Kinetic model and mechanism for selective hydrogenation of acetylene alcohols

A complex approach to the development of kinetic models in terms of the joint kinetic and physicochemical methods is suggested. To establish kinetic models for the hydrogenation of C₅, C₁₅ and C₂₀ acetylene alcohols on a modified Pd/Al₂O₃ (0.5% Pd) catalyst, the kinetics of their selective hydrogenation and the adsorption of their components have been studied.

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- . C₅, C₁₅, C₂₀ Pd/Al₂O₃ (0,5% Pd), .

     

Interaction of atomic fluorine with XeF2 and Xe at 77 K

The probabilities of the decay of atomic fluorine on solid xenon and xenon difluoride at 77 K have been determined.

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77 .

     

IR-spectroscopic studies of the interaction of pyridine bases with vanadium and molybdenum oxides supported on magnesia

As shown by IR-spectroscopic studies, pyridine bases interacting with V₂O₅ and MoO₃ supported on MgO form hydrogen bonds with surface hydroxyls and coordinate bonds with V and Mo ions. The interaction of 2,6-dimethylpyridine adsorbed on the surface with oxygen leads to the formation of 6-methylpyridine-2-carboxaldehyde, whose formyl group interacts with surface hydroxyls.

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, V₂O₅ MoO₃, MgO, V Mo. 2,6- 6--2-, OH-.

     

Proof of the kinetic reaction mechanism of PVC degradation using TA

The possibility of describing the kinetics of thermal degradation of PVC samples under both isothermal and nonisothermal conditions with a unique model and using the same set of parameters was investigated. Analysis of the experimental data revealed good agreement at higher temperatures (above 175 °C) when the catalytic action of generated HCl and its distribution in the sample were considered. At lower reaction temperatures, further experimental conditions and/or sample characteristics must be considered, and a modification of the model is necessary.

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Zusammenfassung Es wird die Möglichkeit untersucht, die Kinetik des thermischen Abbaus von PVC sowohl unter isothermen wie unter nichtisothermen Bedingungen durch ein einziges Modell und unter Verwendung des gleichen Parametersatzes zu beschreiben. Die Analyse der Messdaten zeigt gute Übereinstimmung bei hohen Temperaturen (über 175 °C), wenn die katalytische Aktivität des entwickelten HCL und seine Verteilung in der Probe berücksichtigt werden. Bei tieferen Temperaturen müssen weitere experimentelle Bedingungen und/oder Probeneigenschaften berücksichtigt werden, was eine Modifizierung des Modells erforderlich macht.

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. ( 175°), . , .

     

Influence of substituents on hydrogenation of nitro groups in aromatic hydrocarbons catalyzed by rhenium thiocomplexes

Homogeneous hydrogenation studies of (NO₂)_1–2–C₆H_3–4–L nitro compounds (where L=–H,–NH₂,–COOH,–CHO,–OH,–CH₃ and –CH=CH–COOH) catalyzed by Re₂S₆TThio₃Cl₂ in dimethylformamide solutions at and T=343 K, have revealed that the reaction is enhanced by electron-acceptor substitutents and hindered by electron-donor ones.

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(NO₂)_1–2–C₆H_3–4–L, L=–H,–NH₂,–COOH,–CHO,–OH,–CH₃,–CH=CH–COOH, Re₂S₆Thio₃Cl₂ 343 . , .

     

Gas phase hydrogenation of m-xylene on palladium catalysts

Gas phase hydrogenation of m-xylene on palladium supported catalysts was studied and compared with the hydrogenation of o-xylene. The modification in the stereoselectivity of palladium due to an increase in the acidity of the support is explained in terms of an increased residence time of the reactive species on the active surface, leading to a product composition closer to that predicted by thermodynamics.

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- -. , , .

     

Experimental setup to study catalysts by combined pulse microcatalytic and ESR spectroscopic methods

A setup consisting of an ESR spectrometer and a pulse microcatalytic installation is suggested for simultaneous kinetic and spectral measurements directly in catalytic processes.

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- , , .

     

Qualitative quantum-chemical models for surface OH groups of oxides

The dependence of the acidity and frequency characteristics of surface OH groups on the number and electronegativity of their bonded nonoxygen atoms has been analyzed in terms of the Del Re localized molecule orbitals method. The model suggested is applied, in particular, to interpret the nonmonotonous dependence of the stretching vibration frequencies for single-coordinated OH groups on the electronegativity of nonacid atoms for a great variety of oxides.

