Estimation of the reactivities of some iron(III)oxides by emanation thermal analysis

A new method for estimating the reactivity of iron(III) oxide in a solid-state reaction is proposed. The method is based on the release of radioactive inert gas atoms (²²²Rn emanation) from a mixture of solids previously labeled with the inert gas atoms. By measuring the rate of release of emanation as a function of temperature, information can be obtained about the solid-state reaction and the final reaction product. The reactivities of some iron(III) oxide samples of different thermal histories and origins have been estimated in the solid-state reaction with zinc oxide labeled with the parent isotope of the emanation,²²⁸Th. The results of the proposed method, found more objective than common methods, are compared with surface area measurements on the tested samples.

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Zusammenfassung Eine neue Methode zur Abschätzung der Reaktivität von Eisen(III)oxid in der Festphasenreaktion wird vorgeschlagen. Die Methode beruht auf der Freisetzung radioaktiver Inertgasatome²²⁰Rn (Emanation) aus dem Gemisch ursprünglich mit Inertgasatomen markierter Festkörper. Durch Messung der Geschwindigkeit der abgegebenen Emanation in Abhängigkeit von der Temperatur können Informationen über die Festphasenreaktion und die Reaktions-Endprodukte erhalten werden. Die Ermittlung der Reaktivität einiger Eisen(III) oxid-Proben verschiedener Wärmegeschichte und verschiedenen Ursprungs wurde in der Festphasenreaktion mittels Zinkoxid durchgeführt, das mit dem Ausgangsisotopen der Emanation,²²⁸Th, markiert worden war. Die Resultate der vorgeschlagenen Methode, welche den üblichen gegenüber für objektiver gefunden wurde, werden mit den Oberflächenmessungen der geprüften Proben verglichen.

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Résumé On propose une nouvelle méthode pour estimer la réactivité de l'oxyde de fer(III) dans les réactions en phase solide. Elle repose sur le dégagement des atomes du gaz inerte radioactif²²⁰Rn (radon) du mélange des solides préalablement marqués par les atomes de gaz inerte. En mesurant la vitesse de dégagement du radon en fonction du temps on peut obtenir des renseignements sur la réaction dans l'état solide ainsi que sur le produit final de la réaction. On a pu estimer la réactivité en phase solide de quelques échantillons d'oxyde de fer(III), d'histoire thermique et d'origine différentes, vis-à-vis de l'oxyde de zinc marqué avec l'isotope parent du radon:²²⁸Th. On a comparé les résultats de la méthode proposée, estimée plus objective que celles habituellement utilisées, à ceux des mesures de surfaces spécifiques des échantillons étudiés.

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, . , , . : MOM, Netzch , , . - . , , , .

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Dedicated to Mrs. K. B. Zaborenko, Professor at the Moscow State University and leader of a research group developing emanation thermal analysis in the USSR, in honour of her anniversary.     

Reactivity of Cyclohexanol CH Bonds toward the tert-Butylperoxy Radical

The effect of the hydroxy group on the partial rate constants of the reactions of the tert-butylperoxy radical with CH bonds in cyclohexanol at 333 K was studied by the Howard–Ingold method. The overall reaction rate constant increased with decreasing alcohol concentration in chlorobenzene because of complex effects of hydrogen bonds at the steps of chain growth and termination. The hydroxy group activates the -CH bond and deactivates the - and -CH bonds. The reactivity of -CH bonds is close to the reactivity of CH bonds in cyclohexane.     

1,2-bis(2',6'-dimethyl-i',3'-dioxa-6'-aza-2'-silacyclooctyl-2')ethane and the corresponding ethylene and acetylene derivatives

Conclusions The reaction of 1,2-bis(methyldimethoxysilyl)ethane and the corresponding ethylene and acetylene derivatives with bis(2-hydroxyethyl)methylamine gives 1,2-bis(2,6-dimethyl-1,3-dioxa-6-aza-2-silacyclooctyl-2)ethane and the corresponding ethylene and acetylene derivatives. Analogously, 1,2-bis(vinyldimethoxysilyl)acetylene gave 1,2-bis(2-vinyl-6-methyl-1,3-dioxa-6-aza-2-silacyclooctyl-2)acetylene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1420–1421, June, 1988.     

