S,O-ligand-promoted palladium-catalyzed C–H olefination of arenes with allylic substrates

An efficient catalytic system for the C–H olefination of arenes with different allylic substrates is reported. The catalytic system is based on Pd(OAc)₂ and a readily accessible bidentate S,O-ligand. The methodology shows high activity with a wide range of arenes, including bulky and, electron-rich and -poor arenes. The applicability of this catalyst is demonstrated in the late-stage functionalization of the complex molecule O-methylestrone.     

Reactivity of the Ge–H,Sn–H,P–H,and Se–H Bonds in Radical Abstraction Reactions

The experimental data for the liquid- and gas-phase reactions of atoms and radicals with organoelement compounds R _{n – 1}E–H

PECVD synthesis of As–S glasses

Chalcogenide glasses of the As–S system were first obtained by melting of solid products of interaction between As and S in low-temperature argon plasma. The plasma-chemical synthesis was performed at a reactor wall temperature not exceeding 250°C. The content of S in the As–S glasses is 54 to 72 mol %. The elemental, phase, and impurity composition of the glasses and their glass-transition point and optical properties were studied.     

Solubility of Native Gold in H—O—S Fluids at 100–400°C and High H2S Content

Reaction of MgS, water, and air in sealed gold capsules at 100 to 400°C and0.15 GPa is used to generate an aqueous fluid with very high (20.6 m) H₂Scontent and to remobilize significant quantities of native gold as gold sulfides.A combination of X-ray photoelectron and Auger electron spectroscopy (XPS,AES), analytical scanning-electron microscopy (SEM—EDX),electron-micro-probe analysis (EPMA), and calculated solution properties shows that the goldsulfides precipitated during quenching and later perforation of the capsulesrepresent native gold dissolved as Au(I)-bisulfide under the experimental conditions.The equilibrium constant (logK) for the reaction:Au(s) H₂S(aq) + HS^– = Au(HS)₂ ^– + 1/2H₂(g)ranges from –3.96 ± 0.40 at 115°C to –1.06 ± 0.32 at 400°C; it is in goodagreement with literature values for 25°C and 300–350°C, and varies inverselywith absolute temperature T[–H ⁰ ₁/(2.303R)= –2644 ± 33K; r = 1.00]. Themaximum solubility of native gold in this study (29.4 g/kg at 200°C) issignificantly greater than that from published studies on Au(I)-bisulfides and maystimulate interest in developing bisulfides as gold-complexing agents in goldextraction technology.     

Kinetics of H2S destruction in the radiolysis of CH4−H2S gas mixtures

The kinetics of H₂S destruction in the radiolysis of CH₄–H₂S and CH₄–H₂S–O₂ mixtures has been studied. It has been shown that G(–H₂S) depends on amounts of hydrogen sulfide and the presence of oxygen in the starting mixture and is within the range of 5–13 mol/100 eV. G(H₂) decreases with the increases of O₂ content and amounts to the constant value of 2.     

Melt–Vapor Phase Diagram of the Te–S System

The values of partial pressure of saturated vapor of the constituents of the Те–S system are determined from boiling points. The boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor–liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation–condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium.     

Hydrocarbons as proton donors in C–H⋯N and C–H⋯S hydrogen bonds

C–H?N and C–H?S hydrogen bonds were analyzed in complexes where acetylene, ethylene, methane and their derivatives are proton donors while ammonia and hydrogen sulfide are proton acceptors. Ab initio calculations were performed to analyze those interactions; MP2 method was applied and the following basis sets were used: 6-311++G(d,p), aug-cc-pVDZ and aug-cc-pVTZ. The results showed that hydrogen bonds for complexes with ammonia are systematically stronger than such interactions in complexes with hydrogen sulfide. If the fluorine substituted hydrocarbons are considered then F-substituents enhance the strength of hydrogen bonding. For a few complexes, mainly those where carbon atom in proton donating C–H bond possesses sp³ hybridization, the blue-shifting hydrogen bonds were detected. Additionally, Quantum Theory of ‘Atoms in Molecules’ and Natural Bond Orbitals method were applied to analyze H-bond interactions.     

