Oxidative coupling of 5-membered heterocycles catalyzed by a Pd(II)-heteropolyacid system in dimethylformamide

Oxidative coupling of thiophene and 2-methylfuran to the corresponding dihetaryls in DMFA medium occurs in the presence of the homogeneous catalytic system Pd(II)-molybdovanodophosphoric heteropolyacid (HPA). The data obtained show that HPA may act as a reversible oxidant in polar aprotic media.

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, Pd(II)- 2- . , .

     

Thermal behaviour of thallium(I) fatty acid salts,II

The electrical conductivity (EC) changes of thallium(I) salts of fatty acids, which possess liquid crystalline phases, were investigated as a function of temperature. It was found that sharp EC jumps are associated with the phase transitions. The EC of the liquid crystalline phases depended not only on the temperature, the molecular weight and the geometry of the measuring cell, but also very sensitively on the heat treatment conditions which affect the relative magnitude of the EC in the mesophases.Study of these dependences revealed a memory effect. An explanation is given for this phenomenon.

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Zusammenfassung Die Änderungen der elektrischen Leitfähigkeit (EC) von Fettsäure-Thalium(I)-Salzen mit flüssig-kristallinen Phasen wurden als Funktion der Temperatur untersucht. Es wurde festgestellt, daß den Phasenübergängen scharfe EC-Sprünge entsprechen. Die EC der flüssig-kristallinen Phase hängt nicht nur von der Temperatur, dem Molekulargewicht und der Geometrie der Meßzelle ab, sondern auch — in sehr empfindlicher Weise — Phasen bestimmen.Die Untersuchung dieser Zusammenhänge führte zur Beobachtung eines »Memorieeffektes« Eine Erklärung dieser Erscheinung wird gegeben.

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Résumé On a étudié les variations de la conductibilité électrique (EC) des sels de thallium(I) des acides gras possédant des phases cristallines liquides, en fonction de la température. On a établi que les variations brusques d'EC correspondent aux transitions de phases. L'EC des phases cristallines liquides dépend non seulement de la température, de la masse molaire et de la géométrie de la cellule de mesure, mais aussi, et d'une manière très sensible, des conditions du traitement thermique qui affectent l'amplitude relative de l'EC dans les mésophases.Un «effet de mémoire» a été observé lors de l'étude de ces phénomènes, dont on donne une explication.

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(I) , , . , . - , , , . « ». .

     

Preparation and characterization of Ru?Pb supported catalysts

Decomposition of Mn₃Mo₂TeO₁₂ during oxidation of toluene to benzaldehyde was observed. Depending on the surface composition of the initial catalyst, the decomposition leads to less active but highly selective MnMoTeO₆ or to MnMoO₄ which is not selective in toluene oxidation.

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Mn₃Mo₂TeO₁₂ . , MnMoTeO₆, MnMoO₆.

     

Photoinduced oxygen adsorption of AgBr crystals at 77 K

Photoinduced adsorption (PIA) of oxygen molecules on AgBr films at 77 K has been experimentally observed and investigated. Lifetimes of PIA centers and desorption activation energies of O₂ molecules have been determined. The process is suggested to compete with the ionic step of AgBr photolysis.

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- () - AgBr 77 K. - O₂. , , - AgBr.

     

Polyfunctional zeolite catalysts in the benzene-olefin-hydrogen system

Benzene alkylation by C₂–C₄ olefins in the presence of hydrogen over a steam-treated zeolite catalyst containing lanthanum and nickel, has been studied. The promoting action of hydrogen on benzene alkylation by propylene has been established.

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C₂–C₄ , . .

     

Autocatalysis in the formose reaction

It has been found that carbohydrates naturally present in ppm quantities in paraformaldehyde are the cause of the autocatalysis in the formose reaction of paraformaldehyde solutions. Paraformaldehyde sublimed into Ca(OH)₂ suspension was not transformed to sugars by formose reaction, only to methanol and formate by Cannizzaro reaction. A minute trace of glycolaldehyde — 3 ppm — was sufficient to initiate conventional autocatalysis. A formose reaction scheme in which formaldehyde reacts only with sugars by aldol condensation but not with itself is proposed.

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, , .. . , Ca(OH)₂, , , . — 3 .. — . , , .

     

Temperature-programmed desorption (TPD) of various bases from HY zeolites

The temperature programmed desorption of several bases from a HY zeolite has shown that the activation energy of desorption represents a useful measure for characterizing the acidic properties.

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- HY , , .

     

Calculation of thermal effects in DTA

By considering that the temperature of the end of the thermal effect and the return of the thermal curve to the baseline do not coincide new calculation methods for the thermal effect become possible. Both the integral value of the thermal effect and its distribution over temperature may be calculated by processing only that part of the DTA curve which corresponds to the temperature interval of the transformation.It is demonstrated on the examples of non-variant transformation and transformation with an even distribution of the thermal effect over the temperature interval of the transformation that, under certain assumptions, the values of the thermal effect calculated by the suggested method and by the area of the peak are identical.

