Mechanism of oxidation of molybdovanadophosphoric heteropoly blues by molecular oxygen. Trivanadium heteropoly blue

The oxidation of a heteropoly blue (HPB) of the composition Na_xH_9-xPMo₉V₃O₄₀ with molecular oxygen has been studied by the method of catalytic vanadyl oxidation. It is shown that the reduction of an oxygen molecule requires the addition of a fourth atom of V(IV) in the form of a vanadyl ion to the heteropoly anion.

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: Na_xH_9-xPMo₉V₃O₄₀. , V(IV), .

     

A differential scanning calorimetric study of some phenol derivatives

Differential scanning calorimetry has been applied to derive the fusion enthalpies and entropies of series of mono and dimethylphenols, mono and dichlorophenols, and mono and dinitrophenols.

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Zusammenfassung DSC wurde verwendet zur Ermittlung der Schmelzenthalpie und Entropie der Reihen von Mono- und Dimethylphenolen, Mono- und Dichlorphenolen, Mono- und Dinitrophenolen.

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- , - , - .

     

Acid-base and catalytic properties of binary oxides in the oxidative dehydrodimerization of toluene

Acidity and basicity of binary oxide catalysts measured by the CO₂ and NH₃ thermodesorption method are compared with their catalytic activity in oxidative conversion of toluene. The rate of toluene dehydrodimerization is shown to increase with the catalyst basicity.

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CO₂ NH₃ . , .

     

Studies of transnitrilation mechanism in the presence of trifluoroacetic acid

A non-cyclic imide, an intermediate of transnitrilation, is shown to be formed through the step of unstable isoimide isomerization. The addition of a carboxy group of the acid to the cyano group has been studied. Interaction of acetonitrile with aliphatic carboxylic acids is suggested to follow a concerted but not a synchronous mechanism with prior formation of the N–H bond.

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, — — . . , , N–H.

     

Kinetics of water vapor adsorption by ion exchange polyacrylonitrile fibres

Kinetics of water vapor adsorption by ion exchange PAN fibres has been studied. Adsorption can be described by an exponential kinetic equation. Experimental results permit the assumption that the surface of the materials studied behaves as uniformly nonhomogeneous with more strongly expressed entropy nonhomogeneity, connected with cross-linking of the modified fibres. The dependence between the kinetic characteristics and the solubility of the materials in DMF shows that the main factor affecting unfavorably the adsorption kinetics is cross-linking. Increase of N-containing anion exchange groups reduces the effect of adsorption delay due to cross-linking.

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. , . , , , . , , - , . N- -- .

     

Oxidative stability of lubricants for dry circuit sliding contacts

The thin film oxidation resistance of isoparaffin and two polyol esters synthetic lubricants was studied by high pressure differential scanning calorimetry. The oxidation induction time of each lubricant was measured by isothermally heating the sample in an oxygen environment. Arrhenius plots were constructed to predict the service life of the lubricant at low temperatures. The results indicate that polyol esters exhibit better oxidative stability than isoparaffins.

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Zusammenfassung Mittels Hochdruck-Differential-Scanning-Kalorimetrie wurde die Dünnschicht-Oxydationswiderstandsfestigkeit von Isoparaffin- und zwei synthetischen Polyolesterschmiermitteln untersucht. Die Oxydationsinduktionszeit jedes Schmiermittels wurde durch isothermes Erhitzen der Probe in Sauerstoff gemessen. Zur Vorhersage der Lebensdauer der Schmiermittel bei niedrigen Temperaturen wurden die entsprechenden Arrhenius-Diagramme erstellt. Die Ergebnisse zeigen, dass Polyolester über eine bessere oxydative Stabilität verfügen als Isoparaffine.

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, . . . , , .

     

Oxidation with MnO2 supported on Y,FAU zeolite

MnO₂ supported on Na-Y,FAU prepared as described in a previous paper has been tested for selective oxidation of benzyl alcohol to benzaldehyde. Experimental results have shown that oxidation is selective and stoichiometric under the conditions used, but the adsorption of the substrate and/or the product on the zeolite support decreases the yield of benzaldehyde.

