Showing papers in "Russian Chemical Bulletin in 2003"
TL;DR: In this paper, a review of nitrogen fixation in solution is presented, where the optimum catalyst is the polynuclear complex, and the limiting step involves the electron transfer from a reducing agent.
Abstract: Reports on nitrogen fixation in solution are reviewed. The optimum catalyst is the polynuclear complex. The reaction proceeds as a multielectron process, and the limiting step involves the electron transfer from a reducing agent.
202 citations
TL;DR: In this paper, side self-oxidation of thiols was studied and it was found that these reactions in neutral and alkaline solutions are induced by impurities of variable-valence metals.
Abstract: Side self-oxidation of thiols was studied. It was found that these reactions in neutral and alkaline solutions are induced by impurities of variable-valence metals. The ability of transition metals to catalyze oxidation of thiols changes in the order Cu > Mn > Fe > Ni ≫ Co. The plot of the self-oxidation rate vs. pH passes through a maximum whose position on the pH scale depends on both the nature of metal and the structure of the thiol oxidized. For thiols having different structures, the kinetic orders in reactions catalyzed by copper ions differently vary with pH, which is apparently associated with the formation of complexes possessing different catalytic activity.
149 citations
TL;DR: In this article, the synthesis and structures of a new class of supramolecular compounds composed of macrocyclic cavit and cucurbituril and molybdenum or tungsten chalcogenide clusters are surveyed.
Abstract: The review surveys the synthesis and structures of a new class of supramolecular compounds composed of the macrocyclic cavitand cucurbituril and molybdenum or tungsten chalcogenide clusters. The structural motifs of supramolecular compounds and factors influencing their formation are considered.
74 citations
TL;DR: In this paper, the influence of doping with various impurities (Pt, Pd, Ru, Rh, Cu, Ni, or Fe) on the composition, microstructure, and sensor properties of nanocrystalline SnO2 was discussed.
Abstract: The review surveys studies aimed at constructing new materials for gas sensors based on nanocrystalline tin dioxide. The influence of doping with various impurities (Pt, Pd, Ru, Rh, Cu, Ni, or Fe) on the composition, microstructure, and electrophysical and sensor properties of nanocrystalline SnO2 was discussed. The conditions for the preparation of powders and thick and thin SnO2 films by the wet chemical method and aerosol pyrolysis of organometallic compounds are reported. The mechanism of interaction of pure and doped nanocrystalline SnO2 with a gas phase was analyzed based on the data from Mossbauer, Auger electron, and X-ray photoelectron spectroscopy and the results of in situ Raman spectroscopy, XANES, and conductivity measurements.
65 citations
TL;DR: In this article, the results of X-ray diffraction studies of large stoichiometric transition metal clusters containing from 20 to 145 atoms in metal cores surrounded by ligand shells (72 compounds) are surveyed.
Abstract: The present review surveys the results of X-ray diffraction studies of large stoichiometric transition metal clusters containing from 20 to 145 atoms in metal cores surrounded by ligand shells (72 compounds). Structures of such clusters have fragments of close packings (face-centered cubic (f.c.c.), hexagonal close (h.c.p.), and body-centered cubic (b.c.c.) packings) characteristic of crystalline bulk metals as well as mixed packings (f.c.c./h.c.p.), local close packings with pentagonal symmetry, and strongly distorted “amorphous” packings. The observed packing types, their distortions, and the relationship between the atomic structures of metal cores and the atomic radial distribution functions (RDF) are discussed. The structural principles established for the large clusters are applied to analysis of the experimental RDF for metal nanoparticles determined by X-ray diffraction and EXAFS spectroscopy.
55 citations
TL;DR: In this paper, the products of thermal transformation of substituted N-aryl-o-quinoneimines were studied using NMR spectroscopy, and the formation of 4aH-phenoxazine, which was further dimerized by the Diels-Alder reaction, was established.
Abstract: Products of thermal transformation of substituted N-aryl-o-quinoneimines were studied using NMR spectroscopy. The formation of 4aH-phenoxazine, which was further dimerized by the Diels—Alder reaction, was established.