The possibility of a simple transformation of thermogravimetric curves

A simple method is suggested for the Arrhenius-like representation of the thermal decomposition of a wide variety of materials. It consists in the transformation of the TG and the corresponding DTG curves, obtained as a single measurement by a derivative thermobalance. The method consists mainly in the division of the momentary DTG ordinates by the corresponding momentary TG values, the transformation of this value into logarithmic form, and the plotting of the logarithmic expression as a 1/T function. In many cases a straight line results testifying to a first-order reaction or a tolerable approximation of it.

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Zusammenfassung Eine einfache Methode zur Arrheniusanalogen Darstellung der thermischen Zersetzung vieler Arten von Substanzen wird vorgeschlagen. Sie besteht in der Transformierung der TG- und der entsprechenden DTG-Kurven, welche mit Hilfe einer derivierenden Thermowaage durch eine einzige Messung erhalten worden sind. Die Methode besteht hauptsächlich in der Teilung der bestehenden DTG-Ordinaten durch die entsprechenden TG-Werte, dann in der Transformierung dieses Symbols in die logarithmische Form und schließlich in der Darstellung dieses logarithmischen Ausdruckes als Funktion von 1/T, wobei in vielen Fällen eine Gerade oder eine annehmbare Näherung einer Geraden erhalten wird, die für eine Reaktion erster Ordnung spricht.

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Résumé On propose une méthode simple pour représenter la décomposition thermique d'un grand nombre de substances par une loi analogue à celle d'Arrhenius. La méthode consiste à transformer les courbes TG et TGD obtenues par une mesure unique à l'aide d'une thermobalance comportant un dispositif de dérivation. En premier lieu, on divise les ordonnées de la courbe TGD par les valeurs TG correspondantes puis on exprime ce symbole sous forme logarithmique et finalement on représente cette expression logarithmique en fonction de 1/T, ce qui donne dans de nombreux cas une droite et prouve ainsi qu'il s'agit d'une réaction du premier ordre ou d'une approximation qui peut Être tolérée comme telle.

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. , . , , , , , 1/T. , .

     

Alkyl-substituted dipyrrylmethenes and their oxa- and thia-analogs: “structure—solvation properties” correlations

New data on the spectral properties and solution enthalpies of unsymmetrically substituted 2-(alkyl-2-pyrrolylmethylidene)methylpyrrolium bromides (or ,-dipyrrylmethene hydrobromides), their ,-, ,-isomers, as well as their oxa and thia analogs, that is, 2-(2-furylmethylidene)- and 2-(2-thienylmethylidene)-3,4,5-trimethyl-1H-pyrrolium bromides, in solutions of organic solvents of different nature are presented. A decrease in the number of substituents, as well as replacement of the heteroatom (N) in one five-membered ring of the dipyrrylmetnehe by oxygen or sulfur atoms cause a monotonic hypsochromic shift of absorption bands in the electronic absorption spectrum and weakening of the chromophore properties of the compounds. The chromophore properties of isomers are weakened from the ,- to ,- and ,-dipyrrylmethenes. Main trends in the influence of structural factors on the specific features of thermooxidative destruction of the above-mentioned compounds were analyzed.     

On the poisoning effect of deuterium exchange reactions

The self-poisoning effect of deuterium exchange reactions of C₁–C₆ straight chain aliphatic hydrocarbons as well as hydrogenolysis and dehydrocyclization of n-hexane in the presence of deuterium on a nickel powder catalyst has been investigated. The poisoning is enhanced with increasing carbon number. The results can be correlated to the ease of dissociative adsorption, i. e. to the formation of multiply bonded species. A tentative model is proposed to explain the decrease of deuterium exchange in n-hexane when the reaction is shifted towards hydrogenolysis and benzene formation. It is shown that at elevated temperatures the poisoning upon deuterium exchange is caused not only by blocking of the active sites with deposits but also by hindrance of desorption of the starting molecules in the original/exchanged form.

