Thermochemical studies on the systems ACl/CeCl3 (A=Na-Cs)

The pseudobinary systems ACl/CeCl₃ (A=Na-Cs) were reinvestigated by means of DTA. The following compounds were found and identified through their X-ray patterns (primarily detected compounds in italics):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅,CsCe ₂ Cl ₇. The compounds A₂CeCl₅ crystallize with the K₂PrCl₅ structure. The high-temperature modifications of the compounds A₃CeCl₆ have the cubic elpasolite structure. The hexagonal unit cell of KCe_1.67Cl₆ is related to the CeCl₃ structure: 0.33 Ce³⁺ are substituted by one K^s+. The structure of CsCe₂Cl₇ can be described with a hexagonal subcellZ=4,a=9.72 andc=14.94 Å; however, small superstructure reflexions reduce the symmetry.The thermodynamic functions for the reactionsnACl+CeCl₃=A _n CeCl _n+3(A=K, Rb) were determined by means of e.m.f. measurements.Measurements of the e.m.f.E vs. T yielded the Gibbs enthalpiesG ^r . The temperature-dependence was found to be linear.The most important result is the formation of the elpasolites (A₃CeCl₆) and ACe₂Cl₇.

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Zusammenfassung Die pseudobinären Systeme ACl/CeCl₃ (A=Na-Cs) wurden mittels Differenzthermoanalyse (DTA) neu untersucht. Folgende Verbindungen wurden gefunden und durch ihre Röntgenbeugungsmuster charakterisiert (erstmalig nachgewiesene Verbindungen sind kursiv):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅,CsCe ₂ Cl ₇. Die Verbindungen A₂CeCl₅ kristallisieren im K₂PrCl₅-Typ. Die Hochtemperaturmodifikationen der Verbindungen A₃CeCl₆ liegen in der kubischen Elpasolith-Struktur vor. Die hexagonale Elementarzelle des KCe_1.67Cl₆ ist mit der CeCl₃-Struktur verwandt: 0,33 Ce³⁺ sind durch ein K⁺ ersetzt. Die Struktur des CsCe₂Cl₇ kann mit einer hexagonalen Pseudozelle beschrieben werden:a=9,72;c=14,94Å;Z=4; schwache Überstrukturreflexe reduzieren jedoch die Symmetrie. Die thermodynamischen Funktionen für die Reaktionen:n ACl + CeCl₃=A _n CeCl _n+3 (A=K, Rb) wurden durch EMK-Messungen bestimmt. Messungen der Abhängigkeit von e. m. f.E gegenT ergaben die Gibbs-EnthalpienG ^r . Es wurde eine lineare Temperaturabhängigkeit gefunden. Als wichtigstes Resultat ist die Bildung von Elpasoliten (A₃CeCl₆) und von Verbindungen (ACe₂Cl₇) anzusehen.

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ACl/CeCl₃, A . - ( ):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅ CsCe ₂Cl₇. A₂CeCl₅ K₂PrCl₅. A₃CeCl₆ . KCe_1.67Cl₆ CeCl₃, 0,33 Ce³⁺ . CsCe₂Cl₇ a=9,72 Å,c=14,94 Å Z=4. , . n ACl + CeCl₃=A _n CeCl _n+3(A=K, Rb) . . . . . .E , G ^r . ACe₂Cl₇.

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Presented as a poster at the 8th ICTA, Bratislava, 1985.

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Heat capacity of niobium chlorides in the range 6–320 K

The heat capacities of NbCl₅ and Nb₃Cl₈ samples with less than 1·10^–3 mass-% of impurities were determined over the range 6–320 K by an adiabatic calorimeter. An anomaly was found in Nb₃Cl₈ within the 7–13 K range. Comparisons ofC _p values of Nb₃Cl₈ are made with the theoretical works of Tarassov. The qualitative fit is quite good.

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Zusammenfassung Die Wärmekapazitäten von NbCl₅- und Nb₃Cl₈-Proben mit Verunreinigungsgehalten 10^–3 Masse-% wurden mit einem adiabatischen Kalorimeter bei 6 bis 320 K bestimmt. Am Nb₃Cl₈ wurde eine Anomalie bei 7 bis 13 K nachgewiesen. Die C_p-Werte von Nb₃Cl₈ werden mit theorischen Ergebnissen von Tarassov verglichen, die qualitative Übereinstimmung ist gut.

