Исследование роли фосфиновых комплексов никеля различных степеней окисления в каталитической димеризации олефинов

Ni(II), Ni(I) Ni(O) . , , , Ni(O) Ni(I) - Ni(I) Ni(II) Ni(O).

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The interaction of organoaluminium compounds with phosphine complexes of Ni(II), Ni(I) and Ni(0) has been studied under the conditions of catalytic propylene dimerization. The active complexes are formed from Ni(II) compounds, the regeneration of the latter is ensured by repeated reduction, oxidation of Ni(0) to Ni(I), and by disproportionation of Ni(I) into Ni(II) and Ni(0).

     

Kinetics and mechanism of TI(III) oxidation of cellobiose in acidic medium

TI(III) oxidation of cellobiose in the presence of H₂SO₄ in aqueous acetic acid is first order in each reactant and is acid catalyzed. TI(OAc) ₂ ⁺ is the active species. Products identified are gluconic acid and glucose. A mechanism consistent with the temperature, solvent, acidity and salt effects is been proposed.

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TI(III) H₂SO₄ . TI(OAc) ₂ ⁺ . . , , , .

     

Measurement of thermal constants of calcium chromite by Laser Flash method

Calcium chromite, CaCr₂O₄, was prepared and its purity and stoichiometry were ascertained by chemical analysis and X-ray diffraction methods. The thermal diffusivity, specific heat capacity and thermal conductivity of calcium chromite were measured by Laser Flash method using an Ulvac-Sinku Riko TC-3000 series instrument in the temperature range of 298 to 1100 K. The heat capacity data were utilised to calculate the thermodynamic parametersenthalpy increments, entropy increments and free energy increments—in the above temperature range.

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Zusammenfassung Kalziumchromit, CaCr₂O₄, wurde hergestellt und seine Reinheit und stöchiometrische Zusammensetzung mit Hilfe chemischer Analyse und Röntgendiffraktionsmethoden ermittelt. Anhand eines Ulyac-Sinku Riko TC-3000 Gerätes wurde mit Laser Flash Verfahren die Temperaturleitfähigkeit, die spezifische Wärmekapazität und die Wärmeleitfähigkeit von Kalziumchromit im Temperaturbereich 298–1100 K bestimmt. Die Wärmekapazitätsdaten wurden zur Berechnung der thermodynamischen Größen (Enthalpie-, Entropie-, Freie Energieänderung) in obigem Temperaturbereich benutzt.

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CaCr₂O₄, . , - TC-3000, 298–1100K , . , , .

     

Characteristics and surface morphology change of modified PtRh 10 gauze of HCN synthesis

The modification of PtRh10 gauze catalysts by coating their surfaces with a thin film of PtRh/Al₂O₃ is reported. The investigation of the activity, selectivity and morphological change of the surface of the catalyst for standard gauzes and those covered with a thin film, applied in the HCN synthesis is deseribed.

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PtRh 10 PtRh–Al₂O₃. , HCN.

     

Reactions in the combustion of hydrocarbons

Combustion of LPG produces carbon dioxide directly up to a temperature of 525°C. In addition, the formation of unsaturates is observed at temperatures above 550°C as a result of oxidative dehydrogenation and subsequent combustion of unsaturates to carbon dioxide at temperatures higher than 575°C.

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525°C. , 550°C . 575°C .

     

Effect of addition of intermetallic componds on the catalytic activity of La2CuO4

Decomposition of nitrous oxide has been studied on pure La₂CuO₄, La₂CuO₄ with 5 wt.% CaNi₅ and La₂CuO₄ with 5 wt.% NiO in the temperature range 200–480°C at 200 Torr initial pressure of reactant gas. The addition of 5 wt.% CaNi₅ decreases the energy of activation drastically in comparison with La₂CuO₄. The results are explained on the basis of the dispersity of Ni/NiO on La₂CuO₄.

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La₂CuO₄ 5.% CaNi₅ 5 .% NiO , 200–480°C 200 . 5 . % CaNi₅ . Ni/NiO La₂CuO₄.

     

Oxygen adsorption on silver-gold alloy

Oxygen adsorption on Ag/Au alloys has been studied by field-emission microscopy (FEM). A decrease in the silver concentration of alloy is accompanied by a drastic fall in its ability to absorb oxygen. Using the interacting bonds method (IBM), the adsorption heat of atomic oxygen on the (100) plane of the silver-gold alloy has been calculated.

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. , . (100) .

