Electrochemical reduction of oxygen to hydrogen peroxide in a gas-diffusion electrode based on mesoporous carbon

Mesoporous carbon prepared by template synthesis using SBA-15 mesostructured silicate material was tested as an electrocatalyst for electrochemical synthesis of Н₂О₂ from О₂ in a two-layer gas-diffusion electrode. Preparative syntheses of Н₂О₂ in 0.06 to 2.0 M aqueous solutions of various electrolytes (pH 2–8) were performed at current densities in the interval 0.05–0.19 A cm^–2. Solutions with an Н₂О₂ concentration of 1–2.8 M were prepared with 46–70% current efficiency. Thus, the material tested shows promise as an electrocatalyst of two-electron reduction of oxygen to Н₂О₂.     

Thermodynamic Analysis of the Behavior of Trimethyl Borate as a Precursor for Chemical Vapor Deposition of Boron-Containing Films

The chemical vapor deposition (CVD) of boron-containing films involving the trimethyl borate precursor has been modeled in the ranges of pressures 0.03 ≤ Р, Torr ≤ 760 and temperatures 300 ≤ Т, K ≤ 2000. The CVD diagram of this system was found to feature existence fields of the following phase complexes: В + В₄С, В4С + В₂О₃, С + В₂О₃ + В₄С, С + В₂О₃, С + В₂О₃ + НВО₂, С + НВО₂, С + В₄С, and a В₄С phase.     

Selective monoallylation of β-cyclodextrin

Reaction of β-cyclodextrin with allyl bromide in dimethyl sulfoxide affords 2-О-allyl-β-cyclodextrin, while in dimethylformamide 6-О-allyl-β-cyclodextrin is formed. Optimal conditions of the reaction were found allowing to obtain the target products in quantitative yield.     

Interpretation and Simulation of Negative Ion Mass Spectra of Some Phosphorus Organoelement Compounds

Negative ion mass spectra for a series of organophosphorus compounds were obtained and negative ion fragmentation processes were treated theoretically. Using O-isopropyl and O-pinacolyl methylphosphonofluoridates as examples, electron affinities of molecules and their fragments were estimated using the UB3LYP/6-311+G(d,p) quantum-chemical approach and energetically more favorable and characteristic routes of dissociative electron attachment, including simple bond cleavage and rearrangements, were determined. Based on the obtained experimental and theoretical data, hypothetic fragmentation patterns were proposed and a special algorithm was compiled to predict negative ion mass spectra for some groups of organophosphorus compounds, such as О-alkyl methylphosphonofluoridates, О,О-alkyl phosphonodichloridates, and О,О′-dialkyl phosphonochloridates. The simulated mass spectra showed a good agreement with the experimental ones, confirming reasonable reliability of the proposed algorithm.     

The Quantum Yield of Singlet Oxygen in Thermal Degradation of Alcohol Hydrotrioxides

The yield of singlet oxygen (¹О₂) in the decomposition of a number of hydrotrioxides of alcohols (cyclobutanol, cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, L-menthol, 1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol, 1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol, heptan-4-ol, propanol-2, and 1-cyclopropylethanol) has been determined using the IR chemiluminescence technique. It has been shown that cyclopentanol, 1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol and 1-cyclopropylethanol hydrotrioxides are efficient sources of singlet oxygen; the yield of ¹О₂ reaches up to 58%.     

Analysis of solid solutions stability in scheelite-type molybdates and tungstates

Mutual solubility of bivalent metal molybdates and tungstates with scheelite structure was theoretically estimated by calculating formation enthalpies and the maximal decomposition temperatures of solid solutions at different temperatures. The theoretical stability of continuous solid solutions in binary systems of bivalent metal molybdates and tungstates was found to be higher than reported literature data. After cooling down continuous substitution solid solution should remain in following systems: CaMoО₄–CdMoО₄, SrMoО₄–MMoО₄ (M=Ba, Pb), BaMoО₄–PbMoО₄, SrWO₄–MWO₄ (M=Ca, Pb), and BaWO₄–PbWO₄. There is a probability that at room temperature in systems CaMoО₄–SrMoО_4, CaWO₄–PbWO₄, and BaWO₄–SrWO₄ the single homogeneity region may decompose to limited solid solutions. It was shown experimentally that a continuous series of scheelite-structure solid solutions M_1−xM^I_xТO₄ can be formed via citrate synthesis at temperatures below 500°С.     

О,О‐Dialkyl‐S‐(1,1‐dimethyl‐2‐oxoethyl)dithiophosphates: Synthesis and Reactions with n‐Nucleophiles

Hydrolysis of the new types of iminium salts was used to synthesize О,О‐dialkyl‐S‐(1,1‐dimethyl‐2‐oxoethyl)dithiophosphates or 2‐dialkoxythiophosphorylthio‐substituted aldehydes with carbon isochain. Reactions of aldehydes with N‐, N,N‐, and O,N‐nucleophiles gave new phosphorylated imines containing an acetal group at different positions, perhydro‐1,3‐diazol and oxazol with the diisopropoxythiophosphorylthio group in a side chain, and hydrazone of this aldehyde and diphenylphosphinylacetic acid hydrazide.     