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Pe OH- . , , OH- .

     

A new method to obtain supported oriented oxides: MoO3 graphite catalyst in propylene oxidation to acrolein

Oriented MoO₃-graphite catalysts were prepared by oxyhydrolysis of a MoCl₅-graphite intercalation compound and used in catalytic oxidation of propylene. Results show a correlation between the building of specific crystal faces of MoO₃ and a selectivity towards acrolein formation.

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MoO₃- -MoCl₅- - . MoO, - .

     

Oxidative coupling of 5-membered heterocyclic compounds catalyzed by palladium(II)

Coupled heterocycles (bithiophenes, bifurans, furyl thiophenes) have been obtained in high yields via the reaction of thiophene and furan with palladium salts in solution at 50–100°C.

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50–100° (, , ) .

     

Formation and creeping of the crystalline phase wavefront within the bed of vanadium sulfuric acid catalyst

Kinetics of the reduction of sulfur dioxide by methane in the presence of molecular oxygen at 732–831°C have been obtained.

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732–831°C.

     

Quantitative thermal analysis,II

Some problems on adjustment of the equipment and on data evaluation, in view of the equations derived earlier for the calculation of specific heat and heat of transformation are discussed. It is shown that quantitative determinations are possible also if the adjustment is non-ideal and that both air and an inert material, respectively, may be used as reference material.

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Zusammenfassung Gewisse Probleme des Adjustierens der Ausrüstung und der Auswertung der Daten in Hinsicht auf die früher abgeleiteten Gleichungen zur Errechnung der spezifischen und Umwandlungswärmen wurden besprochen. Man bewies, daß quantitative Bestimmungen auch bei nichtidealem Adjustieren möglich sind bzw. daß Luft und Inertstoff gleichwie als Referenzstoffe dienen können.

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Résumé On discuté divers problèmes relatifs à la mise au point de l'appareillage et à l'évaluation des données, dans l'optique des équations déduites précédemment pour le calcul de la chaleur spécifique et de la chaleur de transformation. On montre qu'il est possible de faire des déterminations quantitatives même si la mise au point n'est pas idéale et que l'on peut utiliser comme substances de référence l'air aussi bien qu'un corps inerte.

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, . ë ë . , , « » , .

     

Influence of the pH of the preparation medium on surface properties of magnesium fluoride

The acidity and activity of MgF₂ in cyclohexene reactions wre studied as a function of the pH of MgF₂ preparation. Only samples prepared at pH 1.5 are acidic and catalytically active. It is proposed that the acidity of the MgF₂ surface is connected with the presence of sulfuric acid.

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pH MgF₂. pH 1,5 . , MgF₂ .

     

Michael addition of nitromethane to 3-buten-2-one catalyzed by potassium fluoride supported on Al2O3, ZnO, SnO2, sepiolite, AlPO4, AlPO4?Al2O3 and AlPO4?ZnO

The Michael addition of nitromethane to 3-buten-2-one has been carried out in the absence of solvent, using potassium fluoride supported on Al₂O₃, ZnO, SnO₂, sepiolite, AlPO₄, AlPO₄–Al₂O₃ and AlPO₄–ZnO catalysts. We found that KF/ZnO easily performed the Michael addition and thus, ZnO is a better support for the basic reagent than Al₂O₃. Besides, the Michael addition was not successful with AlPO₄ or AlPO₄-metal oxide acidic supports.

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3--2- , , Al₂O₃, ZnO, SnO₂, , AlPO₄, AlPO₄–Al₂O₃ AlPO₄–ZnO. , KF/ZnO .. ZnO, , , Al₂O₃. , , AlPO₄ AlPO₄- .

     

Kinetics of edta catalyzed oxidation of I? by Cr(VI)

The activity of various iron-containing ore catalysts during hydrogenation of Kansk-Achinsk lignite into liquid products in H-donor solvent (tetraline) has been studied. Ore samples contained pyrite, hematite and magnetite minerals. The most active appear to be pyrite samples. The catalytic effect of ore systems is, apparently, associated with the fact that during hydrogenation more active than tetraline H-donors are formed due to the hydrogenation of polycyclic aromatic molecules produced by thermal destruction of lignite.

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- H- . , , . , . , , , , , .

     

Thermal decomposition of crystalline molecular sieve (C3H7)3N-AlPO4-5

The thermal decomposition of (C₃H₇)₃N-AlPO₄-5 in inert and oxidizing gas atmospheres has been studied by TG, DTG and DTA in the temperature range 303–1273 K. The removal of tripropylamine occluded in the channels of the aluminophosphate occurs in a number of steps and is strongly influenced by the gas atmosphere.