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MnO₂, Na–Y,FAU, , . . , , , / .

     

Alkylation of toluene with ethylene on HZSM-5

Alkylation of toluene with ethylene on unmodified large-crystal HZSM-5 has been studied in a flow system at 673 K, atmospheric pressure. The yield of ethyltoluenes increased and that of benzene and xylenes decreased with time on stream. This change in yields was accelerated by increasing the ethylene content of feed and by pretreating the catalyst with ethylene. Selectivity for toluene ethylation increase with increasing space velocity.

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HZSM-5 673 . - , . - - -. .

     

Kinetics of deuterium isotope exchange between thiophenol or t-butylthiol and i-propylthiol

The rate constants and activation energies of bimolecular deuterium exchange in the systems: C₅H₅SD+i-C₃H₇SH and t-C₄H₉SD+i-C₃H₇SH in dilute C₆H₁₂ solutions have been established. The concerted H-transfer inside the cyclic dimer with two H-bonds formed in these systems is probably the rate-limiting step. The rate constant for H-transfer inside the cyclic dimer is independent of the acidic properties of the thiols.

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: C₆H₅SD+i-C₃H₇SH -C₄H₉SD+i-C₃H₇SH C₆H₁₂. -, , , . .

     

Oxidation of trimethoxybenzenes to benzoquinones with hydrogen peroxide in the presence of heteropolyacid

Trimethoxybenzenes were oxidized to dimethoxy-p-benzoquinones in fairly good yields (50–60%) with hydrogen peroxide in the presence of heteropolyacid in the solvent of acetic or formic acid.

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-- (50–60%) , , .

     

Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al₂O₃ support.

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Al₂O₃ -, , . . ., , - Al₂O₃.

     

Partial oxidation of 1-butene on NiO?MoO3 catalysts supported on a HY ultrastable zeolite

The partial oxidation of i-butene on a series of Ni–Mo catalysts supported on a HY ultrastable zeolite has been carried out in a fixed bed, continuous flow reactor up to 380 °C. The changes in activity and selectivity has been correlated with the acidity of the catalysts, measured by pyridine adsorption-desorption.

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Ni–Mo, HY, 380°C. , - .

     

Catalytic desulfurization of ethanethiol over zinc-forms of NaX zeolites

Zinc exchanged zeolite X was found to catalyze effectively the dehydrosulfurization of ethanethiol. The catalytic activity correlated linearly with the degree of ion exchange and increased with the reaction temperature. The role of zinc cations in the reaction examined is discussed and suggestions concerning the reaction mechanism are put forward.

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X, Zn, . . .

     

State of copper ions, bond energy of oxygen and catalytic properties in hydrogen oxidation for a copper-magnesium system

The bond energy of surface oxygen in a copper-magnesium catalyst and its reactivity are shown to be greatly dependent on the structure of the nearer environment of copper ions. For catalysts prepared at low temperatures (773 K) this structure changes from a symmetrical square planar in CuO to an octahedral with various degrees of axial distortion depending on the copper content.

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, . , (773 ), CuO .

     

Catalytic oxidation of carbon monoxide by oxygen and nitrogen oxides on a copper-chromium oxide catalyst

The kinetics of CO oxidation by O₂, NO and NO₂ has been studied on a Cu–Cr-oxide catalyst. A comparison with the kinetics of the CO–N₂O interaction has been made. In all cases the reaction rate is described by the equation:r=k p _CO ¹ P _0x ⁰ . The oxidation of CO has been studied in the presence of different oxidants in the reaction mixture.

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CO , . CO . CO . CO .