Rearrangements and Tautomeric Transformations of Heterocyclic Compounds in Homogeneous Reaction Systems Furfural–Н<Subscript>2</Subscript>О<Subscript>2</Subscript>–Solvent

General information on the reactions of furfurals with hydrogen peroxide is given. We have discussed the Baeyer–Villiger rearrangement of furan 2-hydroxyhydroperoxides and tautomeric transformations with proton transfer of 2-hydroxyfuran and β-formylacrylic acid formed in a homogeneous reaction system furfural–Н₂О₂–solvent under the catalysis with the formed acids. The factors affecting these rearrangements and tautomeric transformations as well as their specificity in comparison with benzene type compounds, and the pathway of the reactions of furan aldehydes with Н₂О₂ in water have been analyzed. Ketoenol tautomerism of cyclic hemiacetal form of β-formylacrylic acid leading to its transformation into succinic anhydride has been described for the first time.     

Enthalpies of the formation and decomposition of hydrogen trioxide HOOOH in an aqueous solution

The enthalpies of the formation and decomposition of hydrogen trioxide are estimated from the heating curves of peroxide-radical condensates synthesized from gaseous O₂ + H₂ mixtures. Enthalpy of decomposition Н₂О₃(aq.) → Н₂О(liq.) + О₂(gas) is ?31.2 ± 1.5 kcal/mol, and enthalpy of formation Δ_fH(H₂O₃, aq.) =–37.5 ± 1.6 kcal/mol. Both values correspond to the temperature range of 240–265 K.     

Dithiophosphorylation of nerol and geraniol trimethylsilyl derivatives

Reaction of tetraphosphorus decasulfide with О-(cis- and trans-3,7-dimethylocta-2,6-dien-1-yl)-trimethylsilanes affords О,О-bis(cis- and trans-3,7-dimethylocta-2,6-dien-1-yl) S-(trimethylsilyl)dithiophosphates.     

<Subscript>N</Subscript>-alkyl-2-halo- and 2,2-dihaloaldimines in the Pudovik reaction

The use of N-alkyl-2-haloaldimines in the imine version of the Pudovik reaction, namely, in the reaction of imines with acid esters of phosphorus acids, much extended the synthetic potential of this reaction due to the fact that the primary addition and protonation product, having quite a mobile single hylogen atom, can undergo both spontaneous transformations and transformations involving other reagents. The reduction of the С–Hlg bond in N-alkyl-2-halo- and -2,2-dihaloaldiminium salts with О,О-dialkyl phosphorodithioic acids was observed for the first time.     

Electrosynthesis of Н<Subscript>2</Subscript>О<Subscript>2</Subscript> from О<Subscript>2</Subscript> in Gas Diffusion Electrodes Based on Black СН600

Furnace black СН600 was studied as a catalyst for electrosynthesis of Н₂О₂ from О₂ in a gas diffusion electrode in alkaline and acidic solutions. The texture properties of the starting black СН600 and gas diffusion electrodes (GDEs) based on it were determined by the low-temperature nitrogen adsorption (LTNA) method. The rate constants of Н₂О₂ decomposition on black and its mixtures with fluoroplast-4D in acidic and alkaline solutions of electrolyte were calculated. The process selectivity γ (the current fraction spent on the two-electron reduction of oxygen), kinetic parameters of oxygen reduction, and double-layer capacity of the СН600-based GDE were determined. Data on the kinetics of hydrogen peroxide accumulation during electrosynthesis from oxygen in СН600-based GDE in acidic and alkaline solutions were obtained.     

Electrosynthesis of Н<Subscript>2</Subscript>О<Subscript>2</Subscript> from О<Subscript>2</Subscript> in a Gas-Diffusion Electrode Based on Mesostructured Carbon CMK-3

Mesostructured carbon CMK-3 (Carbon Mesostructured by KAIST) synthesized by the template method is studied as the electrocatalyst for electrosynthesis of Н₂О₂ from О₂ in a gas-diffusion electrode (GDE) in alkaline and acidic solutions. The texture characteristics of the original material and its mixture with hydrophobizer (polytetrafluoroethylene) are studied by the method of low-temperature nitrogen adsorption. The rate constants for hydrogen peroxide decomposition on these materials in alkaline and acidic solutions are calculated. Kinetic parameters of oxygen reduction in alkaline and acidic solutions are determined as well as the capacitance of gas-diffusion electrodes based on mesocarbon. The selectivity of the electrocatalyst is estimated by finding the current fracture γ consumed in oxygen reduction to hydrogen peroxide. Data on the kinetics of hydrogen peroxide accumulation during electrosynthesis of Н₂О₂ from О₂ are obtained. The acidic solution of hydrogen peroxide with the concentration more than 3 M is obtained with the current efficiency higher than 80%.     