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6–320 NbCl₅ Nb₃Cl₈ , 1· 10^–3 . Nb₃Cl₃ 7–13 . _p Nb₃Cl₈ , .

     

Der Phasenübergang C-Typ-PrO1.50 → A-Typ-PrO1.50

Zusammenfassung Durch thermodilatometrische und DTA-Untersuchungen wurde das thermische Verhalten von C-Typ-PrO_1.50, A-Typ-PrO_1.50 und PrO_1.833 im Temperaturintervall von Raumtemperatur bis 1200 °C in Luft und Wasserstoff-Atmosphäre untersucht. Die Temperatur des Phasenüberganges C-PrO_1.50 A-PrO_1.50 wurde zu 790±10 °C gefunden. C-PrO_1.50 ist nur unterhalb der Umwandlungstemperatur beständig, A-PrO_1.50 im gesamten untersuchten Temperaturbereich. PrO_1.833 geht oberhalb von 400 °C, in Luft erhitzt, über mehrere definierte oxidische Zwischenphasen in A-PrO_1.50 über.

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The thermal behaviour of C-type PrO_1.50, A-type PrO_1.50 and PrO_1.833 was investigated by thermodilatometric and DTA measurements in the temperature range from 20 to 1200 °C in air and in a hydrogen atmosphere. The phase transition C-type PrO_1.50 A-type PrO_1.50 proceeds at 790±10 °C; C-type PrO_1.50 is stable only below this temperature, but A-type PrO_1.50 in the whole range. Pro_1.833 is stable up to 400 °C at atmospheric pressure. When heated further it decomposes stepwise forming several defined intermediate oxide phases.

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Résumé On a étudié par thermodilatométrie et ATD le comportement thermique de PrO_1.50-type C, PrO_1.50-type A, et PrO_1.833, dans le domaine de température allant jusqu'à 1200 °C, dans l'air et en atmosphère d'hydrogène. On a trouvé 790±10° comme température de la transition de phase C-PrO_1.50/A-PrO_1.50. C-PrO_1.50 n'est stable qu'au-dessous de la température de conversion, alors que A-PrO_1.50 l'est dans tout le domaine de température examiné. PrO_1.833 chauffé dans l'air se transforme au-dessus de 400 °C en donnant plusieurs phases intermédiaires d'oxydes définis avant A-PrO_1.50.

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PrO_1.50, PrO_1.50 PrO_1.833, 20–1200° . PrO_1.50 PrO_1.50 790±10°; PrO_1.50 ; PrO_1.50 PrO_1.833 400° . , , .

     

Thermal analysis in the study of the new oxide-based superconductors

Thermoanalytical methods offer a convenient means for testing the starting materials used in the synthesis of the ceramic superconductors and for establishing the reaction and annealing temperatures as well as the stoichiometry of the end product. In addition, the stability and other thermal properties of the superconducting materials can be investigated including phase transformations during thermal cycling and possible reactions with substrates and the environment. The applications of TG, DSC/DTA and other thermal techniques for the study of the YBa₂Cu₃O_7–x superconductor are briefly reviewed using results from own experiments and selected literature data to illustrate the examples given.

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Zusammenfassung Thermoanalytische Methoden eignen sich zum Erproben von Ausgangsmaterialien zur Synthese von Keramiksupraleitern und zur Ermittlung der Reaktions- und Glühtemperaturen sowie der stöchiometrischen Zusammensetzung der Endprodukte. Außerdem können die Stabilität und andere thermische Eigenschaften der supraleitenden Materialien, einschließlich deren Phasenübergängen beim Wärmecycling sowie möglicher Reaktionen mit Substraten oder mit der Umwelt untersucht werden. Es wird kurz die Anwendung von TG-, DSC/DTA- und anderen thermischen Verfahren bei der Untersuchung des Supraleiters YBa₂Cu₃O_7–x beschrieben sowie Ergebnisse aus eigenen Experimenten un zur Illustration der aufgeführten Beispiele ausgewählte Literaturangaben gegeben.

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, , , . , , . , / YBa₂Cu₃O_7–x, , .

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This work has been supported by the Technology Development Centre (TEKES) through grant 4126/1988. The stimulating discussions and cooperation with Professor T. Katila and his group as well as Mr. K. Härkönen, M.Sc. are gratefully acknowledged. Mr. I. Danielsson from Oy Philips Ab is thanked for the permission to publish the high-temperature XRD pattern.     