     

NMR Study of the Stoichiometry, Stability, and Ligand Interchange of Silver Ion-Hexathia-18-crown-6 Complex in Binary Dimethyl Sulfoxide Solvent Mixtures at 300 K

Proton NMR was used to study the complexation reaction between silver ion and hexathia-18-crown-6 in a number of binary mixed solvents of dimethyl sulfoxide with acetonitrile and methanol. Formation constants for the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. The influence of solvent composition on the stability of the resulting complex is discussed. The exchange kinetics of Ag⁺-hexathia-18-crown-6 in 70-30 wt.% dimethyl sulfoxide-acetonitrile and 75-25 wt.% dimethyl sulfoxide-methanol were studied by proton NMR line-shape analysis. In both solvent mixtures, the exchange of thiacrown ether between the free and complexed sites was found to proceed via a dissociative pathway. The exchange rates and the activation parameters E _a, H , S, and G for the ligand exchange were determined and the influence of solvent properties on these parameters discussed.     

Thermal properties of Jojoba wax

The thermo-oxidative stability of Jojoba wax (Simmondsia chinensis) was studied by differential scanning calorimetry in a dynamic oxygen atmosphere. The thermo-oxidation activation energy (Ea) was calculated by determining the maximum reaction temperature (Tm) at different heating rates (Hr) and using mathematical models previously proposed for dynamic systems. The value obtained was 21.84 Kcal/mol. The oxidation enthalpiesH _ox were also calculated and a lineal relationship was found with the square root of the heating rate and the initial temperature of thermo-oxidation

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Zusammenfassung Die thermooxidative StabilitÄt von Jojoba-Wax (Simmondsia chinensis) wurde durch Differential-Abtastkalorimetrie in dynamischer SauerstoffatmosphÄre untersucht. Die Aktivierungsenergie der Thermooxidation (Ea) wurde durch die Bestimmung der maximalen Reaktionstemperatur (Tm) bei verschiedenen Aufheizgeschwindigkeiten (Hr) unter Anwendung der vorhergehend für dynamische Systeme vorgeschlagenen mathematischen Modelle berechnet. Der erhaltene Wert betrug 21.84 Kcal/Mol. Die OxidationsenthalpienH _ox wurden ebenfalls berechnet und lineare ZusammenhÄnge mit der Quadratwurzel der Aufheizgeschwindigkeit und der Anfangstemperatur der Thermooxidation wurden gefunden.

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Résumé On a étudié, par analyse calorimétrique différentielle dans une atmosphère dynamique d'oxygène, la résistance à l'oxidation thermique de la cire Jojoba (Simmondsia chinensis). On a calculé l'énergie d'activation (Ea) de l'oxydation thermique en déterminant la température maximale (Tm) de la réaction à diverses vitesses de chauffage (Hr) et en utilisant les modèles mathématiques déjà proposés pour des systèmes dynamiques. La valeur obtenue est 21.84 kcal/mole. On a calculé également les enthalpies d'oxydation (H_ox) et on a trouvé des corrélations linéaires entre les racines carrées de la vitesse de chauffage et la température initiale de l'oxydation thermique.

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Jojoba (Simmondsia chinensis) . - (E _a) ( _m) , . 21.84 /. (H _ok) .

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This work has been partially supported by the Consejo Nacional de Ciencia y Technología and the Comisión Nacional de las Zonas Aridas.     

Hysteresis of thermogravimetric curves of nickel catalysts for methane conversion in CH4+CO2 mixture

Characteristic peculiarities of the supercarbonization peak, i. e. the effect of carbon accumulation on the catalyst surface and its subsequent removal under heating in the CH₄+CO₂ mixture have been studied. Hysteresis of thermogravimetric curves in the heating/cooling cycle has been established.

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— . -.

     

Thermal stability of epoxy adhesives

A study was made of the thermal stability of epoxy compounds which were unfilled or contained metallic fillers such as aluminium dust, aluminium flakes, powdered bronze, powdered brass and silver flakes. The properties of the compounds were modified by the use of various hardeners.

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Zusammenfassung Es wurde die thermische StabilitÄt ungefüllter und gefüllter Epoxidkompositionen untersucht. Als metallische Füllstoffe wurden Aluminiumpulver und -flocken, Messing- und Bronzpulver sowie Silberflocken eingesetzt. Die Eigenschaften dieser Kompositionen wurden mit verschiedenen HÄrtern modifiziert.