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Zusammenfassung Bei Berücksichtigung, daß die Temperatur des Endes des thermischen Effekts und die Rückkehr der thermischen Kurve zur Grundlinie nicht zusammenfallen, werden neue Methoden zur Berechnung des thermischen erschlossen. Sowohl der Integralwert des thermischen Effekts, als auch seine Verteilung in dem Temperaturbereich können durch Behandlung ausschließlich desjenigen Teils der DTA-Kurve berechnet werden, welcher dem Temperaturbereich der Umwandlung entspricht.Anhand von Beispielen der nicht-varianten Transformation und der Transformation mit gleichmäßiger Verteilung des thermischen Effekts im Temperaturbereich der Umwandlung wurde gezeigt, daß — unter gewissen Voraussetzungen — die Werte des durch die vorgeschlagene Methode und des aus der Peakfläche berechneten thermischen Effekts identisch sind.

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Résumé En considérant le fait que la température de la fin de l'effet thermique et le retour à la ligne de base de la courbe ATD ne coïncident pas, on a développé de nouvelles méthodes du calcul de l'effet thermique. La valeur intégrale de l'effet thermique ainsi que sa distribution dans l'intervalle de températures peuvent être calculées en ne considérant que la partie de la courbe ATD qui correspond à l'intervalle de température de la transformation.A l'aide d'exemples de transformations invariantes et de transformations à distribution uniforme de l'effet thermique dans l'intervalle de températures de la transformation, on a montré qu'avec certaines hypothèses, les valeurs de l'effet thermique calculées par la méthode proposée et à partir des surfaces des pics, sont identiques.

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. , -, . , , .

     

Oxidative elongation of lower paraffins

It is shown that the oxidative condensation of ethane on CoMo/-Al₂O₃ catalysts is in principle possible. The conceivable paths of this reaction are analyzed.

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- .

     

Combination and disproportionation of methyl and 2-propyl radicals with 1,1,2-trimethylallyl radicals

The combinations and disproportionations of the CH₃ and 2-propyl (iP) radicals with the 1,1,2-trimethylallyl (TMA) radical have been studied in the gas phase in the temperature interval of 389–451 K and 490–540 K, respectively. For the ratios of the terminal (t) and non-terminal (n) combinations of the CH₃ and iP radicals with the TMA radical, values of 1.9±0.1 and 2.84±±0.10 were obtained, respectively. The ratios of the tt and tn and nn to tn combinations of the TMA radical were 1.59 and 0.46, respectively. The disproportionation-combination rations were (CH₃ , TMA)=0.022±±0.012 and (iP, TMA)=0.026±0.011.

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CH ₃ 2- (iP) 1,1,2- (TMA) : 389–451 K 490–540 K. (t) (n) TMA 1,9±0,1 2,84±0,10, . tt tn nn tn TMA 1,59 0,46, . (CH ₃ , TMA)=0,022±0,012 (iP, TMA)=0,026±0,011.

     

IR investigation of phenol methylation on MgO

The adsorption of phenol, anisole, o-cresol and methanol on MgO was studied by infrared spectroscopy. The surface species of phenol, anisole and o-cresol were of the phenolate type and for methanol of the methoxide type.

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, , - MgO . , - , — .

     

Kinetics of carbonyl triplet reactions in water

The presence of urea during the gelling of AlPO₄–Al₂O₃ catalysts (AlPO₄/Al₂O₃ weight ratio =3) has been studied with respect to its effect on the porous texture and surface acidity of the resulting gels. An increase in pore volume and mean pore radius with no modification in surface acidity is found when the AlPO₄–Al₂O₃ catalyst is modified by the addition of 5 mol% urea in the AlPO₄ solution.

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, AlPO₄/Al₂O₃ ( AlPO₄/Al₂O₃=3) . , AlPO₄/Al₂O₃ 5 .% AlPO₄ - .

     

Etude thermoanalytique de quelques steroides I — Monovalerianate d'estradiol et estriol

A thermoanalytical study of estradiol monovalerate (a) and estriol (b) revealed the thermal stability, the decomposition kinetics, and the temperatures and intervals of fusion. The degree of purity was calculated only for estradiol monovalerate: 99.72 ± 0.11 mol %. The fusion enthalpy (29.45±0.47 kJ mol^–1) and entropy for this compound were evaluated by differential scanning calorimetry. It was also possible to detect the polymorphism and the pseudopolymorphism of (a) and (b) after recrystallization from several solvents.

