Showing papers in "Russian Chemical Bulletin in 1996"
TL;DR: In this article, the results on hyd rode halogenation (HDH) of alkyl halides, freons, aryl halide, polychlorinated derivatives of benzodioxines and biphenyls, and other compounds in the presence of heterogeneous and homogeneous catalysts are generalized, effective and selective hydrodehalogenation proceeds via anion or radical anion intermediates.
Abstract: Recent results on hyd rode halogenation (HDH) of alkyl halides, freons, aryl halides, polychlorinated derivatives of benzodioxines and biphenyls, and other compounds in the presence of heterogeneous and homogeneous catalysts are generalized, Effective and selective hydrodehalogenation proceedsvia anion or radical anion intermediates Special attention is given to the nature of the source of the hydrogen replacing the halogen
55 citations
TL;DR: In this article, the authors analyzed many variants of nucleophilic aromatic substitution of hydrogen proceeding according to an addition-elimination pattern reveals that this is the major reaction pathway, whereas nucleophilia replacement of halogen or another nucleofugal group is the secondary process, i.e., prefix substitution.
Abstract: Analysis of many variants of nucleophilic aromatic substitution of hydrogen proceeding according to an addition—elimination pattern reveals that this is the major reaction pathway, whereas nucleophilic replacement of halogen or another nucleofugal group is the secondary process, i.e.,ipso-substitution. In this respect electrophilic and nucleophilic aromatic substitution can be considered as analogous processes.
53 citations
TL;DR: Lower alkanes (ethane, propane, n-butane,n-pentane) are readily oxidized in acetonitrile solvent by H2O2 with vanadate anion to produce predominantly or exclusively ketones (aldehydes).
Abstract: Lower alkanes (ethane, propane,n-butane,n-pentane) are readily oxidized in acetonitrile solvent by H2O2 with vanadate anion — pyrazine-2-carboxylic acid (PCA), as the catalyst at 75 °C and pressures of −3 atm to produce predominantly or exclusively ketones (aldehydes). Isobutane is transformed selectively intotert-butyl alcohol. The oxidation of cyclohexane at 26 °C in acetone or acetic acid is less efficient than in acetonitrile. The reaction does not occur intert-butyl alcohol.
36 citations
28 citations
TL;DR: In this paper, the first tetramethyl(2-methylthioethyl)cyclopentadiene (1) was synthesized for the first time, and the S→Zr coordination bond was shown to exist in complex3 both in the crystalline state and in solution.
Abstract: Chelating sulfur-containing cyclopentadienyl ligand tetramethyl(2-methylthioethyl)cyclopentadiene (1), was synthesized for the first time. Its sodium (2a) and lithium (2b) derivatives were isolated in the crystalline state. Starting from compound1 some novel ZrIV complexes were prepared: [tetramethyl(2-methylthioethyl)cyclopentadienylltriclllorozirconium (3), bis[tetramethyl(2-methylthioethyl)cyclopentadienylldichlorozirconium (4), and [pentamethylcyclopentadienyll [tetramethyl(2-methylthioethyl)cyclopentadienylldichlorozirconium (5). The crystal structures of3 and5 were determined by X-ray diffraction analysis. The dynamic behavior of complex3 in various solvents was investigated by1H and13C N MR spectroscopy. The S→Zr coordination bond was shown to exist in complex3 both in the crystalline state and in solution. No coordination of this type was found in compounds4 and5.
24 citations
TL;DR: In this article, four methods for calculating the enthalpies of sublimation of organic molecular crystals based on different methodological approaches are proposed, and their good predictive ability with respect to various classes of compounds (aliphatic nitro compounds, acyclic and cyclic amines, amides and amino acids, benzene derivatives, heterocyclic compounds, etc.) was demonstrated.
Abstract: Four methods for calculating the enthalpies of sublimation of organic molecular crystals based on different methodological approaches are proposed. Comparative analysis of these methods was carried out and their good predictive ability with respect to various classes of compounds (aliphatic nitro compounds, acyclic and cyclic amines, amides and amino acids, benzene derivatives, heterocyclic compounds,etc.) was demonstrated.
23 citations
TL;DR: The formation of free radicals in the process of direct fluorination of natural and synthetic polymers at temperatures close to 77 K was studied by ESR as discussed by the authors, and the maximum concentrations of radicals, (1017 −5·1018 spin g−1) and their complete oxidation were observed in the temperature interval from 77 to 250 K at a fluorine pressure of 30 Torr.