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Zusammenfassung Die thermische Zersetzung von (C₃H₇)₃N-AlPO₄-5 wurde in inerter und oxydierender Gasatmosphäre mittels TG, DTG und DTA im Temperaturbereich von 303–1273 K untersucht. Der Austritt des in den Kanälen des Aluminiumphosphats okkludierten Tripropylamins erfolgt über eine Anzahl von Stufen und wird stark von der Gasatmosphäre beeinflußt.

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, (C₃H₇)₃N-AlPO₄-5 303–1273 . , , .

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We are grateful to Dr. V. G. Gunjikar, Mr. J. S. Gujaral and Dr. (Mrs) A. Mitra of the Special Instrument Group of our Laboratory for their co-operation in the work.     

Cobalt(III) dicarboxylato bis-ethylenediamine nitrates: Preparation and characterization by thermal analysis and other analytical methods

Compounds with the general formulacis ortrans-[Coen ₂ (RCOO)₂]NO₃ were prepared by modifications of known procedures; R was H, CH₃, C₂H₅ or C₃H₇, anden was ethylenediamine. The compounds were characterized by TLC and UV-Vis spectrophotometry, and their thermal behaviour was examined via TG and DTA, and via IR spectra on heated samples.The thermal stabilities are discussed in terms of the strengths of the bonds in the solids [1] and steric hindrance; the thermal decompositions are described with the aid of hypothesized intermediates and IR spectra.Reaction steps are identified and the thermal stability sequence is discussed: thecis compounds are less stable than the correspondingtrans compounds, due to the lower reticulation effect; the sequence of thecis compounds is the reverse of the sequence of carboxylate ion basicity, while the sequence displalyed by thetrans compounds can be interpreted in terms of solid lattice stabilization.

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Zusammenfassung Unter Durchführung einiger Abänderungen des bekannten Verfahrens wurden Verbindungen der allgemeinen Formel conf-Co[en₂(RCOO)₂]NO₃ hergestellt. Der AlkylrestR war H, CH₃, C₂H₅, C₃H₇ unden war Ethylendiamin. Die Verbidungen mitconf=cis odertrans wurden mittels TLC und UV-Spektrophotometrie charakterisiert. Ihr thermisches Verhalten wurdeanhand von TG, DTA und IR-Spektren von erhitzten Proben untersucht. Die thermische Stabilität wurde untersucht und in Abhängigkeit von Bindungsstärke und sterischer Behinderung diskutirt; weiterhin wurden die thermischen Zersetzungen mit Hilfe angenommener Intermediäre und deren IR-Spektren beschrieben. Die Reaktionsschritte wurden identifiziert und eine Stabilitätsreihe aufgestellt und diskutiert: cis-Verbindungen erwiesen sich als instabiler als die entsprechenden trans-Verbindungen, was einem geringeren Vernetzungseffekt zuzuschreiben ist; Die Reihenfolge folgt im Falle voncis dem Reziproken der Carboxylationenbasizität, während die Reihenfolge im Falle vontrans mittels der Gitterstabilisierung erklärt werden kann.

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, -[Coen₂(RCOO)₂]NO₃, R=H, CH₃, C₂H₅, C₃H₇, aen= . - - - . , . . , . : - , , . - -, - .

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This work was carried out with the financial support of the Consiglio Nazionale delle Ricerche (C.N.R.), which also gave a grant to one of us (A.M.G.).     

Oxidation of aroyl hydrazines, III. Kinetics and mechanism of the oxidation of nicotinoyl and isonicotinoyl hydrazine by iodine

The title reaction was studied in aqueous hydrochloric acid at high iodide concentations. The reaction is first order with respect to both oxidant and substrate though diisonicotinoyl hydrazines are the products apart from nitrogen. The reaction is markedly inhibited by H⁺ and I^– ions. An I^– ion independent path is also noticed.

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. , , -() , . H⁺ I^–. , , I^–.

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Part II: Indian J. Chem. (In press)     

Influence of ruthenium dispersity on its adsorption and catalytic properties

Hydrogen adsorption and the activity of Ru black of various dispersity in hydrogenation reactions have been investigated using a variety of methods. Decreasing dispersity decreases the heat of hydrogen adsorption, the activity and selectivity of the catalyst in the hydrogenation of various organic compounds.

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Ru- . , , .