Oxidative coupling of thiophene catalyzed by Pd(II)

The yield and isomer composition of bithiophene in the oxidative coupling of thiophene catalyzed by Pd(II) in the presence of Fe(III) salts have been studied. The reaction mechanism is discussed.

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, Pd(II) Fe(III). .

     

Thermal desorption of atmospheric organic pollutants enriched on charcoal

A technique of thermal vacuum desorption of charcoal, used in passive dosimeters to enrich organic pollutants of toxicological importance, is described. It combines the advantages of the classic procedure of using highly active charcoal followed by solvent desorption and the environmental one-step procedure of analyzing the whole thermally desorbed sample. For pollutants such as trichloroethylene, tetrachloroethylene, ether, benzene and ethanol, the recovery and reproducibility are satisfactory. The unexpected decomposition of halothane and ethylacetate at higher temperatures is caused by the catalytic activity of the charcoal, but this can be tolerated under constant operating conditions.

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Zusammenfassung Eine Methode zum Anreichem toxikologisch bedeutender organischer Luftverunreinigungen durch thermische Vakuumdesorption von Aktivkohle nach dem Einsatz in passiven Dosimetern wird beschrieben. Die Methode kombiniert die Vorteile der klassischen Prozedur unter Verwendung hochaktiver Kohle mit nachfolgender Desorption durch Lösungsmittel einerseits mit denen der Umwelt-Analyse der gesamten desorbierten Probe in einem Schritt andererseits. Für Luftverunreinigungen wie Trichlorethylen, Tetrachlorethylen, Ether, Benzen und Ethanol werden ausreichende Wiedergewinnung und Reproduzierbarkeit ermittelt. Die unerwartete Zersetzung von Halothan und Ethylacetat bei höheren Temperaturen wird auf die katalytische Wirkung der Aktivkohle zurückgeführt. Sie kann unter konstanten Versuchsbedingungen jedoch toleriert werden.

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, . . , - , , . .

     

XPS, UPS and TDS studies of CO adsorption on platinum

XPS, UPS and TDS studies of the adsorption of carbon monoxide on partially recrystallized platinum foil at 300 K indicate that the adsorption is of nondissociative character and there are two CO_ads states.

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300 K. , . CO.

     

Thermal analysis in studies of photochemical transformations in PVC

The effects of photochemical processes in PVC in response to UV irradiation at 253.7 nm on its thermal stability were investigated. It was found that small differences in the efficiency of the photochemical processes taking place in the PVC can be recorded in the thermal measurements, and that photodehydrochlorination lowers the temperature of thermal dehydrochlorination, while photooxidation and crosslinking increase the temperature of complete decomposition of this polymer.

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Zusammenfassung Der Einfluß der durch UV-Bestrahlung bei 253,7 nm hervorgerufenen fotochemischen Prozesse auf die thermische Stabilität von PVC wurde untersucht. Mittels der thermischen Untersuchungen wurde gefunden, daß im Ergebnis der im PVC stattfindenden fotochemischen Prozesse kleine Unterschiede bestehen. Fotodehydrochlorierung vermindert die Temperatur für die thermische Dehydrochlorierung, während Fotooxidation und Vernetzung die Temperatur für die vollständige Zersetzung dieses Polymers erhöhen.

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() , 253,7 . , , , . , , .

     

Dispersity of (Ru+Pd)/SiO2 catalysts and their properties in CO hydrogenation and ethane hydrogenolysis

The decreased activity of bimetallic catalysts obtained by the interaction of Ru₃(CO)₁₂ with Pd/SiO₂ in the synthesis of hydrocarbons from CO and H₂ and in ethane hydrogenolysis compared with Ru/SiO₂ is due to the dilution, of ruthenium by less active palladium atoms.

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, Ru₃(CO)₁₂ Pd/SiO₂, CO Ru/SiO₂ .

     

Comportement thermique des benzènesulfonates de lithium,sodium et potassium

Résumé Le comportement thermique des benzènesulfonates de lithium, sodium et potassium a été étudié par TG et ATD à l'air et sous atmosphère d'azote.Dans la zone de stabilité des sels anhydres, nous avons mis en évidence des transformations réversibles (changements de phase cristalline) dont certaines ont fait l'objet de mesures calorimétriques.L'étude des résidus solides de la décomposition a montré une proportion importante de sulfates dans les produits obtenus dans l'air, alors que sous azote, il s'agissait surtout de sulfures. Les sulfites ne se présentent qu'en très faible quantité dans les deux cas.