Copper and zinc co-catalyzed synthesis of imidazoles via the activation of sp C–H and N–H bonds

An efficient and facile approach to synthesize imidazoles from amidines and arylketone via oxidative coupling of sp³ C–H bond and N–H bond is reported. This strategy exhibits high performance in terms of regioselectivity with moderate to high yields by using easily available materials, and provides an alternative method to synthesize multi-substituted imidazole skeletons.     

Compounds of Undecahydrodecaborate Anion B10H11–

Conditions for the synthesis of salts of the B₁₀H₁₁ ^–anion with different cations in the Cat₂B₁₀H₁₀+ RCOOH (R = H, CF₃; Cat = Me₄N⁺, Et₄N⁺, Bu₄N⁺, Ph₄P⁺, Ph₄As⁺) systems were studied depending on the acid strength (pK _a) and size of the cation. It was established that reactions with trifluoroacetic acid give compounds of this anion with any one of the quaternary ammonium, phosphonium, or arsonium cations, while formic acid can only give salts with the largest of these cations.     

Thermoanalytical study and structure of stoichiometric As–Sb–S glasses

The glass-forming system (As₂S₃)_100?x(Sb₂S₃)_x was studied by thermal analysis (conventional and StepScan differential scanning calorimetry) and Raman spectroscopy. It was found that the bulk glasses are homogeneous up to x = 60, while supercooled melts are unstable and when x ≥ 40, Sb₂S₃ (stibnite) crystallizes during heating. Depending on the chemical composition, the glass transition temperature initially increases as the Sb₂S₃ concentration is increased from 0 to 5 %, decreases to a minimum at ~20 %, and then gradually increases as the concentration is further increased and the main Raman peak also shifts non-monotonically. Combining these results with chemometric analysis of the Raman spectra showed that the image of the structure of the studied glasses can be described by the linear combination of three chemically different stable clusters, rather than by the chains crossing model, CCM, and that the properties of the glasses are controlled by medium-range order.     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

The phase diagram of the Ga–S system in the concentration range of 48.0–60.7 mol% S

Journal of Thermal Analysis and Calorimetry - A novel flame-retarded epoxy resins system is prepared by copolymerizing diglycidyl ether of bisphenol A (EP) with tris(3-nitrophenyl) phosphine...     

Synthesis of complex Si–O–N–H derivatives by molecular bombardment of silicon and silicon dioxide

Bombardment of a silicon target in a high vacuum with a molecular beam (mixture of high energy H₂+N₂, obtained by charge exchange) and a thermal beam of O₂ produces on the target a variety of compounds. The target is then bombarded by the same molecular beams which produce, extracted by an electrostatic field at an energy of about 10 keV, molecular ions due to the compounds thus formed. These ions are analysed (electromagnet) to give a primary spectrum of ions according to their mass, which are individually selected and dissociated in a collision cell (same H₂+N₂ mixture). Mass analysis of the dissociation fragments leads to the identification of silicon clusters (Si)_n and of Si–O–N–H derivatives, the fragmentations of which permit a definitive determination of their molecular complexity. Dissociation spectra have thus been obtained for some of the most intense peaks of the primary spectrum, on the one hand, and on the other hand for some peaks of lower intensity but of special interest to us (see below). The composition of the fragments is confirmed by the study of the satellite ions derived from the natural 28, 29 and 30 isotopes of silicon, and by the use of deuterium instead of hydrogen. None of the Si–O–N–H derivatives obtained was apparently known earlier. It is shown that some of these molecules (those ‘of special interest to us’) may be identical with sila-analogues of standard amino acids and of nucleic bases: the fact that their fragmentations are identical with those of the corresponding carbon analogues speaks in favour of a structural identity. However, one cannot yet distinguish between the various possible isomeric arrangements, as none of them has been independently prepared, which excludes a direct comparison with reference samples, and as these isomers might give identical fragments; we hope to be able to resolve this ambiguity later. Anyhow, the substances formed are the most complex molecular silicon derivatives so far produced: e.g. Si₂O₂NH₅, Si₃O₂NH₇, Si₄O₃NH₉, Si₄O₂N₂H₄, Si₄ON₃H₅, Si₅O₃N₂H₁₀, Si₅O₂NH₁₁, corresponding to sila-glycine, sila-alanine, sila-threonine, sila-uracile, sila-cytosine, sila-valine, sila-glutamine, – or isomers. Similar results have been obtained using a silicon dioxide target and high energy molecular beams of hydrogen and of nitrogen, without thermal oxygen, or with a carborundum target. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASmolecular impact / silicon derivatives / amino-acid silicon analogues     

Preparation and electrocatalytic performance of Fe–N–C for electroreduction of H2O2

Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen source, and calcination temperature on the catalytic performance of the Fe–N–C for H₂O₂ electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed good performance and stability for electroreduction of H₂O₂ in alkaline solution. An Al–H₂O₂ semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V and its power density reached 51.4 mW cm⁻² at 65 mA cm⁻².     

