Sigmatropic mechanism of the chlorotropic isomerization of phosphazopentachloroethane

The sigmatropic and dissociative-recombination mechanisms of the chlorotropic isomerization of benzodioxachlorophosphazopentachloroethane and its 1:2 solvate with chloroform have been studied by the MNDO-PM3 method in the supermolecular approximation. It is observed that the thermodynamically more stable chlorotropic isomer corresponds to the phosphorane structure with axial-equatorial disposition of two chlorine atoms and the two oxygen atoms in the dioxaphosphole ring, in complete agreement with literature data on teh³⁵Cl NQR spectrum. It is shown that the most likely pathway for phosphorus-carbon chlorotropic rearrangement for both phosphazopentachloroethane and its solvate with two molecules of chloroform is the sigmatropic route. Institute of Bioorganic and Oil Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 02094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 177–181, May–June, 2000.     

The chlorotropic isomerization mechanism for amidinium tetrachlorophosphorates

MNDO-PM3 quantum-chemical calculations have been combined with³⁵Cl NQR spectroscopy in research on the thermodynamic and kinetic stability of chlorotropic isomers in the Cl₄P(NCH₃)₂CR amidinium tetrachlorophosphorate series, in which R=C₆H₅, CCl₃, CF₃, Cl; the relative thermodynamic stability of the phosphorate P^VI isomer is higher than that of the phosphetidine P^V one and has a minimum in the series for the CF₃ derivative. The chlorotropic P→C transformation of the isomeric forms of the amidinium tetrachlorophosphorates occurs in liquid solutions and in melts by an intramolecular sigmatropic mechanism, not by the formation of a contact ion pair. Institute of Bioorganic Chemistry and Petroleum Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 155–161, May–June, 1999.     

Peculiarities of the mechanism of chlorotropic and conformational isomerism in a series of chloromethyl isocyanates

The thermodynamic and kinetic stability of chlorotropic isomers in a series of chloromethyl isocyanates Cl_3−nH_nC−N=C=O, where n=0, 1, 2, has been shown by quantum chemical calculations, using the MNDO method, and by³⁵Cl NQR spectroscopy. The phase transformations of two polymorphic modifications of N-chlorocarbonyl dichloride, which is a stable iminocarbonyl form of trichloromethyl isocyanate with small conformational activation barriers, have been studied. Institute of Bioorganic and Petrochemistry, National Academy of Sciences of Ukraine, 1 Murmansk ul., Kiev-94 252660, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 164–169, May–June, 1998.     

Role of dimethylformamide in generating the active form of platinum for catalyzing the synthesis of diaryls from aryl iodides

A mechanism is proposed for the reaction of aryl iodides with platinum(II) tetrachloride complexes in dimethylformamide including formation of PtCl₃(CONMe₂)²⁻ in the first step through activation of a dimethylformamide C−H bond by platinum(II) and subsequent oxidative addition of ArI to this species. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 244–246, July–August, 1998.     

Active intermediates in the oxidative bromochlorination of olefins in concentrated hydrochloric acid

A study was carried out on the oxidative bromochlorination of olefins in the presence of KBr using hydrogen peroxide and an electrochemical technique. Asymmetric trihalide anions, Br₂Cl⁻ and BrCl₂ ⁻, were found to be the active bromochlorination reagents. The reaction mechanism was discussed. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya St., 253660 Kiev-94. Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 248–251, July–August, 1997.     

Kinetics, substrate selectivity and mechanisms of the first step in the oxidation of alkylbenzenes in the HVO3−H2SO4 system

The kinetics, kinetic isotope effects, and substrate selectivity were studied for the oxidation of alkylbenzenes in the HVO₃−H₂SO₄ system at 30°C. The reaction proceeds by an electrophilic substitution mechanism through a slow step involving formation of a charge transfer complex between the arene and VO ₂ ⁺ cation and is similar to nitration by the NO ₂ ⁺ cation. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 6, pp. 349–353, November–December, 1999.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

Rate constants for the formation and decomposition of the σ-adduct in the reactions of N-arylpyridinium salts

The rate constants for the formation (k₁) and decomposition (k ₋₁ ,k ₂ ,k ₃ ) of the σ-adduct were determined for the reactions of 4-R-N-(2,4-dinitrophenyl)pyridinium salts [R=Py, CON(C₂H₅)₂] with 4-methoxyaniline, which takes place by the ANRORC substitution mechanism. L. M. Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 282–285, September–October, 1998.     