Unsteady-state performance of NOx catalytic reduction by NH3

Experimental results of studying NO_x catalytic reduction by NH₃ under periodic reversals in the direction of filtration of the mixture purified in a catalyst bed are discussed.

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NO_x .

     

Acid properties of ZSM-5 zeolites after hydrothermal treatment at 540°C

Acid properties of ZSM zeolites have been studied under various conditions of hydrothermal treatment. It is shown that with increasing , the concentration of proton centers monotonically decreases and variations in the concentration of Lewis acid centers is of extremal character.

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ZSM . , , .

     

Mechanism of proton transfer from 2-nitrohexafluoropropane to amines

According to the analysis of NMR kinetic data, the proton transfer from the CH-acid 2-nitrohexafluoropropane to trioctylamine occurs in a hydrogen-bonded complex. The value of the k_H/k_D ratio (6) and the linearity of the ln k vs. T^–1 dependence indicate a classical mechanism of the process.

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2- . . , . k_H/k_D 6 .

     

Decay of 1.643-hr 95Ru to 95Tc

The decay of ⁹⁵Ru has been investigated by means of -ray spectroscopy. The ⁹⁵Ru nuclei were produced by the reaction ⁹²Mo(,n)⁹⁵Ru at the beam energy of 17 MeV. High-purity Ge detectors have been used singly and in coincidence to study -rays in the decay of ⁹⁵Ru to ⁹⁵Tc. 132 -rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of ⁹⁵Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated logft values, measured -ray branching ratios, and in-beam experiment results of the daughter nucleus ⁹⁵Tc.     

Vinylation of 5-membered heterocycles by ethylene in the presence of palladium(II)

The reaction between ethylene and 5-membered heterocyclic compounds (thiophene, furan, furfural) in solution in the presence of a palladium salt at 25–100°C and atmospheric pressure is found to give good yields of 2-vinyl derivatives of the heterocycles indicated.

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5- (, , ) 25–100° 2- .

     

Catalytic oxidation of propylene to acrolein on a multicomponent oxide catalyst

Rate equations have been found and reaction schemes for oxidation of propylene to acrolein and acrylic acid have been suggested.

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.

     

A study of solid-state thermal decomposition characteristics of some metallo-organic compounds

The solid-state dehydration of the hydrated Ca(II), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) salts of pyridine-2-carboxylic acid (picolinic acid) and subsequent decarboxylation of the corresponding anhydrous salts have been studied by simultaneous TG, DTA and DTG. The sequences of thermal stability of the hydrated and the anhydrous compounds have been established from analysis of the TG, DTA and DTG traces for dehydration of the hydrated salts and for decarboxylation of the anhydrous compounds. Thermal parameters such as activation energy, enthalpy change and order of reaction for the different stages of each process have been computed by standard methods. An attempt has been made to account for the observed trend in the thermal stability of the anhydrous salts towards decarboxylation. A mechanism of thermal decraboxylation of calcium picolinate has been proposed.

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Zusammenfassung Die Dehydratisierung der hydratisierten Ca(II)-, Mn(II)-, Co(II)-, Ni(II)-, Cu(II)- und Zn(II)-Salze der Pyridin-2-carboxylsäure (Picolinsäure) in fester Phase und die nachfolgende Decarboxylierung der entsprechenden wasserfreien Salze wurden mittels simultaner TG, DTA und DTG untersucht. Aus den thermoanalytischen Kurven wurde die der thermischen Stabilität entsprechende Reihenfolge der hydratisierten und wasserfreien Verbindungen ermittelt. Thermische Parameter wie Aktivierungsenergie, Enthalpieänderung und Reaktionsordnung wurden für die einzelnen Schritte jedes Prozesses nach Standardmethoden berechnet. Es wurde ein Versuch unternommen, den Trend in der thermischen Stabilität der wasserfreien Salze gegenüber Decarboxylierung zu erklären. Ein Mechanismus der thermischen Decarboxylierung von Calciumpicolinat wird vorgeschlagen.

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

     

Thermal analysis of an epoxide resin system

TG, DTG, DTA and DSC methods were used to study the curing reaction of diglycidyl ether of bisphenol A and nadic methyl anhydride in the presence of a reactive diluent. DTG plots were used to identify the various stages of weight loss arising from volatilization of components from the resin formulation and pyrolysis of cured resin. DTA and DSC results established the temperatures at which catalysed and thermally activated cure occurred.The results demonstrate the advantages of combining thermogravimetry and differential thermal techniques to study some factors that affect resin cure and to establish the correct choice of temperature regime and catalyst.

