;1.0 mol dm<sup>-3</sup> HNO<sub>3</sub> and &lt;1.0 mol dm<sup>-3</sup> HCl, i.e. a “dilute aqua regia." We have achieved a total dissolution of five pieces of the gold wire (totally 0.10 g) in 100 mL of the 1:1 mixture between seawater and 2.0 mol dm<sup>-3</sup> HNO<sub>3</sub> at ca. 100 ºC.</p> 2019-12-27T00:00:00+02:00 ##submission.copyrightStatement## Electrical conductivity, ion-molecular and interionic interactions in solutions of some tetraalkylammonium salts in acetonitrile: the influence of the ion and temperature 2020-04-05T22:27:58+03:00 Oleg N. Kalugin Elena V. Lukinova Dmytro O. Novikov <p>Conductance data for Et<sub>4</sub>NBr, Et<sub>4</sub>NBF<sub>4</sub>, Bu<sub>4</sub>NBr, Bu<sub>4</sub>NBF<sub>4</sub> in acetonitrile for the molar concentration range of 2·10<sup>-4</sup>–1·10<sup>-2</sup> mol·dm<sup>-3</sup> over the temperature range from 5 to 55 °C are reported. Limiting molar conductivities and ion association constants were determined by using the Lee-Wheaton equation for the symmetrical electrolytes. On the basis of the preliminary conductometric data analysis it was established that the closest approach parameter is almost independent from the temperature for all studied acetonitrile solutions. Therefore, the closest approach parameter was adopted as a sum of cation and anion radii for further conductometric data treatment.</p> <p>The limiting conductivities of Br<sup>-</sup>, BF<sub>4</sub><sup>-</sup>, Et<sub>4</sub>N<sup>+</sup> and Bu<sub>4</sub>N<sup>+</sup> ions and the structure-dynamic parameter of ion-molecular interaction obtained from the experimental data on limiting molar conductivities were evaluated in the framework of the approach proposed by authors [Kalugin O. N., Vjunnik I. N. Limiting ion conductance and dynamic structure of the solvent in electrolyte solution. <em>Zh. Khim. Fiz. (Rus.) </em><strong>1991,</strong> <em>10</em> 708-714]. Elongation of the alkyl radical of the tetraalkylammonium cation from Et<sub>4</sub>N<sup>+</sup> to Bu<sub>4</sub>N<sup>+</sup> leads to a significant increase in the structure-dynamic parameter, which indicates the dynamic structuring of the solvent near the tetrabutylammonium ion and increased solvophobic solvation of the Bu<sub>4</sub>N<sup>+</sup> compared to Et<sub>4</sub>N<sup>+</sup>.</p> <p>Ion association constants are discussed in terms of competition between Coulomb and non-Coulomb forces in terms of short-range square-mound potential. An increase in the ion association constants in the sequence Bu<sub>4</sub>NBF<sub>4</sub>&lt;Et<sub>4</sub>NBF<sub>4</sub>&lt;Bu<sub>4</sub>NBr&lt;Et<sub>4</sub>NBr was explained by the increase in the contribution of short-range ion-molecular interactions to the interionic attraction in addition to the electrostatic component. An increase in temperature enhances the ionic association due to both the electrostatic and short-range components.</p> 2019-12-27T00:00:00+02:00 ##submission.copyrightStatement## Force field of tetrafluoroborate anion for molecular dynamics simulation: a new approach 2020-04-05T22:28:10+03:00 Igor S. Vovchynskyi Oleg N. Kalugin <p>Design of new electrical energy storage devices including supercapacitors as well as an optimization of existing ones require not only new electrolytes, but also the deep and complete understanding of the processes occurring in the electrolyte solutions. Spectral techniques and classical molecular dynamics simulation (MDS) have gained a reputation as a reliable tool for such tasks. The starting point of any MDS is a choice or development of the force fields for all simulated particles. The combination of vibrational spectroscopy and molecular dynamics technique can provide a thorough understanding of the structure and dynamics of the ionic subsystem. In this connection, the reproduction of the vibrational spectra should be added to the requirements for the force fields of the most common electrolyte components.</p> <p>Many modern supercapacitors are based on organic electrolytes consisting of non-aqueous aprotic solvents such as acetonitrile, propylene carbonate and γ-butyrolactone and quaternary ammonium salts with tetrafluoroborate and hexafluorophosphate as anions.