Basic structural types of binary niobates and tantalates with 1∶3 stoichiometry of cations. Variants of cation arrangements in planar nets

For planar (two-dimensional) unit cells containing 4 and 8 nodes, we have found 3 and 19 variants of arrangements of two cation types with 1∶3 stoichiometry in the 3⁶ net, respectively, and suggested notation for these variants. Virtually all structures analyzed have either an F- or I-complex of close-packed cation planes and the corresponding cation sublattices. In La₂ThTaO₆Cl₃, the Cl⁻ anion occupies some sites of the cation sublattice. The cation sublattices La₃NbO₇ (weberite structural type) and Sm₂ScTaO₇=Sm₂(Se, Ta)₂O₇ (pyrochlore) have 4⁴ nets with identical or different cation packings, which alternate in the structures. In some structures with 1∶1 general stoichiometry of cations (e.g., Na₂Ta₂O₅F₂), we observe alternation of the 6⁶ dense nets having 1∶3 and 3∶1 stoichiometries Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Institute of Crystallography, Russian Academy of Sciences, Translated fronZhumal Struktumoi Khimii, Vol. 36, No. 1, pp. 128–137, January–February, 1995. Translated by T. Yudanova     

Indirect electrochemical reductive degradation of polycarbonates

We have studied the kinetic characteristics of degradation of polycarbonates with different structures in dimethylformamide when treated with the products of electrochemical reduction of a (C₄H₉)₄NClO₄ solution in dimethylformamide (supporting solution). We have shown that this process (which can be described as indirect electrochemical reductive degradation) occurs according to a nucleophilic catalytic mechanism. Institute of Bioorganic Chemistry and Petroleum Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 319–323, September–October, 1998.     

Kinetics and mechanism of the oxidation of arenes in the presence of heteropoly acids and palladium(II) complexes supported on silica gel

Pd(II) complexes and twelfth-series heteropoly acids (HPA) H₉[PMo₆V₆O₄₀] and H₃[PMo₁₂O₄₀] supported on silica gel oxidize benzene and toluene at 95°C. The formation of methyldiphenylmethane in the oxidation of toluene on HPA/SiO₂ and (PdCl₂−HPA)/SiO₂ catalysts, KIE>1 for the toluene/toluene-d₈ pair, and greater rate for toluene than for benzene are in accord with a one-electron transfer mechanism. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 249–252, July–August, 1999.     

HPLC separations of meropenem and selected pharmaceuticals using a polar endcapped octadecylsilane narrow bore column

Summary Stability indicating high performance liquid chromatography methods have been developed for the assay of meropenem in combination with either dopamine (A), aminophylline (B), metoclopramide (C) or ranitidine (D) in intravenous fluid mixtures. Separations B, C and D were performed on a polar endcapped ODS column (150×2 mm) with aqueous, pH 3.0—acetonitrile (89∶11, 88∶12, and 92∶8) eluent and detection at 270, 290, 317 nm respectively. Meropenem was linear over the concentration ranges 126.88–507.50, 131.25–525, and 131.25–525 gmg mL⁻¹. Aminophylline, metoclopramide and ranitidine were linear over the concentration ranges 13–52, 37.5–150, and 25–100 μg mL⁻¹. Separation A was performed on a conventional ODS column (150×2.1 mm) with aqueous, pH 3.0—acetonitrile (85∶15) eluent and detection at 280 nm. Meropenem and dopamine were linear in the 61.25–245 and 10–40 μg mL⁻¹ ranges, respectively. Accuracy and precision for all methods were 0.20–3.30% and 0.10–1.58%, respectively. Accelerated stability studies have been carried out on each drug by exposure to acid, base, H₂O₂, and heat for different time periods.     

Electrochemically activated insertion of fluoroalkyl groups into organic and inorganic substrates

This article summarizes and correlates information on electrochemical processes of fluoroalkylation of organic and inorganic compounds, based on cathodic and anodic activation of fluoroalkyl halides R_FHal. The electrochemical behavior of R_FHal under various conditions is examined, as well as the interaction of fluoroalkyl radicals, generated in cathodic reduction of R_FHal, with various nucleophiles (thiophenolates, phenolates, anionic nitrogen-containing heterocycles, their methylene bases, etc.); with ethylenic, acetylenic, and carbonyl compounds; and with “small” molecules (CO₂, O₂, SO₂, CS₂). Possible mechanisms of such processes are examined critically, along with prospects for further development of this new direction in research. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospect Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 17–34, January–February, 1999.     