Abstract: The formation of free radicals in the process of direct fluorination of natural and synthetic polymers at temperatures close to 77 K was studied by ESR. The maximum concentrations of radicals, (1017–5·1018 spin g−1) and their complete oxidation were observed in the temperature interval from 77 to 250 K at a fluorine pressure of 30 Torr. The initiation of chain halogenation, which consists of homolytic breaking of chemical bonds to yield free-radical intermediates. was examined in the framework of the multi-center synchronous transitions model.
20 citations
TL;DR: N,N-Dinitro derivatives of alkylurethanes, benzamide, and p-toluenesulfamide were synthesized for the first time.
Abstract: N,N-Dinitro derivatives of alkylurethanes, benzamide, andp-toluenesulfamide were synthesized for the first time. Their reactions with ammonia afforded the ammonium salt of dinitramide in 44–85% yields.
19 citations
TL;DR: In this article, a comparison of various methods of empirical scaling of quantum-mechanical harmonic molecular force fields has been performed, and the efficiency of using each particular scaling technique was shown to depend on the theoretical level of the quantum measurement.
Abstract: Comparative analysis of various methods of empirical scaling of quantum-mechanical harmonic molecular force fields has been performed. The efficiency of using each particular scaling technique was shown to depend on the theoretical level of the quantum-mechanical calculation. The Pulay method of scaling (congruent transformation of the force constant matrix) is applicable in the case where the relative accuracies of determination of diagonal and off-diagonal quantum-mechanical force constants are approximately equal. This requirement is satisfied for a quantum-mechanical force field determined close to the HartreeFock limit. This makes it possible to carry out its correction with maximum retention of the peculiarities inherent in the molecule under investigation.
18 citations
TL;DR: The results of ESR spectroscopic studies of radical reactions of fullerenes are presented in this article, where the properties of the spin adducts resulting from polyaddition of free radicals to fulenes and of fulenyl radicals containing η2-bonded metaIloco mplexes are discussed.
Abstract: The results of ESR spectroscopic studies of radical reactions of fullerenes are presented. Reactivities of radicals of various chemical natures with respect to C60 and C70, delocalization of the unpaired electron in monofullerenyl radicals, and their reactivity are considered. The examples of dynamic effects in the ESR spectra of fullerenyl radicals, associated with the hindered rotation of the attached radicals, are presented. Characteristic features of the structures of the spin adducts resulting from polyaddition of free radicals to fullerenes and of fullerenyl radicals containing η2-bonded metaIloco mplexes are discussed.
18 citations
TL;DR: In this paper, the reactivity of bis(siloxy)silanone groups (≡Si-0)2Si=O stabilized on a silica surface with respect to H2 molecules was studied.
Abstract: The reactivity of bis(siloxy)silanone groups (≡Si-0)2Si=O stabilized on a silica surface with respect to H2 molecules was studied. The reaction was found to give the (≡Si-O)2SiH(OH) groups. The rate constant for this process was determined. Its activation energy in the 300–580 K temperature range is 13.4±0.3 kcal mol−1, and the enthalpy is 54±5 kcal mol−1. The activation energy for the reverse reaction,viz., elimination of a hydrogen molecule, is equal to ∼65 kcal mol−1. Quantum-chemical calculations of hydrogenation of F2Si=O and (HO)2Si=O, which are the simplest molecular models of the silanone groups, were performed. Data on the geometrical and electronic structures of transition states and on the effects of substituents at the silicon atom on the reactivity of the silanone groups in this process were obtained. The optical absorption band of the surface silanone groups was quantitatively characterized. Its maximum is located at 5.65±0.1 eV; the extinction coefficient at the maximum e(220 nm) is (3±0.5) · 10−18 cm2 molec.−1.
TL;DR: Tetrabutylammonium hydroxyundecahydro-closo-dodecaborate was obtained in high yield via [B12H11NMP]−(NMP =N-methylpyrrolidone) by the modified method [Bi2H11OH]2− is easily acylated by aromatic acyl chlorides to give novel compounds as mentioned in this paper.
Abstract: Tetrabutylammonium hydroxyundecahydro-closo-dodecaborate was obtained in high yield via [B12H11NMP]−(NMP =N-methylpyrrolidone) by the modified method [Bi2H11OH]2− is easily acylated by aromatic acyl chlorides to give novel compounds [B12H11OCOAr]2− in high yields All the compounds were characterized by standard and special NMR methods
TL;DR: In this paper, the selectivity of the reaction depends on the presence of the solvent, its polarity, and, to a lesser degree, on the temperature of the solution.
Abstract: Phosphorylation of dihydric phenols with triamides of phosphorous acid was performed under different reaction conditions and using reactants taken in various ratios. The selectivity of the reaction depends on the presence of the solvent, its polarity, and, to a lesser degree, on the temperature.