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The thermal behaviour of benzènesulphonates of lithium, sodium and potassium has been investigated by TG and DTA in air and in an atmosphere of nitrogen.We have shown in the stability interval of the anhydrous salts reversible transformations (phase transitions), some of which were quantitatively studied by calorimetry.The radiocristallographic study of the solid residues has shown an important proportion of sulphates in the residues in air and of sulphides in an inert atmosphere. The sulphites were found in very small quantity in both cases.

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Zusammenfassung Das thermische Verhalten der Benzolsulfonate von Lithium, Natrium und Kalium wurde durch TG und DTA in Luft und in Stickstoff untersucht.Im Stabilitätsbereich der wasserfreien Salze wurden reversible Umwandlungen (Phasenübergänge) nachgewiesen, von denen einige quantitativ durch Kalorimetrie untersucht wurden.Das radiokristallographische Studium der festen Rückstände zeigte, daß in Luft ein bedeutender Anteil der Rückstände aus Sulfaten und in inerter Atmosphäre aus Sulfiden besteht. Sulfite wurden in beiden Fällen in sehr geringen Mengen gefunden.

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

     

Epoxidation of cyclohexene with tert-butyl hydroperoxide catalyzed by polymer anchored molybdenum complexes

Catalytic activity of molybdenum hexacarbonyl anchored on various polymers was investigated for the epoxidation of cyclohexene with tert-butyl hydroperoxide. The activity was increased by anchoring on the polymer. The catalyst on polystyrene showed much higher activity than Mo(CO)₆ used under homogeneous conditions.

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, , .— . . ]qt, Mo(CO)₆, .

     

Formation and thermal decomposition of silicon oxynitride compounds. Part III

The formation of a previously unknown compound with stoichiometry Li₆SiN₂O₂ was found during studies on the reactivity of Li₂SiN₂ with Li₂O, of SiO₂ with Li₃N and of Li₃SiNO₂ with Li₃N.

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Zusammenfassung Die Bildung einer bisher unbekannten Verbindung der Stöchiometrie Li₆SiN₂O₂ wurde bei Untersuchungen der Reaktivität von Li₂SiN₂ mit LiO, von SiO₂ mit Li₃N und von Li₃SiNO₂ mit Li₃N beobachtet.

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Li₆SiN₂O₂ Li₂SiN₂ , , Li₃SiNO₂ .

     

Difference method of evaluation of dynamic integral thermogravimetric curves in decomposition of polypropylene

A new differential method of evaluating integral thermogravimetric records of the formation of volatile products during the degradation of polypropylene in air is presented. The method, applied to 0–100% conversion of the polymer to volatile products, may distinguish the initial presence of low molecular compounds in the polymer, as well as changes in the mechanism of degradation of the material.

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Zusammenfassung Es wird eine neue differentielle Methode zur Auswertung der die Bildung von flüchtigen Produkten während der Zersetzung von Polypropylen in Luft widerspiegelnden integralen thermogravimetrischen Kurven dargelegt. Mit der im Bereich 0–100% Konversion von Polymer zu flüchtigen Produkten anwendbaren Methode können sowohl die Anwesenheit niedermolekularer Verbindungen im Polymer als auch Veränderungen im Abbaumechanismus des Materials erkannt werden.

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, . , 0–100%- , , .

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

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pH=8+9. .

     

Studies of the structure of multicomponent Raney nickel catalysts

Genesis and structure of Raney nickel catalysts modified by Mo, Fe and Ca have been studied by XPS, SIMS and Auger and electron microprobe methods. It has been established that these catalysts are inhomogeneous and their structure can be described by models accounting for the interaction and localization character of metal components, their oxides and hydroxides.

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, - Ni-, Mo, Fe Ca. , , , .

     

Reactivity of hydrogen adsorbed on platinum black towards ethylene

TPD studies of the reactivity of hydrogen adsorbed on dispersed Pt-black towards ethylene at –90, 30 and 200°C indicate that molecular forms of hydrogen with E_des from 3 to 16 kcal/mol are reactive species.

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Pt- –90, 30, 200°C . , . 3 16 /.

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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, H⁺. . , , , .

     

Structure and interconversion of intermediates in pyridine-catalyzed mesylation reactions

The structure of intermediates of pyridine-catalyzed mesylation processes, i.e. sulfene and sulfonyl salts, and the ways of their interconversion have been studied by the joint use of semi-empirical MNDO approximation and methods of molecular mechanics. Calculation results agree well with the kinetic data.

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, : , . .