Stochastic resonance in the oxidation of nadh by atmospheric oxygen in the presence of copper(II) aqua ions in a constant-agitation flow-type reactor

The oxidation of NADH by atmospheric oxygen in the presence of copper(II) aqua ions in a constant-agitation flow-type reactor was investigated. During the experiments the initial concentrations of the reagents ([NADH]₀, [Cu²⁺]₀) and their delivery rate (k₀) were varied. It was established that there are four reaction regimes in the system: steady state (SS); low-amplitude periodic autooscillation (εR); high-amplitude periodic (SR₁) and aperiodic (SR₂) autooscillations. The three-dimensional region of existence for these regimes was constructed in the coordinates [NADH]₀, [Cu²⁺]₀, and k₀. It was shown by statistical analysis that oscillations of the SR₁ and SR₂ types are due to stochastic resonance. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 03039, Ukraine. Translated from Teoreticheskaya i éksperimental'aaya Khimiya, Vol. 36, No. 2, pp. 95–100, March–April, 2000.     

Factors determining selectivity of ethylene conversion to butadiene over aluminosilicate catalyst

A study has been made of the influence of temperature, partial pressure of C₂H₄, and contact time on the selectivity of direct conversion of ethylene to butadiene over an aluminosilicate catalyst. A critical analysis has been made of the competing directions of C₂H₄ conversion, which determine the selectivity of C₄H₆ formation under conditions of a heterogeneous-homogeneous mechanism in carrying out the process. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 78–82, March–April, 1997.     

Separation of C1–C4 hydrocarbon gases on impregnated liquid membranes

Diffusion plays an important role along with complexation in the separation of C₁–C₄ hydrocarbon gases on copper-containing impregnated liquid membranes. The partition factor changes as the process goes from nonsteady-state to steady-state. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 191–195, May–June, 1998.     

Formation of nanoperiodic structures based on keggin and lacunar anions of phosphotungstic acid and cationic surfactants

Surface-active cations (A⁺) in an aqueous medium, at pH 1.0 with excess phosphotungstic acid, form compounds with the composition A₃[PW₁₂O₄₀]; but at pH 4.5, they form acid salts A_nH_7−n[PW₁₁O₃₉]·xH₂O that have a nanoperiodic structure. The structural parameters are greatly dependent on the nature of the surfactant and on the type of heteropolyion. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospect Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 250–256, July–August, 1998.     

Microcalorimetric Study of the Oscillating Extraction System

The power–time curves of the oscillating extraction system were determined at different temperatures for the extraction of hydrochloric acid and acetic acid with primary amine N₁₉₂₃ (R–CH(NH₂)–R¹), R, R ¹ represent alkyl of C_9–11 in chloroform using the titration microcalorimetric method. The apparent activation energy was calculated from the induction period (t _in), the first oscillation period (t ^p.1) and the second oscillation period (t _p.2). This revised version was published online in August 2006 with corrections to the Cover Date.     

Reactivity of inorganic α-nucleophiles in the transfer of phosphoryl and phosphonyl groups

The kinetic behavior of inorganic α-nucleophiles (NH₂O⁻, HOO⁻, ClO⁻, BrO⁻, and F⁻ ions) in the transfer of phosphoryl and phosphonyl groups was studied. It was shown that ClO⁻ and BrO⁻ ions are unique α-nucleophiles, exhibiting not only supernucleophilic characteristics but also high oxidizing activity. The undoubted leaders among inorganic nucleophiles are the HOO⁻ ion and hydroxylamine. The latter cleaves substrates that are stable in water unusually quickly not only in alkaline but also in neutral and acidic media. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 83114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 4, pp. 226–232, July–August, 2000.     

Interaction of immobilized 2,8,14,20-tetramethyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene with Na+, Cs+, and NH4 + ions and organic cations

The equilibrium in the system water—electrolyte—cross-linked polymer containing immobilized 2,8,14,20-tetramethyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene was studied. Immobilized calixarene 1 was shown to form 1∶1, 1∶2, 1∶3, and 1∶4 compounds with inorganic cations (Na⁺, Cs⁺, and NH₄ ⁺), and with organic cations (hexamethylen-tetramine and β-diethylaminoethylp-aminobenzoate) 1∶1 compounds are formed. The affinity of immobilized calixarene1 increases in the series of cations: hexamethylenetetramine <Na⁺, Cs⁺, NH₄ ⁺<β-diethylaminoethylp-aminobenzoate. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2214–2216, November, 1998.