53 citations
TL;DR: In this article, the catalytic and complexing properties of two perfluorinated polymercuramacrocycles, viz., cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 and cyclic pentameric polycyclic perfluorsopropylidenmercury [(CF3)2CHg]5, are analyzed.
Abstract: The catalytic and complexing properties of two perfluorinated polymercuramacrocycles, viz., cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 and cyclic pentameric perfluoroisopropylidenemercury [(CF3)2CHg]5, are analyzed. These macrocycles contain several Lewis acidic centers in the ring and can be considered as peculiar antipodes of crown ethers and their thia and aza analogs. Both macrocycles can efficiently bind various anions to form unique complexes, in which the anionic species is simultaneously coordinated to all Lewis acidic atoms of the ring. For the (o-C6F4Hg)3 macrocycle, unusual complexes with various neutral Lewis bases, such as nitriles, carbonyl compounds, aromatic hydrocarbons, etc., were also described. Data on the activity of polymercury-containing macrocycles in phase transfer catalysis of electrophilic reactions and proton transfer from an aqueous to an organic phase are surveyed and discussed.
46 citations
TL;DR: In this paper, the molecular and crystal structure of 2-amino-3-(2-methoxyethoxycarbonyl)-4-(2 -nitrophenyl)-5-oxo-5,6,7,8-tetrahydro-4H-benzo[b]pyran was established by X-ray diffraction analysis.
Abstract: Substituted 2-aminobenzo[b]pyrans were synthesized by three-component condensation of aromatic aldehydes, cyanoacetic acid derivatives, and cyclic 1,3-diketones. The molecular and crystal structure of 2-amino-3-(2-methoxyethoxycarbonyl)-4-(2-nitrophenyl)-5-oxo-5,6,7,8-tetrahydro-4H-benzo[b]pyran was established by X-ray diffraction analysis.
44 citations
TL;DR: In this paper, experimental data on the structures of aqueous electrolyte solutions under ambient conditions are considered, and the hydrated metal complexes formed in the solutions are described systematically depending on the size of the cation, the charge and the structure of the outer electron shell.
Abstract: Published and authors" experimental data on the structures of aqueous electrolyte solutions under ambient conditions are considered. The hydrated metal complexes formed in aqueous solutions are described systematically depending on the size of the cation, the charge, and the structure of the outer electron shell.
43 citations
TL;DR: In this paper, the authors studied the capacity of CO2 in the presence of water vapor by the K2CO3 −γ-Al2O3 composite sorbent and showed that the capacity decreases during the first 10 regeneration cycles due to the formation of an inactive phase of potassium aluminum carbonate.
Abstract: Sorption of CO2 in the presence of water vapor by the K2CO3—γ-Al2O3 composite sorbent was studied by IR spectroscopy in situ, X-ray diffraction analysis, and the differentiating dissolution method and reasons for a decrease in its dynamic capacity are given. The samples containing K2CO3·1.5H2O in pores are characterized by the maximal dynamic capacity. A mechanism for CO2 sorption was proposed, which qualitatively explains the obtained dependence of the capacity on the water content in the composite sorbent. A high dynamic capacity can be maintained by regeneration of the sorbents by water vapor at 170 °N. The capacity of the sorbents decreases during the first 10 sorption—regeneration cycles due to the formation of an inactive phase of potassium aluminum carbonate.
40 citations
TL;DR: The first synthesis of 7-substituted 6-ethoxycarbonyl-5-methyl-4,7-dihydroazolo[1,5-a]pyrimidines was carried out for the first time by the reactions of aminoazoles (3-aminopyrazole, 3-amino-1,2,4-triazole, or 5-aminotetrazole) with acetoacetic ester and aliphatic, aromatic, or heteroaromatic aldehyde as discussed by the authors.
Abstract: The three-component synthesis of 7-substituted 6-ethoxycarbonyl-5-methyl-4,7-dihydroazolo[1,5-a]pyrimidines was carried out for the first time by the reactions of aminoazoles (3-aminopyrazole, 3-amino-1,2,4-triazole, or 5-aminotetrazole) with acetoacetic ester and aliphatic, aromatic, or heteroaromatic aldehyde.