</p> <p>The purpose of the current work is to develop a new force field for tetrafluoroborate anion (BF<sub>4</sub><sup>-</sup>) able to reproduce not only translational diffusion in acetonitrile medium, but also the spectral properties of this ion in a condensed phase. Since found in the literature force fields of BF<sub>4</sub><sup>-</sup>, cannot satisfy these requirements, there were performed intensive quantum chemical calculations of BF<sub>4</sub><sup>-</sup> at the M06-2X/6-311++G(d,p) level of theory to construct the potential energy surface with respect to the B-F bonds and F-B-F angles followed by evaluating corresponding intramolecular potential constants. Combining the obtained bond and angle force constants with partial charges on B and F atoms calculated at the same level of theory, and literature values of Lennard-Jones parameters, a new force field model for BF<sub>4</sub><sup>-</sup> anion was created. Based on the carried out MD simulations of the BF<sub>4</sub><sup>-</sup> ion in an infinitely diluted acetonitrile solution, it was proved that the obtained resulting model is capable to reproduce both transport and intra-ion vibrational properties of the tetrafluoroborate anion.</p> 2019-12-27T00:00:00+02:00 ##submission.copyrightStatement## Interparticle interactions and dynamics in BmimBF4 and LiBF4 solutions in propylene carbonate: MD simulation 2020-04-05T22:28:20+03:00 Dmytro S. Dudariev Kate O. Logacheva Yaroslav V. Kolesnik Oleg N. Kalugin <p>Ionic liquids have gained immense popularity in recent decades due to a combination of unique properties. Despite the widespread use of ionic liquids mixtures with aprotic dipolar solvents in electrochemistry, it remains relevant to predict their macroscopic, primarily transport, properties based on the microscopic picture of the entire set of interparticle interactions in such systems. The method of molecular dynamics simulation (MDS) is one of the most powerful tools for solving problems of this kind. However, one of the unsolved problems of the classical MDS of ion-molecular systems is the correct accounting of polarization effects. Recently it was proposed to use a variation of the effective ion charges in solutions to solve this task.</p> <p>This paper presents the results of the MDS structural and dynamic properties of 1-butyl-3-methylimidazolium (BmimBF<sub>4</sub>) and lithium (LiBF<sub>4</sub>) tetrafluoroborates solutions in propylene carbonate (PC) at 298.15 K in <em>NPT</em> ensemble using GROMACS and MDNAES software packages.</p> <p>The possibility of reproducing the experimental dynamic properties (diffusion coefficients of cations and solvent, viscosity, and electrical conductivity) of binary systems based on mixtures of ionic liquids with PC in a wide concentration range was shown. Polarization effects were taken into account by reducing the partial charges of the ion atoms.</p> <p>The structure of the solvation shell of cations was studied within the framework of radial distribution functions, distribution of coordination numbers and the presence of hydrogen bonds between the organic cation and solvent molecules. The results point to stronger and more structured solvation shell of the Li<sup>+</sup> cation compared to Bmim<sup>+</sup>, which is consistent with the conclusions about the mobility of these cations. The reorientation times of propylene carbonate molecules and their lifetimes in the framework of the first solvation shells of the cations are several times higher for the lithium cation.</p> 2019-12-27T00:00:00+02:00 ##submission.copyrightStatement## Aqueous solution of poly (hexamethylene guanidine hydrochloride) and poly (diethylenamine guanidine hydrochloride) as studied with acid-base indicators 2020-04-05T22:28:31+03:00 Anastasia Yu. Kharchenko Maria A. Romakh Karolina V. Yanova Marina N. Tereshchuk Nikolay O. Mchedlov-Petrossyan <p>In this paper, the properties of cationic polyelectrolytes as tools for governing the protolytic equilibrium of acid-base indicators in water were examined. For this purpose, water-soluble and pH-dependent poly (hexamethylene guanidine hydrochloride), PHMG, and poly (diethylenamine guanidine