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) .

     

FTIR investigation of the structure of vanadium oxides on ZrO2 and oxidation of toluene on it

The oxidation of toluene has been studied on V₂O₅/ZrO₂ by both FTIR spectroscopy and pulse method. The results suggest that Lewis-acidic sites play a significant role in the formation of benzaldehyde from toluene.

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V₂O₅/ZrO₂ - , . .

     

Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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, . : > > > . .

     

Das System KNbO3-Nb2O5

Zusammenfassung Das System KNbO₃–Nb₂O₅ wurde mit thermoanalytischen, dilatometrischen und röntgenographischen Methoden neu untersucht. Acht ternäre Verbindungen werden im Bereich von 0–50 Mol-% K₂O gefunden. Nur K₄Nb₆O₁₇ schmilzt kongruent, alle anderen zersetzen sich peritektisch. Bei den beiden niobreichaten ternären Verbindungen handelt es sich um Hochtemperaturphasen, die sich erst oberhalb 1273 bzw. 1551 K bilden. Drei der acht Verbindungen wandeln sich mit steigender Temperatur in ihre Hochtemperaturmodifikation um.

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The KNbO₃-Nb₂O₅ system was studied by thermal analysis, dilatometry and X-ray techniques. Eight ternary compounds were found in the range from 0 to 50 mol% K₂O. Only K₄Nb₆O₇ was found to melt congruently, the other compounds decomposed peritectically. For the two ternary compounds with the highest percentage of niobium high-temperature phases were observed which were formed only above 1273 and 1551°, respectively. Three of the compounds studied transformed into their high temperature modifications on heating.

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, $ KN₃-Nb₂O₅. 0 50 % . , K₄Nb₆O₇ , $ . $ $ 1273 1551°. $ $ .

     

Kinetics of ion exchange sorption of phosphate

The kinetics of phosphate sorption on Amberlite IRA-400 has been studied as a function of temperature, nature of counterions, at two different concentrations. The film and particle diffusion coefficients and the activation parameters of the process are calculated.

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IRA-400 , . .

     

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. , , . .

     

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 , , - . .

     

Infrared study of the interaction of nitric oxide with CuY zeolites

Infrared studies of the interaction of NO with CuY–A zelites have been made over the temperature range from –100°C to 400°C. Several forms of NO adsorption have been found, in particular, a stable cis-dimer at low temperatures.

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- (–100+400°C) NO CuY–A . NO, ë - .

     

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. ' . , .

     

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 , . , .

     

Thermal decomposition of 5-Nitro-2-Furaldehyde Semicarbazone

Nitrofurazone, 5-nitro-2-furaldehydesemicarbazone, pharmaceutical compound, has been synthesized and its thermal behaviour studied by DTA, DSC and TG. The resulting thermoanalytical curves, showing that the maximum change in mass occurred at 516.5 K, with a 67% weight loss, are in good correlation with the enthalpy of the decomposition reaction, 326.93 kJ mol^–1. On the basis of the results, it is possible to establish the mechanism of the thermal decomposition and to acquire information on the stability of the analyzed organic compound, 5-nitro-2-furaldehydesemicarbazone.

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Zusammenfassung Das Arzneimittel Nitrofurazon (5-Nitro-2-furaldehyd-Semicarbazon) wurde synthetisiert und dessen thermisches Verhalten mittels DTA, DSC und TG untersucht. Die erhaltenen thermoanalytischen Kurven, die einen Gewichtsverlust von 67 Gew.-% mit maximaler Geschwindigkeit der Gewichtsabnahme bei 516,5 K zeigen, sind in guter Übereinstimmung mit der Enthalpie der Zersetzungsreaktion von 326,93 kJ·mol^–1. Aus den Versuchsergebnissen können der Mechanismus der thermischen Zersetzung abgeleitet und Informationen über die Stabilität von 5-Nitro-2-furaldehyd-Semicarbazon erhalten werden.

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, — 5-. , (67%) 516,5 , , 326,93 ·^–1. .

     

Inhomogeneity of strong Lewis acid centers on Al2O3 surface

Specificity of the bands at 1630–1620 cm^–1 in IR spectra of coordinatively bonded pyridine has been studied. Three strong Lewis-type acid centers have been revealed on Al₂O₃ surface.

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- 1630–1620 ^–1.

     

Effect of reduction temperature on the dehydrocyclizing activity of pure chromia and chromia containing K2O and CaO

The dehydrocyclization of n-heptane at 520–550°C over pure chromia and chromia with added CaO and K₂O (5 wt.% each) has been investigated. Introduction of an alkaline additive into Cr₂O₃ decreases markedly the yield of toluene. Raising of the reduction temperature of alkali-containing samples from 550 to 700°C results, in contrast to pure Cr₂O₃ and chromia-alumina systems, not in diminished, but in increased yields of toluene, the activity enhancement being particularly pronounced for the CaO-containing catalyst. These increased activities cannot be correlated either with variations in specific surface area or changes in the content of Cr⁶⁺ during subsequent oxidation, and presumably should be ascribed to more extensive catalyst reduction at higher temperatures.