TL;DR: The isomerism of binuclear complexes is due to the different ways of coupling of the alkyne fragments of the diyne, namely, "head-to-head", "headto-tail" or "tail-totail".
Abstract: Diyne FcCmCC.CFc (Fc is ferrocenyl) reacts with Ru3(CO)12 in boiling hexane to yield binuclear complexes Ru2 and Ru2(CO)6(C4Fc2(C=CFc)2C=O) containing ruthenacyclopentadiene and diruthenacycloheptadienone rings, respectively. The isomerism of the complexes is due to the different ways of coupling of the alkyne fragments of the diyne, namely, “head-to-head”, “head-to-tail” or “tail-to-tail”. The reaction of enyne PhC=CCH=CHPh with Ru3(CO)12 under similar conditions gives isomeric binuclear complexes Ru2(CO)6(C4Ph2(CH=CHPh)2) and trinuclear clusters Ru3(CO)6(w-CO)2(C4Ph2(CH=CHPh)2) and Ru3(CO)8(μ3-,η1-η1-η4-η2 C4Ph2(CH=CHPh)2). The structure of the latter was determined by X-ray diffraction analysis. The Ru3 triangle coordinates eight terminal CO groups and the organic ligand resulting from the “head-to-head” dimerization of enyne molecules; the ruthenacyclopentadiene moiety is η4-coordinated to the Ru(CO)2 group, and the third ruthenium atom is η2-bound to one of the PhCH=CH groups.
TL;DR: N-(2-hydroxy-3-methyl-2-phenylcyclohexyl)-N-diphenylmethylnitroxyl was characterized by X-ray diffraction analysis for the first time as discussed by the authors.
Abstract: Nitroxyl radicals containing the diphenylmethyl group as one of the substituents at the nitroxyl group are stable compounds that can be isolated in an individual state.N-(2-Hydroxy-3-methyl-2-phenylcyclohexyl)-N-diphenylmethylnitroxyl was characterized by X-ray diffraction analysis for the first time.
TL;DR: In this paper, the kinetic parameters of the thermal decomposition of several pairs of 1(2)-R-5-R′-disubstituted tetrazoles have been determined using the manometric method.
Abstract: The kinetic parameters of the thermal decomposition of several pairs of 1(2)-R-5-R′-disubstituted tetrazoles have been determined using the manometric method. The isomers differ only by the position of the substituents linked with the heterocyclic nitrogen atom. The activation entropies are equal to ca. +8 cal mol−1 K−1, the activation energies range from 39 to 48 kcal mol−1. A linear correlation between the logarithms of the rate constants of decomposition of the isomers has been established. The limiting stages of the stepwise mechanism of the monomolecular decomposition, which determines the experimental rates of nitrogen evolution, include the reversible formation followed by decomposition of intermediate azidoazomethines in the case of 1,5-disubstituted tetrazoles and azodiazo compounds for isomeric 2,5-disubstituted tetrazoles. The enthalpies of formation of R(N3)C=NR (R = Me, Ph), C2H3(N3)C=NMe and increments ΔfH°[Cd−(C)(N3)], ΔfH°[Cd-(Cb)(N3)], and ΔfH°[Cd−(Cd)(N3)] have been estimated.
TL;DR: Attention is focused on the mechanisms of action of horseradish peroxidase in reactions with different substrates and on correlations between structure and functions of various heme-containing proteins.
Abstract: The structure and functions of peroxidases are characterized. Attention is focused on the mechanisms of action of horseradish peroxidase in reactions with different substrates and on correlations between structure and functions of various heme-containing proteins. The phenomenon of substrate-substrate activation typical of peroxidase-catalyzed reactions is discussed.
TL;DR: The structural-kinetic concept of chemicalligation was created and the relationship between the reactivity of interacting groups and sequence-dependent local conformation of the ligation site in B-DNA was established and the lesser efficiency of chemical ligation of RNA fragments in comparison to that of DNA analogs was demonstrated and rationalized.
Abstract: A new procedure was developed as an alternative to the enzymatic assembly of natural and modified double-stranded DNAs using chemical reagent (chemical ligation). BrCN was suggested as an efficient coupling reagent, which induces superfast reactions in DNA duplexes. The physicochemical properties and the structure of new types of DNA duplexes, which are the substrates for chemical ligation, with breaks in phosphodiester chains, including concatemers, were studied. Chemical ligation was applied to prepare biologically active 17–200 base-pair double-stranded DNAs and DNA-RNA block-copolymers, to incorporate various modifications into DNA duplexes including pyrophosphate and phosphoramidate unnatural internucleotide bonds. The unique possibilities of this approach were demonstrated in the development of methods for circularization of oligodeoxy ribonucleotides and assembly of branched DNAs. The structural-kinetic concept of chemicalligation was created and the relationship between the reactivity of interacting groups and sequence-dependent local conformation of the ligation site in B-DNA was established. The lesser efficiency of chemical ligation of RNA fragments in comparison to that of DNA analogs was demonstrated and rationalized. This approach was used as a sensitive monitor of a stable double helix formation and third-strand binding to a DNA duplex.