TL;DR: In this article, a convenient preparative method was developed for the synthesis of 4-amino-3-furoxancarboxylic acid azide, which is a universal synthon for the preparation of functional furoxan derivatives.
Abstract: A convenient preparative method was developed for the synthesis of 4-amino-3-furoxancarboxylic acid azide, which is a universal synthon for the preparation of functional furoxan derivatives. This method was used for preparing new azo-, azoxy-, azido-, cyano-, nitro-, carbonylamino-, and hydroxylamino-substituted furoxan derivatives, which have earlier been difficultly accessible.
TL;DR: In this paper, the influence of aryl, heterocyclic, amide, alkyl, alkoxyl, thioalkoxyl and ferrocenyl substituents at the phosphorus atom on its electron-donating ability was studied by the measurement of direct 31P-77Se spin-spin coupling constants for the corresponding selenides.
Abstract: The influence of aryl, heterocyclic, amide, alkyl, alkoxyl, thioalkoxyl, and ferrocenyl substituents at the phosphorus atom on its electron-donating ability was studied by the measurement of direct 31P—77Se spin-spin coupling constants for the corresponding selenides. Series of diphenylorganylphosphines and their selenides were studied.
TL;DR: In this paper, X-ray diffraction analysis demonstrated that the metal atoms in these complexes are bound to the portal oxygen atoms of cucurbituril molecules via hydrogen bonds.
Abstract: Slow evaporation of solutions of samarium nitrate and thorium chloride in hydrochloric acid containing the macrocyclic cavitand cucurbituril (C36H36N24O12) afforded crystals of the [{Sm(H2O)5(NO3)}2(C36H36N24O12)](NO3)4·6.5H2O and [{Th(H2O)5Cl}2(C36H36N24O12)]Cl6·13H2O complexes, respectively. The [Sm(C36H36N24O12)(H2O)5(SO4)][Sm(H2O)5(SO4)2]·17H2O complex was generated upon heating (130 °C) of a mixture of samarium sulfate, cucurbituril, and water in a sealed tube. X-ray diffraction analysis demonstrated that the metal atoms in these complexes are bound to the portal oxygen atoms of the cucurbituril molecules. In addition, the portal oxygen atoms of cucurbituril are linked to the coordinated H2O molecules via hydrogen bonds.
TL;DR: In this paper, the key factors influencing the Diels-Alder reaction rate at ambient and elevated pressures were elucidated using data on the reactivity of various diene-dienophile systems in usual and Lewis acid-catalyzed Diels Alder reactions, the reaction enthalpy, complex formation, dissolution and solvation, and the donor-acceptor properties of the reactants.
Abstract: The key factors influencing the Diels—Alder reaction rate at ambient and elevated pressures were elucidated using data on the reactivity of various diene—dienophile systems in usual and Lewis acid-catalyzed Diels—Alder reactions, the reaction enthalpy, complex formation, dissolution, and solvation, and the donor-acceptor properties of the reactants. It was found that taking account of both the orbital interaction energy and the balance of bond rupture and formation energies allows correct prediction of the reaction rate in the absence or in the presence of Lewis acids.
TL;DR: In this article, the crystal structures of these supramolecular compounds are built from polymeric chains, which consist of the alternating cucurbit[n]uril molecules and Sr2+ cations linked through the bridging aqua ligands and nitrate anions.
Abstract: Crystals of the {[Sr4(H2O)12(NO3)4](C36H36N24O12)}(NO3)4·3H2O and {[Sr2(H2O)12][Sr(H2O)3(NO3)2]2(C48H48N32O16)}(NO3)4·8H2O were prepared by slow concentration of aqueous solutions containing strontium nitrate and macrocyclic cavitands, viz., cucurbit[6]uril and cucurbit[8]uril ([C6H6N4O2]
n
, n = 6 and 8), respectively. According to the results of X-ray diffraction analysis, the crystal structures of these supramolecular compounds are built from polymeric chains, which consist of the alternating cucurbit[n]uril molecules and Sr2+ cations linked through the bridging aqua ligands and nitrate anions. The supramolecular compound of cucurbit[8]uril provides the first example of compounds in which this macrocycle is bound to metal aqua complexes.