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- 520–550° CaO K₂O ( 5% .). Cr₂O₃ . 550° 700° , Cr₂O₃ , , , CaO. , , .

     

Ein Beitrag zur thermischen Stabilität der Clathratverbindungen der Doppelcyanide in Abhängigkeit von ihrer Struktur

Zusammenfassung Die thermische Zersetzung zweier Hofmann'scher Clathratverbindungen, sowie der Verbindung Cd(NH₃)₂Hg(CN)₄·2 C₆H₆ wurde mittels des Derivatographen untersucht. Diese Clathratverbindungen sind bezüglich ihrer Struktur verschieden. Die Clathrate des Hofmann'schen Typs sind von höherer Stabilität. Die Gründe hierfür werden erörtert.

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The thermal decompositions of two Hofmann's clathrate compounds and the compound Cd(NH₃)₂Hg(CN)₄ · 2 C₆H₆ have been investigated by means of the derivatograph. These clathrate compounds are, as for their structure, different. Clathrate of the Hofmann's types represent the higher stability. The reasons are discussed in this paper.

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Résumé On a étudié, à l'aide d'un Derivatograph, la décomposition thermique de deux clathrates de type Hofmann ainsi que du composé Cd(NH₃)₂Hg(CN)₄·2 C₆H₆. Les clathrates étudiés possèdent des structures différentes. Les clathrates de type Hofmann sont les plus stables. Les raisons en sont discutées dans la présente communication.

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, 1,3,5,7--1,3,5,7- (), 1,5--3,7--1,3,5,7- (DADN), 1,5--3,7- -1,3,5,7- (D), 1,3,5--1,3,5- (-) 1,5--3,7- -1,3,5,7- (DNPT). , , DADN RDX . , R- DNPT, , . DPT.

     

Recent advantages in thermal analysis instrumentation

Curing and decomposition of a phenolic resin is studied by simultaneous thermal analysis (STA) and mass spectrometry (MS) to get quantitative and qualitative information on the reactions. The influence of the heating rate and the curing mass loss of the same material is measured with a symmetrical micro thermobalance. A high temperature DSC apparatus is used to determine the specific heat of a glass ceramic. Poco graphite is used for expansion calibration measurements with a new dilatometer up to 2000 °C.

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Zusammenfassung Mittels simultaner Thermoanalyse (STA) und Massenspektroskopie (MS) wurden Vernetzung und Zersetzung von Phenolharzen untersucht, um so quantitative und qualitative Erkenntnisse über die entsprechenden Reaktionen zu erlangen. Der Einfluß der Aufheizgeschwindigkeit und des Vernetzungsmassenverlustes desselben Stoffes wurde mit einer Mikrothermowaage gemessen. Zur Bestimmung der specifischen Wärme einer Glaskeramik wurde ein Hochtemperatur-DSC Gerät verwendet. Zu Ausdehnungskalibrationsmessungen bis zu 2000° mit einem neuen Dilatometer wurde Pocographit verwendet.

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- . . . 2000 .

     

Ligand exchange between bis-acetylacetonato cobalt (II) and organotin compounds SnR2Cl2 (R=Ph, Et), I. NMR identification of exchange products in the Co(AA)2?SnPh2Cl2 system

NMR studies of the interaction between bis-acetylacetonato Co(II) and organotin compound SnPh₂Cl₂ (Ph=C₆H₅ ^–) in chloroform solutions with pyridine additive have revealed ligand exchange between the initial components to form Co(II) and Sn(IV) complexes with different numbers of ligands.

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Co(II) SnPh₂Cl₂ (Ph=C₆H₅ ^–). , Co(II) Sn(IV) .

     

The use of temperature to simplify formose sugar composition

Form ose reaction, the Ca(OH)₂ catalyzed condensation of HCHO to a complex mixture of sugars, does not lose its autocatalytic nature at 98°C. The induction period is 15 sec, and then, at 18% total HCHO conversion, there was a period of approximately 3 sec duration in which the reaction had produced C₆ sugars at 84.3 wt.% selectivity. Glucose amounted to 90% of those sugars, and no branched sugars were detected. Conversion was complete within 3 min. The simple nature of the product was lost at lower temperatures or higher conversions.

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— HCHO, Ca(OH)₂, 98°C. 15 , 38%- HCHO 3 , C₆ 84,3 . %. 90%, . 3- . .

     

Reactivity of oxidized substances and its correlation with catalyst properties in deep oxidation reactions

In terms of the donor-acceptor interaction concept /1/ the relative reactivity (RR) of organic and inorganic compounds and its correlation with catalyst properties in deep oxidation reactions are treated. RR and relative activity of the catalysts are shown to change depending on the predominant character (acceptor or donor) of reactant-catalyst interaction.

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- /1/ (OPC) . , OPC .

     

A gradientless flow microreactor

A simple flow microreactor can perform as a gradientless microreactor under suitable conditions so that, thanks to molecular diffusion, the reactant concentration is leveled out considerably. This was demonstrated on the basis of a mathematical analysis of the reactant concentration distribution in a flow reactor and the observation was confirmed experimentally. A simple flow microreactor was designed and its gradientless property was verified using carbon dioxide hydrogenation as a test reaction.

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. . , . , .