TL;DR: In this article, the major factors determining molecular weights of polyarylene-ether ketones formed by the reaction of 4,4′-difluorobenzophenone with 2,2-bis(4-hydroxyphenyl)propane in the presence of K2CO3 were revealed.
Abstract: The major factors determining molecular weights of polyarylene-ether ketones formed by the reaction of 4,4′-difluorobenzophenone with 2,2-bis(4-hydroxyphenyl)propane in the presence of K2CO3 were revealed. The optimum conditions for the preparation of high-molecular-weight polymers were found, and it was demonstrated that it is possible to control their molecular weights (\(\bar M_W \) from 10 000 to 200 000).
TL;DR: A new neutral π-arene complex of trivalent uranium, (η6-C6H5Me)U(AlCl4)3 (1), was obtained by the reductive Freidel-Crafts reaction.
Abstract: A new neutral π-arene complex of trivalent uranium, (η6-C6H5Me)U(AlCl4)3 (1), was obtained by the reductive Freidel-Crafts reaction. The crystal structure of 1 was determined by single crystal X-ray diffraction analysis. The U atom in 1 is bound to the C6H5Me group by the η6 mechanism and is linked to the three AICl4 groups through two g-CI bridges. The coordination of the U atom is a distorted pentagonal bipyramid in which the center of the arene ring is in one apical position, and the bridging Cl atoms occupy the other vertices.
TL;DR: Several novel zirconium(iv) complexes with the chelating oxygen-containing cyclopentadienyl ligand, tetramethyl(2-methoxyethyl)cyclopentadiene, have been synthesized as mentioned in this paper.
Abstract: Several novel zirconium(iv) complexes with the chelating oxygen-containing cyclopentadienyl ligand, tetramethyl(2-methoxyethyl)cyclopentadiene, have been synthesized. [η5:η1-Tetra-methyl(2-methyl)cyclopentadienyl]trichlorozirconium (2), bis[η5-tetramethyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (3), [η5-pentamethylcyclopentadienyl][η5-tetra-methyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (4), and [η5-tetra-methyl(2-methylthioethyl)cyclopentadienyl][η5-tetramethyl(2-methoxyethyl)-cyclopentadienyl]dichlorozirconium (5) have been prepared from the corresponding lithium cyclopentadienide (l). The crystal structure of cyclopentadienyl complex2 has been established by X-ray analysis. The coordination O→Zr bond in compound2 exists both in the crystalline state and in solutions. No coordination of this type was observed in complexes3–5. Synthesized complexes2–5 are discussed in comparison with their sulfur-containing analogs.
TL;DR: A novel optically active exo-metallofullerene derivative, η2-C60Pt[(+)-DIOP] (1) (DIOP is 2,3o,o'-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphinobutane)), is formed as a result of the cleavage of the chelate metallocycle in Pt[(+)DIOP]-2 and the substitution of the bidentate (+)-diOP
Abstract: A novel optically active exo-metallofullerene derivative, η2-C60Pt[(+)-DIOP] (1) (DIOP is 2,3-o,o'-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphinobutane)), is formed as a result of the cleavage of the chelate metallocycle in Pt[(+)-DIOP]2 and the substitution of the bidentate (+)-DIOP ligand with C60. Cluster 1 was also obtained by replacement of the phosphine ligands in η2-C60Pt(PPh3)2 by (+)-DIOP. Compound 1 was identified by its electronic absorption spectra,31P NMR spectra, and the elemental analysis data. A singlecrystal X-ray study of the 1 cyclooctene solvate, η2-C60Pt[(+)-DIOP] C8H14 was performed. Packing of the fullerene cores in a crystal of 1 · C8H 14 corresponds to the diamond structure subjected to the significant orthorhombic distortions.
TL;DR: In this paper, the 1H,23Na, and 7Li NMR spectra of 2-hexylsodiurn, 2-ethylhexyllithium, and 2 -ethylhexyl chloride with NaCl have been recorded.