     

Catalytic preparation of diacetone alcohol in controlled flow conditions

Catalytic preparation of diacetone alcohol from acetone was studied using strong basic ion exchangers as catalysts. A continuous process was carried out in an enlarged laboratory set-up with controlled flow rate. Experiments were performed with respect to experiment duration, temperature, flow rate, catalyst porosity and catalyst-acetone ratio. The quantity of DAA was determined by gas chromatography. The effects of temperature, catalyst porosity and catalyst-acetone ratio on the reaction course were significant in comparison with other parameters examined. An exponential dependence of C/A ratio on DAA yield was found.

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() , . . , , , /. . , / (/) . - /.

     

Study of reversible proton transfer from 2,2,2-trifluoronitroethane to amines by dynamic1H and19F NMR

The interaction between the weak CH-acid CF₃CH₂NO₂ and aliphatic amines has been studied by NMR in CDCl₃ and CFCl₃ solutions. It is shown that no measurable amounts of H-bonded complexes are formed. However, reversible proton transfer with the formation of ion pairs takes place. The kinetic parameters of this process have been determined.

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CH- CF₃CH₂NO₂ CDCl₃ CFCl₃. , , . .

     

Binding energy and reactivity of surface oxygen of cobalt molybdates

For the first time it was shown that cationic solid electrolyte — pyrex glass can be used for determining the binding energy of surface oxygen for binary catalysts of partial oxidation. On this basis the activity and selectivity of - and -CoMoO₄ are discussed.

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— . .

     

Enthalpimetric determinations with sodium hypobromit

The applicability of sodium hypobromite as a reagent in enthalpimetric determinations of various organic and inorganic compounds is reviewed. Using this method it is possible to determine various oxidizable nitrogen and sulphur compounds, e.g. ammonium salts, urea, -amino acids, sulphides, sulphites, thiosulphates, organic compounds with sulphidic sulphur, aromatic amines, mono- and polyphenols, and other compounds. Determinations are sufficiently precise and sensitive. The enthalpy changes of these reactions are approximately 10² to 10³ kJ mole^–1. Suggested determinations are advantageous due to their simplicity, quickness and possible automatization of measurements.

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Zusammenfassung Die Autoren geben einen Überblick zur Anwendung von Natriumhypobromit als Reagenz bei den enthalpimetrischen Bestimmungen verschiedener organischer und anorganischer Verbindungen. Der Einsatz dieser Methode ermöglicht die Bestimmung verschiedener oxidierbarer Stickstoff- und Schwefelverbindungen, wie z.B. Ammoniumsalze, Karbamid, -Aminosäuren, Sulfide, Sulfite, Thiosulfate, organische Verbindungen mit Sulfidschwefel, aromatische Amine, ein- und mehrwertige Phenole und andere Verbindungen. Die Bestimmungen sind genügend genau und empfindlich. Die Enthalpie-Änderungen dieser Reaktionen liegen in der Größenordnung von 10² is 10³ kJ Mol^–1. Die vorgeschlagenen Bestimmungen sind wegen ihrer Einfachheit, Schnelligkeit und der Möglichkeit der Automatisierung der Messungen vorteilhaft.

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Résumé Les auteurs examinent l'emploi de l'hypobromite de sodium comme réactif pour le dosage enthalpimétrique de divers composés organiques et inorganiques. Par cette méthode il est possible de doser différents composés azotés et sulfurés, par ex. les sels d'ammonium, l'urée, les -amino-acides, les sulfures, les sulfites, les thiosulfates, les composés organiques sulfurés, les amines aromatiques, les phénols mono et polyvalents et d'autres composés. Les dosages sont suffisamment précis et sensibles. Les variations d'enthalpie de ces réactions sont de l'ordre de 10²-10³ kJ · mol^–1. Les dosages proposés ont l'avantage d'être simples, rapides et susceptibles d'être automatisés

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, , . - , : , , -, , , , , , . . 10² 10³ /. , .

     

On the structure of surface active centers on CuO

It has been established that surface active centers on CuO can be associated with its surface defects, i.e. surface exits of twinning and screw dislocations where highly reactive oxygen and CO can be coordinated.

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, , CO.