Phase Diagrams of Fullerenol-d–LaCl3–H2O and Fullerenol-d–GdCl3–H2O Systems at 25°С

Russian Journal of Physical Chemistry A - Isothermal phase diagrams of ternary systems fullerenol-d–LaCl3–H2O and fullerenol-d–GdCl3–H2O at 25°C are studied via...     

Research into the simultaneous removal process of H2S and PH3 by Cu–Fe–Ce composite metal oxide adsorbent

In this study, a Cu–Fe–Ce composite metal oxide adsorbent was synthesized by chemical precipitation method to simultaneously remove H₂S and PH₃. The effects of reaction temperature, oxygen content, gas inlet concentration and gas hourly space velocity (GSHV) were studied. The DRIFTS results showed that excessive oxygen and high reaction temperature lead to excessive conversion of H₂S, which competed with adsorption–oxidation of PH₃, and it was not conducive to simultaneous removal of H₂S and PH₃, and it was found that high concentration of H₂S was more likely to cause deactivation of the adsorbent than PH₃. GHSV affected the contact time between the adsorbent and the gas and affected the removal effect. The BET results showed that a larger specific surface area was more conducive to gas adsorption, and thus had a better removal effect. The XPS results showed that the deactivation of the adsorbent was due to the formation of sulfur-containing and phosphorus-containing substances.

     

Kinetic analysis of the crystallization processes in the glasses of the Bi–As–S system

Kinetic analysis of the crystallization process in Bi₄(As₂S₃)₉₆ and Bi₆(As₂S₃)₉₄ glasses was performed based on DSC curves recorded under non-isothermal measurement conditions. Samples were thermally treated at different heating rates in the temperature range 300?C770?K. The activation energy of crystallization E and the pre-exponential factor K ₀ are determined by the Kissinger method and the characteristic crystallization parameters m and n of investigated glasses by the Matusita method. For both crystallization processes the glass with 4 at.% of Bi is characterized by the mechanism of volume nucleation, which is manifested in the form of two-dimensional growth at the first crystallization process, and as three-dimensional at the second one. On the other hand, in the sample with 6 at.% Bi, the average value of the parameter m is close to one, which indicates one-dimensional crystal growth. Compatibility of the values of the parameters m and n suggests that this sample has a large number of crystallization centers, which do not increase significantly during the thermal treatment.     

Dissociation energies of O–H bonds in 3-pyridinols

The O?H bond dissociation energy (D _O?H) has been estimated for 20 substituted 3-pyridinols and a substituted 3-pyrimidinol from experimental kinetic data by the intersecting parabolas method using α-tocopherol and 4-methoxyphenol as reference compounds. The following D _O?H values (kJ/mol) have been obtained: 363.7 for 3-pyridinol, 365.3 for 2-alkyl-3-pyridinols (five compounds), 358.8 for 2-alkyl-6-methyl-3-pyridinols (six compounds), 378.1 for 5-benzyl-3-pyridinol, 353.2 for 2,4,6-trimethyl-3-pyridinol, 340.9 for 2-benzyl-6-methoxy-3-pyridinol, 345.8 for 2,6-dimethoxy-5-benzyl-3-pyridinol, 381.7 for 2-ethyl-4-nitro-6-methyl-3-pyridinol, 376.8 for 2-isopropyl-4-nitro-6-methyl-3-pyridinol, 318.3 for 2,4-dimethyl-6-dimethylamino-3-pyridinol, 357.3 for mexidol, and 322.2 for 2,4-dimethyl-6-dimethylamino-3-pyrimidinol. The substituent effect on the O?H bond dissociation energy in 3-pyridinols is considered. The stabilization energies of pyridinoxyl and phenoxyl radicals are compared. The activation energies and rate constants have been calculated for a series of reactions of various radicals with 3-pyridinols.