TL;DR: In this paper, magnetic measurements and X-ray diffraction study confirmed the trivalent state of the ytterbium atom and the radical nature of the DAD ligand in complex 1.
Abstract: Oxidation of (C5Me5)2Yb(THF)2 with diazabutadiene ButN=CHCH=NBut (DAD) afforded the (C5Me5)2Yb(ButNCHCHNBut) complex (1). The magnetic measurements and X-ray diffraction study confirmed the trivalent state of the ytterbium atom and the radical nature of the DAD ligand in complex 1. The oxidation state of ytterbium in the (C5Me5)2YbDAD—solvent system depends on the coordinating properties of the solvent, whereas the ytterbium atom in the Cp2YbDAD complex (2) remains trivalent regardless of the solvent nature. In complex 2, the redox replacement of DAD·– with 9-fluorenone accompanied by the pinacol dimerization of 9-fluorenone and detachment of one Cp ligand from the ytterbium atom gave rise to the dimeric [CpYb(μ2-OC13H8-C13H8O)(THF)]2 complex (3). The structure of complex 3 was established by X-ray diffraction analysis.
TL;DR: In this paper, the structure of the binuclear thulium(iii) complex with cyclopentadienyl oxide ligand was established by single-crystal X-ray diffraction analysis.
Abstract: Reduction of 2,5-di-tert-butylcyclopentadienone with two equivalents of thulium diiodide in tetrahydrofuran afforded the binuclear thulium(iii) complex with the cyclopentadienyl oxide ligand, viz., TmI2(THF)2[η5-But2C5H2O]TmI2(THF)3 (1). Shielding of the carbonyl carbon atom with two tert-butyl substituents prevents pinacolization of the ketyl radical anions that formed upon one-electron reduction of cyclopentadienone. The reaction of thulium diiodide with an excess of pyridine in tetrahydrofuran gave a product of reductive coupling of two pyridine radical anions, viz., [TmI2(C5H5N)4]2(μ2-N2C10H10) (2). The structures of complexes 1 and 2 were established by single-crystal X-ray diffraction analysis.
TL;DR: The NiCl2·2H2O-Li-arenecat (cat is catalyst) was proposed for use to reduce a wide range of organic compounds, including alkenes, alkynes, carbonyl compounds, imines, halogenated derivatives, sulfonates, aromatic compounds, hydrazines, azo and azoxy compounds, N-oxides, and nitrones as mentioned in this paper.
Abstract: The reducing system NiCl2·2H2O—Li—arenecat (cat is catalyst) was proposed for use to reduce a wide range of organic compounds, including alkenes, alkynes, carbonyl compounds, imines, halogenated derivatives, sulfonates, aromatic compounds, hydrazines, azo and azoxy compounds, N-oxides, and nitrones. The degree of reduction can be controlled for some substrates. Deuterium can be incorporated in the reaction products using nickel chloride deuteriohydrate. Nitrones, N-alkoxyamides, and acyl azides are also reduced with the Li—arenecat system containing no nickel salt.
TL;DR: In this paper, a fragmental descriptor based regression and neural network models for flash point prediction are proposed for flash points of various classes of organic compounds using the fragmental approach in the framework of QSPR methodology.
Abstract: Flash points of various classes of organic compounds were first studied using the fragmental approach in the framework of QSPR methodology. Fragmental descriptor based regression and neural network models for flash point prediction are proposed.
TL;DR: In this paper, the first to fifth generations of carbosilane dendrimers with allyl terminal groups were studied using an adiabatic vacuum calorimeter in the temperature range 6-340 K. The error of measurements was, as a rule, about 0.2%.
