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. , , . .

     

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

     

Applications of thermal analysis

This review paper outlines some current developments in thermal analysis. The current status of standard methods, in particular those issued by the American Society for Testing and Materials (ASTM), using thermal analysis techniques are discussed. In the second place a simple method for the determination of the oxidative stability of polyethylene by DTA is reviewed. Finally the paper surveys some of the more recent work being carried out in fossil fuels and fuel oils.

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Zusammenfassung Dieses Referat umreisst einige zeitgemässe Entwicklungen der Thermoanalyse. Es wird der derzeitige Stand der Standardmethoden besprochen, besonders derjenigen, die durch die American Society for Testing + Materials (ASTM) veröffentlicht wurden, und die ein thermoanalytisches Verfahren verwenden. In zweiter Reihe wird eine einfache Methode zur Bestimmung der oxydation Stabilität des Polyäthylens mittels DTA bekanntgemacht. Zum Schluss übersieht die Arbeit einige neuere Arbeiten, die an festen Heizmaterialien und Heizölen durchgeführt wurden.

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. , , , ASTM. ' . , .

     

Catalytic autooxidation of hydroquinone in the presence of chelate complexes of transition metals

Autooxidation of hydroquinone was studied in the presence of Co and Cu complexes with salene, decamethyl-octadehydrocorrine, corrine and o-phenanthroline as ligands in aqueous solution and in protic and aprotic solvents. A possible mechanism of the catalytic action of some active complexes is discussed.

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, Co, Cu , , - . .

     

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), .

     

Temperature dependence of the initial quantum yield of oxygen photoadsorption on zinc oxide

The initial quantum yield of photoadsorption at =365–577 nm is shown to decrease with the temperature increase. Experimental data are partly accounted for by the temperature shift of the long wavelength edge of the fundamental absorption band that is of low activity in oxygen photoadsorption.

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, 365–577 . , .

     

Energetic state of hydrogen on Os-black

Hydrogen adsorption on Os-black has been studied by the TPD method in the range from –85 to 450°C. Energetic inhomogeneity of hydrogen chemisorbed at adsorption temperatures of 150 to 450°C has been elucidated.

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OS (–85)–450°C. , 150 450°C.

     

Kinetics of oxidation of methanol by chlorine dioxide

The kinetics of oxidation of methanol by chlorine dioxide has been investigated at 35 °C. The reaction is first order with respect to both substrate and chlorine dioxide. Molecular chlorine dioxide is the principal oxidant. The influence of various factors, e.g. ionic strength, inorganic salts, D₂O and temperature on the initial rate has been studied. The activation parameters have been calculated and a mechanism involving hydride abstraction has been suggested.

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35 °C. , . . , . , , D₂O , . , .

     

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 . , .

     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Monohalogenobenzoylhydrazones VI. New antimony(III) complexes with monochlorobenzoylhydrazones of 2-furaldehyde, 2-pyrrolaldehyde and 2-thiophenaldehyde as ligands

The antimony(III) trihalides, SbX₃ (X=Cl, Br and I), react with the title ligands to give the compounds SbX₃L, where L=benzoyl- and monochlorobenzoylhydrazones of 2-furaldehyde (FBHH and FClBHH), 2-pyrrolaldehyde (PBHH and PClBHH) and 2-thiophenaldehyde (TBHH and TClBHH). The characterization of the new species was based on their elemental analyses, spectral data (IR and UV-Vis) and thermal studies. The ligands appear to offer two coordination sites (the carbonyl and azomethine groups) and perhaps a third one (the heteroatom of the heterocyclic ring). The thermal decompositions of the studied complexes proceed via one or three stages, the number of stages depending on the nature of both the hydrazones and the halogens. The structures proposed for the investigated complexes are either pseudo- or distorted octahedral.

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Zusammenfassung Antimon(III)-trihalogenide, SbX₃ (X=Cl, Br und I) reagieren mit den Titelliganden und liefern Verbindungen der allgemeinen Formel SbX₃L (L=Benzoylbzw. Monochlorobenzoylhydrazon von 2-Furfuraldehyd (FBHH und FClBHH), von 2-Pyrrolaldehyd (PBHH und PClBHH) und von 2-Thiophenaldehyd (TBHH und TClBHH). Die neuen Verbindungen wurden mittels Elementaranalyse, Spektraldaten (IR und UV) sowie thermischen Untersuchungen beschrieben. Zwei Koordinationsstellen scheinen von den Liganden bevorzugt zu sein: die Carbonylund die Azomethingruppe. Eine dritte könnte das Heteroatom des heterocyclischen Ringes sein. Die thermische Zersetzung der untersuchten Komplexe vollzieht sich in Abhängigkeit von der Natur der Hydrazone und der Halogene in einem oder in drei Schritten. Als Struktur für die untersuchten Komplexe wird eine pseudo-oder verzerrte oktaedrische Struktur vorgeschlagen.

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SbX ₃ (X=Cl, Br, I) - , 2- 2- , SbX ₃ L. , ( ), . , , . . .