Abstract: 1H,23Na, and7Li NMR spectra of 2-ethyl hexylsodiurn, 2-ethylhexyllithium, and isobutyllithium obtained in the reaction of the corresponding alkyl chlorides and metals have been recorded. The1H N MR signal for the protons of the CH2Na group is shifted upheld compared with that for the protons of the CH2Li group (doublets at δ -0.88 and δ -0.83, respectively). The composition of the products of reaction of 2-ethylhexyl chloride with sodium depends on the form of the metal reagent employed. The use of sodium balls with diameter up to 2 mm results in the formation of products containing ionic chlorine (30–50 % with respect to Na); the reaction with the dispersion proceeds faster and the reaction product is chlorine-free. The23Na NMR spectra of these substances are also different, which is explained by the formation of 2-ethylhexylsodium complexes with NaCl in the former case.
TL;DR: Isocryptolepine, an alkaloid recently isolated from the roots ofCryptolepis sanguinotenta, was synthesized by selective methylation at the N(5) atom of 11H-indolo(3,2-c]quinoline with excess Mel in toluene.
Abstract: Isocryptolepine, an alkaloid recently isolated from the roots ofCryptolepis sanguinotenta, was synthesized by selective methylation at the N(5) atom of 11H-indolo(3,2-c]quinoline with excess Mel in toluene.
TL;DR: Fullerene deuteride was obtained by the reaction of deuterium with solid palladium fulleride C60Pd4.9 under fairly mild conditions as mentioned in this paper.
Abstract: Fullerene deuteride was obtained by the reaction of deuterium with solid palladium fulleride C60Pd4.9 under fairly mild conditions. The compound was identified by FD-MS, UV-Vis and IR spectroscopies, and TLC.
TL;DR: In this article, the authors studied the thermal decomposition of ammonium persulfate by calorimetry and Raman spectroscopy and estimated the activation energies of the overall reaction and its individual stages.
Abstract: Kinetics of thermal decomposition of ammonium persulfate was studied by calorimetry and Raman spectroscopy. The values of activation energies of the overall reaction and its individual stages were estimated.
TL;DR: In this paper, the magnetic moments of these complexes correspond to the oxidation state + 3 of the metal atoms and were obtained by reactions of LnI3(THF)3 (Ln = Ce, Pr, Nd or Gd) with lithium and excess naphthalene.
Abstract: The [LnI2(THF)3]2(μ-C10H8) complexes were obtained by reactions of LnI3(THF)3 (Ln = Ce, Pr, Nd, or Gd) with lithium and excess naphthalene. The magnetic moments of these complexes correspond to the oxidation state +3 of the metal atoms. The YbII complex, [YbI(DME)2]2(μ-C10H8), was synthesized by the reaction of YbI2(DME)2 with an equimolar amount of naphthalenelithium.
TL;DR: The manganese(III) acetate-mediated electrooxidative ring opening of 1-methylcyclobutanol (1) in acetic acid affords pentane-2-one (2) as the major product.
Abstract: The manganese(III) acetate-mediated electrooxidative ring opening of 1-methylcyclobutanol (1) in acetic acid affords pentane-2-one (2) as the major product. The reaction of 1-methylcyclobutanol with Mn(OAc)3-LiCl gives 5-chloropentane-2-one (4.
TL;DR: The lifetime of the room-temperature phosphorescence (RTP) of s-cyclodextrinphenanthrene-chloroform complexes in water at 274 K increases from 1.7 to 2.3 s as the concentration of chloroform increases.
Abstract: The lifetime of the room-temperature phosphorescence (RTP) of s-cyclodextrinphenanthrene-chloroform complexes in water at 274 K increases from 1.7 to 2.3 s as the concentration of chloroform increases from 2.5 · 10−3 to 0.125 mol L−1. This dependence is explained by the formation of insoluble aggregates possessing RTP.
TL;DR: In this article, the adsorption of polynuclear palladium(ii) hydroxocomplexes (PHC) by carbon materials (CM) was studied and it was found that PHC are adsorbed from aqueous solutions without a change in their chemical composition and are composed of clusters with metalmetal distances typical of the PdO chain structure.
Abstract: Adsorption of polynuclear palladium(ii) hydroxocomplexes (PHC) by carbon materials (CM) was studied. It was found that PHC are adsorbed from aqueous solutions without a change in their chemical composition and are composed of clusters (<10 A) with metalmetal distances typical of the PdO chain structure. Three-dimensional ordered particles with the PdO structure were formed upon adsorption of PlIC on carbon materials at room temperature or after the PHC suspension was dried in air at 400 °C (the size of the particles was 15 and 25 A, respectively). Calculation of the electron-microscopic images of the adsorbed PHC with atomic resolution based on crystal structure modeling showed that PdO particles containing -100 palladium atoms is the final product after drying of the adsorbed PHC.