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, , , . .

     

Reactions of α-halo-α, β-unsaturated aldehydes with secondary amines

Reactions of 2-halo-2-alkenals R(R)C=CX-CHO with secondary amines R₂NH occur asipso-substitution of the halogen atom, along with fragmentation and condensation, yielding 1,2-diaminoethenes R₂NCH=CHNR₂, carbonyl compounds RC(O)R, 1,3-bis(amino)-2-haloolefins R(R)C(NR₂)CX=CHNR₂, and formamides R₂NCHO. The ratio between the competing reactions depends on the structure of the starting compounds and the experimental conditions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp, 135–138, January, I996.     

Interaction of cyclodextrins with drugs. Chromatographic investigation using a cyclodextrin bonded-phase and its application to chiral separations

Summary The interaction between cyclodextrin and the drug (1R,2S,3S,4S)-(5Z)-7-(3-((phenylsulfonyl)amino)bicyclo[2.2.1]hept-2-yl)hept-5-enoic acid ((+)-S-145), was studied using -, -, and -cyclodextrin bonded-phase columns. Retention behavior of (+)-S-145 on these columns revealed that the strength of inclusion was -cyclodextrin. Interaction between -cyclodextrin and (+)-S-145 was found to increase as the proportion of carboxylic ion in the (+)-S-145 molecule increased. Comparison of binding capacities of these bondedsilica gels obtained by frontal analysis and surface coverage indicated that availability of the immobilized - and -cyclodextrin was 20–25%. The synthesized -cyclodextrin bonded-phase column was superior to that of commercial columns in terms of chiral separation of (±)-S-145. A typical usage of the -cyclodextrin column is discussed for separation of (±)-S-145 in plasma samples.     

Selective oxidation and ammoxidation of isobutene over mixed oxides of tin and antimony

The oxidation and ammoxidation of isobutene were studied over mixed oxides SnO₂/Sb₂O₄ as catalysts, in a pulse reactor between 598 and 698 K. From the point of view of methacrylonitrile production the catalysts of compositions SnSb=4–51 behaved most appropriately at the optimum reaction temperature of 673 K. Below this temperature the production of methacrolein was preferred, even in the presence of ammonia, whereas at higher temperatures total oxidation prevailed.

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SnO₂/Sb₂O₄, 598 698 . SnSb=4–51 , 673 . , , .

     

Kinetics of catalytic hydrolysis of tetraethoxysilane by polycomponent solutions of neutral salts

The effect of salt concentrations on the hydrolysis kinetics in three-component systems containing tetraethoxysilane and aqueous solutions of sodium, neodymium and lead nitrates has been shown. A generalized model for the synthesis of polycomponent hydrolytes is suggested, which permits to predict the conditions to prepare compositions with specified characteristics.

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, , . , .

     

The structure of xanthoceras saponin

Summary It has been established that xanthoceras saponin is O--arabopyranosyl-(1 4)-[O--galactopyranosyl-(1 6)-O--glucopyranosyl-(1 3)]-O--glucuronopyranosyl-(1 3)-gypsogenin.Institute of Chemistry, Academy of Sciences of the Moldavian SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 442–444, July–August, 1971.     

Selective hydrogenation of fatty oils on alloyed Ni?Al catalysts. II. Optimal reaction conditions

The previously suggested kinetic model permits to predict that maximum selectivity towards olein is attained under the limiting diffusional resistance with respect to hydrogen. This conclusion is confirmed by the experimental data obtained in a fixed catalyst bed reactor. Some recommendations to intensify industrial processes are given.

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, . , . .

     

XPS study of ethylene adsorption on Ir (110)

The state of adsorption layers and adsorption kinetics of C₂H₄/Ir (110) at 300–1000 K has been studied using XPS method.

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C₂H₄/Ir (110) 300–1000 K.

     

CO hydrogenation on a highly loaded Rh/TiO2 catalyst and the influence of strong metal-support interaction

The CO hydrogenation on a highly loaded (25 wt.%) Rh/TiO₂ catalyst was investigated after reduction at 573 K and 723 K. Chemisorption measurements show that the Rt/TiO₂ ratio is in the SMSI state after the high temperature reduction. The catalytic activity is significantly lower in the SMSI state than after reduction at low temperature. The selectivity of CO hydrogenation is changed in the SMSI state to higher hydrocarbons

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CO Rh/TiO₂ (25 .%) 573 723 . , Rh/TiO₂ . , , .