Reactions of diphenyl- and diethylphosphinodithioic acids with <Emphasis Type="Italic">N</Emphasis>-alkyl-2-haloaldimines in the synthesis of new P,S- and N,P,S-containing organic compounds

Diphenyl- and diethylphosphinodithioic acids, unlike the stronger О,О-dialkyl phosphorodithioic acids, react with N-alkyl-2-chloroaldimines at a 1: 1 ratio, following two pathways: nucleophilic substitution of chlorine in the primary salt by the phosphinothioylthio group and reduction of the cation of the primary salt on the C–Cl bond. Nucleophilic substitution contributes more in the case of the stronger diphenylphosphinodithioic acid, as well as in the case of a large excess of the starting chlorimine. N-Alkyl-2-bromoaldimines react only by a single pathway, specifically, reducing the cation of the primary iminium salt on the C–Br bond. New iminium salts were synthesized and converted into the corresponding aldehydes and imines. The aldehydes synthesized were converted into acetals and five-membered heterocyclic compounds.     

Catalytic Ozonation of Oxalic Acid in Aqueous Solution in the Presence of Manganese Ions

Kinetics and Catalysis - The kinetics of mineralization of oxalic acid Н2С2О4 under the action of ozone in acidic aqueous solution (С(НClО4) = 0.1 M, pH ~ 1)...     

Volume properties and refraction of aqueous solutions of bisadducts of light fullerene С60 and essential amino acids lysine,threonine, and oxyproline (С60(C6H13N2O2)2, С60(C4H8NO3)2, and С60(C5H9NO2)2) at 25°C

Concentration dependences of the density of aqueous solutions of bisadducts of light fullerene С₆₀ and essential amino acids are studied by pycnometry. Concentration dependences of the average molar volumes and partial volumes of components (Н₂О and corresponding bisadducts) are calculated for С₆₀(C₆H₁₃N₂O₂)₂–Н₂О, С₆₀(C₄H₈NO₃)₂–Н₂О, and С₆₀(C₅H₉NO₂)₂–Н₂О binary systems at 25°C. Concentration dependences of the indices of refraction of С₆₀(C₆H₁₃N₂O₂)₂–Н₂О, С₆₀(C₄H₈NO₃)₂–Н₂О, and С₆₀(C₅H₉NO₂)₂–Н₂О binary systems are determined at 25°C. The concentration dependences of specific refraction and molar refraction of bisadducts and aqueous solutions of them are calculated.

     

<Emphasis Type="Italic">N,N</Emphasis>-diethylanilinium complex with borodicitric acid: Synthesis and crystal structure

N,N-Diethylanilinium dicitratoborate [C₆H₅NH(C₂H₅)₂][(C₆H₆O₇)₂B] (I) has been synthesized for the first time. Single crystals has been synthesized in an aqueous solution to study the crystal structure of complex I by single-crystal X-ray diffraction. Crystals are triclinic, space group Р1 a = 9.6183(2) Å, b = 10.3153(3) Å, c = 13.7364(4) Å, α = 69.0304(12)°, β = 77.0394(13)°, γ = 89.5518(10)°, V = 1236.25(6) ų, Z = 2, ρ_calcd = 1.454 g/cm³. Structural units in a crystal of complex I are large complex dicitratoborate anions with a spirane structure and N,N-diethylanilinium cations. The crystal packing is a three-dimensional framework implemented via a system of hydrogen bonds like О–Н…О, О–Н…О, ОI, and N–Н…О.     

New titanium(IV) coordination compounds with 2-hydroxybenzyl alcohol derivatives used in the preparation of ultra-high molecular weight polyethylene

Russian Chemical Bulletin - A reaction of 2,4-bis(α,α-dimethylbenzyl)phenol with TiCl2(ОPri)2 and Ti(ОPri)4 was used to obtain the coordination compounds...     

Oxidation with CrO<Subscript>3</Subscript>·2Py of levoglucosenone and 1,3-dienes Diels-Alder adducts

Diels-Alder adducts of levoglucosenone with 1,3-butadiene, piperylene, and isoprene, and also some of their derivatives undergo allylic oxidation with CrО₃·2Py only in the case when the effect of a keto group or of another electron-acceptor group in the γ-position with respect to the double bond is removed.     

Electrical Conductivity,Thermal Expansion and Electrochemical Properties of Perovskites PrBaFe<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5 + δ</Subscript>

In order to evaluate applicability of mixed-conducting PrBaFe_2–xNi _x О_{5 + δ} perovskites for cathodes of solid oxide fuel cells (SOFCs), their crystal structure, thermal and chemical expansion, electrical conductivity and electrochemical behavior were studied. The solubility limit of nickel in PrBaFe₂O_{5 + δ} corresponds to x = 0.8. At x > 0.2, the disordered cubic phase transformed into the tetragonal phase. The maximum level of conductivity (50–120 S/cm) at the operating temperatures of SOFC was found for the composition with the maximum nickel content, PrBaFe_1.2Ni_0.8О_{5 + δ}. This material is also characterized by moderate thermal and chemical expansion relative to other ferrite-nickelates. The polarization resistance of a porous PrBaFe_1.2Ni_0.8О_{5 + δ} cathode in a cell with a protective Ce_0.6La_0.4O_2–δ layer and a solid electrolyte (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3–δ was ~0.9 Ohm cm² at a temperature of 1073 K, atmospheric oxygen pressure, and current density of–120 mA cm^–2.