     

The activity of Ni/AlPO4, Ni/AlPO4?Al2O3 and Ni/AlPO4?SiO2 catalysts in the hydrogenation of e-cinnamaldehyde

Liquid-phase catalytic hydrogenatio of E-cinnamaldehyde was carried out by using new supported nickel catalysts (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ and Ni/AlPO₄–SiO₂) in methanol as solvent under low hydrogen pressure (4.1 bar) and 298 K. The kinetic orders are zero in H₂ and aldehyde. The selectivity to the hydrogenaton of the C=C double bond is very high (>99%)

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- (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ Ni/AlPO₄–SiO₂) (4,1 ) 298 . H₂ . C–C (>90%).

     

TPD studies of hydrogen adsorption on group VIII metals

Hydrogen desorption proceeds in several temperature regions and differs by its order of magnitude and activation energy. Differential curves of adsorbed hydrogen distribution with respect to the desorption activation energy, dN/dE (E), show a considerable inhomogeneity of adsorbed atomic species and the energetic homogeneity of molecular species.

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. dN/dE (E) .

     

A new method of DTA: Theory and practice

A novel differential thermoanalytical technique is described and discussed with regard to function, operation, performance, theory and application. Information is provided about the nature of the internal processes taking place at the time of absorption or release of energy. Notable features of the technique include high sensitivity and independence of a reference sample.

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Zusammenfassung Eine neue differentialthermoanalytische Technik wird hinsichtlich ihrer Funktion, Arbeitsweise, Leistung, Theorie und Anwendung beschrieben. Es wird über die Beschaffenheit der inneren Vorgänge bei der Energie-Absorption oder -Freisetzung berichtet. Vorteile der neuen Technik sind die hohe Empfindlichkeit und die Unabhängigkeit von der Referenzprobe.

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Résumé On décrit et discute une nouvelle technique d'ATD en considérant sa fonction, son utilisation, ses possibilités, sa théorie et son application. On indique les processus internes qui se produisent lors de l'absorption ou de la libération d'énergie. Les principales caractéristiques de la technique se rapportent à la sensibilité élevée et à l'indépendance de l'échantillon de référence.

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, , , , , . .

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We wish to acknowledge support of this research by the National Research Council of Canada and Dalhousie University, Halifax.     

Kinetic study of the thermal decomposition of heterocyclic thiol complexes under non-isothermal conditions

The thermal decomposition in the solid-phase has been studied by thermogravimetric (TG) and differential thermal analysis (DTA) techniques for a number of heterocyclic thiol complexes. The method of Coats and Redfern was used to study the kinetics of the thermal decomposition process. The enthalpy changes and activation energies for the decomposition have been calculated.

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Zusammenfassung Die thermische Zersetzung in fester Phase wurde an einigen heterozyklischen Thiolkomplexen mit den Methoden der dynamischen Thermogravimetrie (TG) und der Differentialthermoanalyse (DTA) untersucht. Die Methode von Coats und Redfern wurde zum Studium der Kinetik des thermischen Zersetzungsvorganges eingesetzt. Die Enthalpie-Änderungen und Aktivierungsenergien der Zersetzung wurden berechnet.

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Résumé Etude de la décomposition thermique en phase solide de plusieurs complexes thiols hétérocycliques par thermogravimétrie (TG) et par analyse thermique différentielle (ATD). La méthode de Coats et Redfern a été appliquée pour déterminer la cinétique du processus de la décomposition thermique. Les variations d'enthalpie et les énergies d'activation de la décomposition ont été calculées.

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(TG) (DTA) . . .

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We are grateful to Prof. K. C. Joshi, Head of the Chemistry Department and Dr. A. K. Rai of Rajasthan University, Jaipur for permitting the generous use of the thermorecording balance at the University and to Dr. E. R. Saxena, Assistant Director, Mineral Products and Inorganic Chemicals Division and Mr. P. Narayanachar of Regional Research Laboratory, Hyderabad for their valuable assistance in taking DTA trace. Thanks are also due to Prof. V. V. S. Murti, Head of the Chemistry Department, University of Delhi for his interest in the work. The author (K. A. V.) thanks the University Grants Commission, New Delhi for the award of the fellowship under which these investigations have been carried out.     

Investigation of the self-heating phenomenon in the bulk polymerization of acrylonitrile

The temperature of the polymerizing system was measured with a thermistor during the bulk polymerization of acrylonitrile initiated by azoisobutyronitrile. The temperature of self-heating suddenly rises at a conversion of about 2%. This jump of temperature is presumably caused by the formation of a gel structure and, consequently, the outfall of thermal convection within the system.

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, -- . , - . - , .