Abstract: Temperature dependences of the specific heats, characteristic temperatures, and enthalpies of physical transformations of the first to fifth generations of carbosilane dendrimers with allyl terminal groups were studied using an adiabatic vacuum calorimeter in the temperature range 6—340 K. The error of measurements was, as a rule, about 0.2%. Thermodynamic characteristics of physical transformations of the dendrimers were determined and their thermodynamic functions Cp°(T), H°(T)—H°(0), S°(T)—S°(0), and G°(T)—H°(0) were calculated for the temperature range 0—340 K. The thermodynamic functions of the dendrimers are linearly related to their molecular weights, the number of allyl groups on their outer spheres, and the number of moles of diallylmethylsilane per mole of the dendrimers formed. Additive dependence of the properties of the dendrimers on their chemical composition and structure indicates that the energy of interaction between structural fragments of the dendrimers is independent of the dendrimer generation number. The fractal dimensions, D, of all dendrimers studied in this work are 1.2—1.3 in the temperature range 30—50 K, thus indicating a chain-layered structure of the dendrimer glasses.
TL;DR: An approach based on fragmental descriptors (occurrence number of structural fragments in chemical structures) in conjunction with the artificial neural network technique was developed for predicting physicochemical properties of organic compounds as discussed by the authors.
Abstract: An approach based on fragmental descriptors (occurrence number of structural fragments in chemical structures) in conjunction with the artificial neural network technique was developed for predicting the physicochemical properties of organic compounds. The construction of neural network models for predicting the viscosity, density, and saturated vapor pressure for various classes of organic compounds is discussed.
TL;DR: A method for the synthesis of 1-alkyl-1,2,4-triazolium 4-nitroimides was developed based on alkylation of 4nitramino Na and Ag salts with halo- and dihaloalkanes.
Abstract: A method for the synthesis of 1-alkyl-1,2,4-triazolium 4-nitroimides was developed based on alkylation of 4-nitramino-1,2,4-triazole Na and Ag salts with halo- and dihaloalkanes.
TL;DR: In this paper, the molecular and crystal structure of 6-amino-5-cyano was established by X-ray diffraction analysis, which was used in the synthesis of pyrazole.
Abstract: Substituted 3-hydroxypyrazoles, which were prepared based on ethyl esters of substituted 4-(pyridin-2-ylthio)- or 4-(1,4-dihydropyridin-2-ylthio)acetoacetic acids and hydrazine hydrate, were used in the synthesis of 6-amino-4-aryl-5-cyano-3-(pyridin-2-ylthiomethyl)-2,4-dihydropyrano[2,3-c]pyrazoles. The molecular and crystal structure of 6-amino-5-cyano-3-(3-cyano-4,6-dimethylpyridin-2-ylthiomethyl)-4-(2-nitrophenyl)-2,4-dihydropyrano[2,3-c]pyrazole was established by X-ray diffraction analysis.
TL;DR: Sphingolipids and glycolipids including previously unknown (2S,3S,4R)-1,3,4-trihydroxy-2-(2-(R)-hydroxyoctadecanoylamino)octadec-8E-ene, (2 S,3R)- 1,3-dihydrox-2-octade canoyamino-4E, 8E-hexadecadiene, and (2 H 3 -hexadecyloxypropyl)-α-L-fucopyranos
Abstract: Sphingolipids and glycolipids including previously unknown (2S,3S,4R)-1,3,4-trihydroxy-2-(2-(R)-hydroxyoctadecanoylamino)octadec-8E-ene, (2S,3R)-1,3-dihydroxy-2-octadecanoylamino-4E,8E-hexadecadiene, and (2-hydroxy-3-hexadecyloxypropyl)-α-L-fucopyranoside were isolated from soft corals collected on the shelf near the Andaman Islands (Indian Ocean). The structures of all compounds were established by spectroscopic methods and chemical analyses. The lipids possessed antibacterial activity against Bacillus subtilis, Bacillus pumilus, Escherichia coli, and Pseudomonas aeruginosa and antifungal activity against Aspergillus niger, Rhizopus oryzae, and Candida albicans.
TL;DR: In this paper, the state of the H3PW12O40-I2I2 system was studied using UV, IR, and 31P NMR spectroscopies with variation of the [H2O2] : [HPA] ratio from 2 to 200 during cyclohexene epoxidation.