hydrochloride), PDEG, were studied. As molecular probes, a set of anionic indicator dyes were used; the key parameter is the so-called apparent ionization constant, <em>K<sub>a</sub><sup>app</sup></em>. The electrokinetic potential of the above polycationic species in the acidic pH region is substantially positive. As a rule, the polyelectrolytes display marked influence on the absorption spectra and state of the acid-base equilibrium of the anionic dyes at pH &lt; 7, especially in the case of PHMG. Both effects resemble those known for the same dyes in aqueous solutions of cationic surfactants but are less expressed. Normally, the acid-base equilibria were studied at polyelectrolyte : dye ratio of 150 : 1, at ionic strength 0.05 M, and 25 <sup>o</sup>C. The decrease in the p<em>K<sub>a</sub><sup>app</sup></em> (≡ –log<em>K<sub>a</sub><sup>app</sup></em>) value on going from water to the PHMG solution is most expressed for bromocresol green (<em>HB<sup>–</sup></em> ↔ <em>B<sup>2–</sup> + H<sup>+</sup></em>): p<em>K<sub>a,2</sub><sup>app</sup></em>&nbsp;–&nbsp;p<em>K<sub>a,2</sub><sup>w</sup></em>&nbsp;=&nbsp;–1.93. For bromophenol blue, bromocresol purple, and sulfonefluorescein, the shift of the equilibrium is less expressed. Some kinds of specific interactions with the polyelectrolytes were revealed for methyl orange and bromophenol blue. Also, the dependence of p<em>K<sub>a</sub><sup>app</sup></em> on logarithm of ionic strength allows estimating the degree of counterion binding by the polycation: <em>β</em> = 0.40.1.</p> 2019-12-27T00:00:00+02:00 ##submission.copyrightStatement## Behavior of fullerene C70 in binary organic solvent mixtures as studied using UV-Vis spectra and dynamic light scattering 2020-04-05T23:09:59+03:00 Nikita A. Marfunin Nikolay O. Mchedlov-Petrossyan <p>In this paper, the formation of colloidal species of fullerene C<sub>70</sub> in organic solvents was studied. The examining of the UV-visible spectra was accompanied by particle size analysis using dynamic light scattering, DLS. Stock solutions of C<sub>70</sub> in non-polar toluene and <em>n</em>-hexane were diluted with polar solvents acetonitrile and methanol. The appearance of colloidal species with a size within the range of ≈50–500 nm is accompanied by alterations of the absorption spectra.</p> <p>In the toluene–acetonitrile and toluene–methanol binary mixed solvents at 25 <sup>o</sup>C, the absorption spectra of C<sub>70</sub> (5×10<sup>–6</sup> M) tend to retain the features of the spectrum in neat aromatic solvent even if the C<sub>70</sub> molecules are gathered into colloidal aggregates. Earlier such phenomenon was observed for C<sub>60</sub> in benzene–acetonitrile and toluene–methanol solvent systems. This gives support to the idea of rather stable primary solvate shells formed by aromatic molecules around the fullerene molecules. The behavior of C<sub>70</sub> in toluene mixtures with methanol was compared with the earlier reported results from this laboratory for the C<sub>60</sub> fullerene in the same solvent system.</p> <p>The study of <em>n</em>-hexane–methanol mixtures was performed at elevated temperature because of limited miscibility of these solvents at 25 <sup>o</sup>C. Accordingly, the C<sub>70</sub>–toluene–methanol system was also examined at 40 <sup>o</sup>C. A small but distinctly noticeable difference was revealed. Whereas in the case of the last-named system, the absorption spectrum typical for molecular form of C<sub>70</sub> is still observable when colloidal species are already present in the solution, the turning-point between molecules and colloids as determined by both UV-visible spectra and DLS coincides for the <em>n</em>-hexane–methanol binary mixed solvent. Hence, the solvation shells formed by the aliphatic solvent around C<sub>70</sub> are less stable as compared with those formed by toluene.</p> <p>Finally, the absorption spectra of C<sub>70</sub> in the mixed solvents toluene–<em>n</em>-hexane were analyzed. These data give some support to the assumption of preferable solvation of the C<sub>70</sub> molecules by the aromatic co-solvent.</p> 2019-12-27T00:00:00+02:00 ##submission.copyrightStatement##