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Zusammenfassung Die thermische Stabilität, die Zersetzungskinetik sowie die Schmeiztemperaturen und -intervalle von Estradiol-Monovalerianat (a) und Estriol (b) wurden thermoanalytisch ermittelt. Nur der Reinheitsgrad von (a) wurde berechnet (99,72 ± 0,11 mol %). Die Schmelzenthalpie (29,45±0,47 kJ · mol^–1) und Schmelzentropie dieser Verbindung wurden mittels DSC bestimmt. Nach Rekristallisation in verschiedenen Lösungsmitteln konnten Polymorphie und Pseudopolymorphie für (a) und (b) nachgewiesen werden.

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, . 99,72±0,11 %. (29,45±0,47 · ^–1) . , .

     

Effects of tempering time and tempering temperature of caustic mercerization on the spectral and electrical properties of Egyptian cotton fibres

Several samples of Egyptian cotton fabric strips were subjected to various caustic mercerization conditions, varying in temperature and time. On these samples extensive measurements were undertaken, comprising X-ray diffraction, IR absorption spectra and the temperature-dependence of DC-electric conductivity.The phase constitution, % crystallinity, IR band assignment, activation energies for conduction and energy gap were evaluated as a function of caustic mercerization. The results obtained were correlated and discussed in detail, leading to valuable information of use in the cotton fabric strip industries.

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Zusammenfassung Verschiedene Proben von ägyptischen Baumwollstreifen wurden unter verschiedenen Bedingungen (Temperatur, Zeit) einer Laugung unterworfen. Die gelaugten Proben wurden eingehend durch Röntgendiffraktometrie, IR-Absorptionsspektroskopie und Messungen der Temperaturabhängigkeit der elektrischen Gleichstromleitfähigkeit untersucht. Phasenstruktur, Kristallinität, Zuordnung der Banden, Aktivierungsenergien für die Leitfähigkeit und verbotene Bänder wurden in Abhängigkeit von der Laugung ermittelt. Die erhaltenen Ergebnisse wurden miteinander verglichen und in Einzelheiten diskutiert, wobei für die Baumwollverarbeitungsindustrie wertvolle und empfehlenswerte Informationen erhalten wurden.

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. , . , , , . , .

     

Recombination mechanism of hydrogen atoms on ZnS surface

It has been established that physically adsorbed and chemisorbed atoms take part in the recombination of H-atoms on ZnS surface.

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- ZnS .

     

Coke deposition on naphtha reforming catalysts: I. Influence of the hydrocarbon feed

During hydrocarbons reactions over Pt/Al₂O₃ the catalyst is covered by coke. It is accepted that coke formation occurs on metal and acid sites. During normal heptane and methylcyclopentane reforming it was found that the nature and the rate of coke deposited on the catalyst surface was not same, depending on the structure of the hydrocarbon feed.

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Pt/Al₂O₃ . , . , - .

     

Evaluation of quantum yields in the presence of an absorbing additive

A method is proposed for the evaluation of quantum yields of photochemical reactions studied in the presence of absorbing additives using cylindrical sample tubes.

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.

     

Kinetics of CO2 formation in thermal destruction of brown coals

The previously suggested approach to the problem of kinetic system identification /1/ was used for the system of independent first order reactions. The analysis of the curves of CO₂ formation in thermal destruction of brown coal indicates that both structure and model parameters of real processs can be identified in terms of the continuity concepts.

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(I) ë . CO₂ , , .

     

Physico-chemical transformations during heating of phosphorites

The thermal behaviour of phosphorites in an oxygen or helium atmosphere was studied by means of simultaneous TG-DTG-DTA-gas titrimetric EGA. Thermal oxidation and/or decomposition steps of the contaminating organic materials, carbonate minerals and pyrite, and of the fluorocarbonate-apatite were identified. The evolution of CO₂ from the latter has its maximum at 750–850 °C and is accompanied by an increase in the lattice parametera ₀.

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Zusammenfassung Das thermische Verhalten von Phosphoriten in Sauerstoff- oder Heliumatmosphäre wurde durch simultane TG-DTG-DTA-EGA (mittels Gastitrimetrie) untersucht. Thermische Oxidations- und/oder Zersetzungsschritte der Verunreinigungen (organische Materialien, Carbonatminerale und Pyrit) und des Calcium-fluoro-carbonat-apatit wurden identifziert. Die CO₂-Abspaltung aus dem letzteren hat ihr Maximum bei 750–850 °C, sie ist begleitet von einer Vergrösserung des Gitterparametersa ₀.

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, , - . ( , , . 750–850° ₀.

     

Correlation between oxygen binding energy and catalytic activity of oxides

Oxygen binding energy is suggested as a measure for the ability of oxide cations to enter into weak chemical interactions with reactant molecules, which is a necessary prorequisite for the adsorbability and catalytic activity of oxides.

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, . .