Abstract: Oxidation of cycloolefins (cyclohexene, cyclooctene, and cyclododecene) with a 30% solution of hydrogen peroxide at 65 °C in the presence of heteropoly acids (HPA) H3PW12–xMoxO40 (x = 0—12), which are precursors of active peroxo complexes, and phase transfer catalysts Q+Cl–, where Q+ is the quaternary ammonium cation containing C4—C18 alkyl groups or [C5H5NC16H33]+, was studied. The catalytic activity decreases in the HPA series: H3PW12O40 > H3PW9Mo3O40 > H3PW6Mo6O40 > H3PW3Mo9O40 > H3PMo12O40. The state of the H3PW12O40—I2I2 system was studied using UV, IR, and 31P NMR spectroscopies with variation of the [H2O2] : [HPA] ratio from 2 to 200 during cyclohexene epoxidation. Despite different catalytic precursors, the reaction proceeds through the same peroxo complex.
TL;DR: In this paper, the influence of salts on the spectrum and intensity of multi-bubble sonoluminescence (SL) of water was observed at a frequency of 20 kHz, and possible mechanisms of the appearance of SL of lanthanides were considered.
Abstract: The influence of salts (TbCl3, Tb(NO3)3, PrCl3, EuCl3, CeCl3, and DyCl3) on the spectrum and intensity of multi-bubble sonoluminescence (SL) of water was observed at a frequency of 20 kHz. Luminescence bands of the lanthanide ions were detected in the SL spectra of concentrated solutions of the CeIII, TbIII, and DyIII chlorides (0.1—1 mol L–1). No luminescence was observed for solutions of the other salts, and the shape of the spectra is due to the absorption of the water SL by the lanthanide ions. Possible mechanisms of the appearance of SL of lanthanides were considered. The first mechanism is the excitation of the lanthanide aqua ions in the solution bulk due to the absorption of the short-wave portion of glow of the excited water molecules and OH radicals emitted from the cavitation gas-vapor bubbles. The second mechanism involves the transfer of the lanthanide ions to the gas phase from the liquid layer adjacent to the cavitation bubble and their excitation in the bubble volume upon collisions with other “hot” or electron-excited particles.
TL;DR: According to low-temperature UV-Vis spectroscopy data, the two-step protonation of iron subgroup metal hydrides with p-nitrophenol includes the formation of ion pairs stabilized by a hydrogen bond between the cationic dihydrogen complex and the phenolate anion as mentioned in this paper.
Abstract: According to low-temperature UV-Vis spectroscopy data, the two-step protonation of iron subgroup metal hydrides [{P(CH2CH2PPh2)3}MH2] (M = Fe, Ru, Os) with p-nitrophenol includes the formation of ion pairs stabilized by a hydrogen bond between the cationic dihydrogen complex and the phenolate anion. The trend of the extent of proton transfer appeared to be aperiodic, FeI ≪ OsI < RuI, in contrast to the previously obtained sequence of the proton-acceptor capacity of the hydride ligand, which increases down the group.
TL;DR: In this article, the formation of polyhedral copper/sodium(potassium) organosiloxanes was examined as a result of hydrolytic condensation of organotrialkoxysilanes in the presence of copper(ii) and sodium or potassium ions.
Abstract: The formation of polyhedral copper/sodium(potassium) organosiloxanes was examined as a result of hydrolytic condensation of organotrialkoxysilanes in the presence of copper(ii) and sodium or potassium ions. High selectivity of the synthesis of copper/sodium(potassium) organosiloxanes having desired structures can be achieved by choosing the reaction conditions.
TL;DR: In this article, the effect of microporous carbon adsorbent contraction was found in the initial temperature interval at relatively low pressures, but the negative value of relative linear deformation ΔL/L smoothly transforms into positive values with the pressure increase.
Abstract: Deformation of the ACC microporous carbon adsorbent during adsorption of carbon dioxide, nitrogen, and argon in the temperature interval from 243 to 393 K and at pressures of 1—5·106 Pa was studied. The effect of adsorbent contraction was found in the initial temperature interval at relatively low pressures. However, the negative value of relative linear deformation ΔL/L smoothly transforms into positive values with the pressure increase. Only the effect of adsorbent expansion is observed at high temperatures in the whole pressure interval. The dependence of the deformation effects for different systems on the adsorbent nature was revealed.