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Zusammenfassung Die Härtung des Diglycidäthers von Bisphenol A und nadic methyl anhydrid in Gegenwart eines reaktiven Verdünnungsmittels wurde durch TG, DTG, DTA und DSC untersucht. Die verschiedenen Stadien des durch die Verflüchtigung von Komponenten der Formulierung und bei der Pyrolyse von gehärtetem Harz eintretenden Gewichtsverlustes wurden an Hand von DTG-Kurven identifiziert. Die Temperaturen, bei denen die katalytische und thermisch aktivierte Härtung einsetzt, wurden durch DTA- und DSC-Messungen ermittelt. Die Ergebnisse zeigen die Vorteile auf, die kombinierte thermogravimetrische und thermometrische Techniken bei der Untersuchung einiger die Harzbildung beeinflussender Faktoren und bei der Wahl der richtigen Temperaturverhältnisse und des Katalysators aufweisen.

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, , . , . , . , , .

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We gratefully acknowledge Harold Woodward for his support and helpful discussion.     

Temperature effect on the composition and activity of iron(III) stearate based organometallic catalysts in hydrogenation reactions

The observed temperature dependence of the composition of FeSt₃–AlEt₃ catalytic system indicates that with increasing temperature the maximum catalytic activity and the content of the associated polynuclear complex change in parallel. This complex probably plays a decisive role in catalytic processes.

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FeSt₃–AlEt₃ . . , .

     

Computation in kinetics, II. Simultaneous regression estimation of rate constants and initial concentrations

The general regression program KILET was used for simultaneous estimation of rate constants and initial concentrations. The method can be used either to improve the quality of fit calculating the possible analytical errors of some initial concentrations of a kinetic experiment or for analytical purposes, i.e. for the determination of analytes, while any side reactions can be taken into account.

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KILET - . - - , - , , .

     

Thermodynamic limitations in searching for regions of optimal performance of complex chemical reactions (exemplified by conversion of hydrocarbons)

An algorithm of searching for optimal nonequilibrium reaction mixture compositions accounting for thermodynamic limitations is suggested. It is exemplified by the analysis of a steam conversion of hydrocarbons.

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, . .

     

Electrical conductivity of liquid and film polymer composites filled with anion-radical salts in the presence of crown ethers

In the example of alkali metal tetracyanoquinodimethanides (M⁺TCQDM), a study has been made of the influence of resonance charge exchange on the conductivity () of polymer composites filled with anion-radical salts. When neutral molecules TCQDM⁰ are introduced into such systems, this leads to an increase in as a result of the lower activation energy of jumps between states TCQDM and TCQDM⁰. The addition of molecules of crown ethers has an analogous effect: They favor the appearance in the polymer matrix (the same as in solution) of TCQDM molecules in different charge states (TCQDM⁰, TCQDM) with migration of the cation within the limits of ternary associates (CE...M⁺...A) that are formed in systems for which the ratio of the crown ether cavity diameter to the cation diameter 1.4. Symbaticity has been found in the dependences of the electrical conductivity of films and the limiting mobility of solutions with the same composition on the parameter .Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 446–452, July–August, 1989.     

New method for the synthesis of 8-azasteroids: Synthesis of benzo[a]cyclohexa[f]furo[2,3-g]-quinolizines from 2-cinnamoylcyclohexa[b]oxirane

The reaction of 2-cinnamoylcyclohexa[b]oxirane with allylamine gave cis-2(),3,4a,5,6,7,8,8a()-octahydro-1-allyl-4a()-hydroxy-(2)-phenylquinolin-4-one, which upon subsequent reaction with dimethyl malonate, peroxide epoxidation, and heating with hydrochloric acid gave cis-4,5,6a(),7,8,9,10a-octa-hydro-6-allyl-20-oxo-5()phenyl-3-chlorofuro[3,2-d]quinoline. Heating of this intermediate in 96% sulfuric acid gavetrans-3a(a),7a(a),9,10(),14b(),15-hexahydro-10()-methyl-2-oxo-1-chlorobenzo[a]cyclo-hexa[f]furo[2,3-g]quitiolizine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 3, pp. 411–414, March, 1994.