     

Effect of vanadium content on the character of acidic sites on V2O5/Al2O3 catalysts

By IR spectroscopy and TPD the effect of vanadium content on the relative proportion of strongly acidic sites of V₂O₅/Al₂O₃ catalyst was studied.

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- - V₂O₅/Al₂O₃.

     

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- -- .

     

Thermal investigation of inhibition of polybismaleimide polymerization

DTA and DSC data revealed that the use of heteropoly compound additives allows an increase in the temperature of polybismaleimide radical polymerization by 20–60 deg in comparison with the value for the initial olygomer. TG data showed that in the presence of certain amounts of the inhibitor the polymer thermoresistance does not decrease. The range of effective concentration of the inhibitor is 1–5 wt.%.

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Zusammenfassung Nach DTA und DSC-Befunden kann die Anwendung von Zusätzen von Heteropolyverbindungen die Polymerisationstemperatur um 20–60° erhöhen. Nach TG-Ergebnissen nimmt die Wärmebeständigkeit des Polymers in Gegenwart kleiner Inhibitormengen nicht ab. Der Inhibitor wirkt in einer Konzentration von 1–5 Gew.%.

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, 20–60° . , . 1–5 .

     

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.

     

XPS studies of the surface of Sn?Sb?O catalysts

Electronic state of the cations of Sn–Sb catalysts has been investigated by the XPS method. The established change in the charge of tin and antimony ions is ascribed to the interaction between catalyst components during its formation. It has been found that the surface of Sn–Sb–O catalysts accumulates antimony, which accounts for their high selectivity in partial oxidation of olefin.

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-- - . , . Sn–Sb–O - , .

     

Problems of the characterization of thermoanalytical processes by kinetic parameters

On the basis of many experiments and theoretical reflections, the authors showed earlier that the courses of non-isothermal analytical curves are strongly influenced by the experimental conditions, and therefore the sense of kinetic parameters calculated from these curves is fictitious and their determination is uncertain.In the present work some further problems of this question are discussed. It was found that with combinations of strongly differing parameters nearly identical TG curves can be produced, and this situation cannot be improved even by orthogonal polynomial transformation. Further integral methods, using linearization, the estimation of the parameters is poor.The model transformed according to the conditions of the quasi-isothermal-quasiisobaric technique leads to contradictions, unambiguously showing the correlation existing between the parameters.

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Zusammenfassung Aufgrund zahlreicher Versuche und theoretischer Erwägungen hatten die Autoren früher gezeigt, daß der Verlauf nicht isothermer analytischer Kurven stark von den Versuchsbedingungen beeinflußt wird und deshalb die Bedeutung der aufgrund dieser Kurven berechneten kinetischen Parameter fiktiv und ihre Bestimmung unsicher ist.In der gegenwärtigen Arbeit werden einige weitere Probleme dieser Frage erörtert. Die Autoren fanden, daß mit Hilfe von Kombinationen stark verschiedener Parameter nahezu identische TG-Kurven hergestellt werden können und daß dieser Tatsache selbst durch orthogonale Polynomtransformation nicht abgeholfen werden kann. Weiter wurde gefunden, daß mit Hilfe von Integralmethoden unter Anwendung von Linearisierung erhaltene Schätzungen der Parameter ungenau sind.Das den Bedingungen der quasi-isothermen—quasi-isobaren Technik entsprechend transformierte Modell führt zu Widersprüchen, welche die zwischen den Parametern bestehenden Beziehungen eindeutig zeigen.

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Résumé A partir de nombreuses expériences et réflexions théoriques, les auteurs avaient démontré auparavant que l'allure des courbes TG non isothermes était fortement influencée par les conditions d'expérience. Pour cette raison, la signification des paramètres cinétiques calculés à partir de ces courbes était fictive et leur détermination incertaine.Dans le présent travail les auteurs discutent quelques autres problèmes sur cette question. En se servant de combinaisons de paramètres fortement différents on peut produire des courbes TG presque identiques et cette situation ne peut pas être améliorée même par transformation polynomiale orthogonale. En outre, on a trouvé qu'à l'aide de méthodes par intégration et par linéarisation, l'estimation des paramètres est mauvaise.Le modèle transformé selon les conditions de la technique quasi isotherme — quasi isobare entraîne des contradictions qui indiquent, sans équivoque, les corrélations existant entre les paramètres.

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, , , , . . , . , , , . , , , .

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The authors wish to thank Prof. E. Pungor for valuable remarks in this work.     

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. -, , , . .

     

Reaction mechanism and principles of choosing catalysts for selective oxidation at C?H bonds

Reaction mechanism for selective oxidation of organic compounds at C–H bonds is discussed. The criteria of selecting catalysts for these reactions have been formulated; 1) fast heterolytic activation of C–H bonds; 2) relatively slow primary activation of oxygen; 3) fast diffusion of oxygen vacancies; 4) fast electron transfer from the adsorbed substrate to catalyst.

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C–H . : 1) C–H ; 2) ; 3) ; 4) .