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C₁–C₆ , - . , . , .. . - , . , , / .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Reactions of furan derivatives with aliphatic carbonyl compounds in acid medium

Sixteen new derivatives of the furan and of the 1,1-difurylmethane series were synthesized by the reactions of furan, 2-methylfuran, 2-(3-acetoxypropyl)furan, 2-(3-butyl)furan, 1-cyclopropyl-2-furylcyclopropane, and 1,1-difurylethane with saturated and , -unsaturated aliphatic carbonyl compounds in acid medium.     

Structure and reactivity of vanadium-phosphorus oxides

The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO₄·1/2H₂O(VO)₂P₂O₇+2 H₂O for VOHPO₄·1/2H₂O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different PV atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different PV ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.

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Zusammenfassung Der Beitrag thermischer Analysenmethoden zur Untersuchung der Struktur und Reaktivität von Vanadin-Phosphor-Oxiden wird erörtert. Insbesondere werden sich auf die Festkörperreaktion 2VOHPO₄.1/2H₂O(VO)₂P₂O₇+2H₂O für auf verschiedene Weise dargestelltes VOHPO₄.1/2H₂O, auf die Redox-Eigenschaften von Vanadin in Katalysatoren mit P/V-Atomverhältnissen im Bereich 0.9–1.3 und auf durch TPD bestimmte Oberflächeneigenschaften von Katalysatoren mit unterschiedlichen P/V-Verhältnissen beziehende Angaben gemacht. Zusammenhänge zwischen diesen Eigenschaften und den katalytischen Eigenschaften bei der selektiven Oxydation von n-Butan und N-Buten werden diskutiert.

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- . , VOHPO₄ · 1/2H₂O, VOHPO₄ · 1/2H₂O(VO)₂P₂O₇ + 2H₂O, - PV 0,91,3. - 1-.

     

Reactions of polyhalopyridines. 8. Reactions of polychlorotrifluoromethyl-pyridines with sodium N,N-dimethyldithiocarbamate. Structure of the 8-trifluoromethylbis-1,3-dithiolo-[4,5-b:4′,5′-e]-pyridine-2,6-dione molecule

The reaction of the isomeric tetrachloro--, -, and -trifluoromethylpyridines and of 3,4,5-trichloro-2-trifluoromethylpyridine with sodium N,N-dimethyldithiocarbamate dihydrate has been studied. In the case of the -, and -isomers an intramolecular cyclization with the formation of 1,3-dithiol-2-one derivatives occurs and the remaining compounds give only products of mono- or disubstitution of chlorine atoms by a dithiocarbamate fragment at positions 4 or 6 of the pyridine ring. The structure of the compounds synthesized was proved using¹³C NMR and X-ray crystallographic analysis.See [6] for part 7.Institute of Chemical Physics, Chernogolovka, Russian Academy of Sciences, Chernogolovka 142432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1278–1284, September, 1994. Original article submitted June 25, 1994.     

Ab initio investigation of the electron structure in bis-Cu+ acetylene and vinylidene complexes

[Cu(-C₂H₂)₂]⁺, [Cu(-CCH₂)₂]⁺ and [Cu(-C₂H₂) (-CCH₂]⁺ complexes have been studied by the ab initio double-zeta basis set method. It has been established that all calculated compounds are stable to decomposition into two C₂H₂ molecules and Cu⁺ cation and into one C₂H₂ molecules and the respective monocomplex. Calculation results suggest the possibility of intramolecular acetylene-vinylidene rearrangement in the coordination sphere of Cu⁺.

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ab initio : [Cu(-C₂H₂)₂]⁺, [Cu(-CCH₂)₂]⁺, [Cu(-C₂H₂) (-CCH₂)]⁺. C₂H₂ Cu⁺ C₂H₂ . - Cu⁺.

     

Investigation of surface phenomena on solid catalysts by simultaneous thermogravimetry and DTA

Thermogravimetry and simultaneous DTA were used to investigate the phenomena of adsorption, desorption and surface reactions on solid catalysts. The measurements were carried out with NaX and X-type ion-exchanged zeolites and silica-alumina gels (Ketjen) treated with sodium hydroxide in the presence of carbon dioxide. On the basis of the quantitative results it is possible to give an interpretation of the surface phenomena and to establish the existence of various active centres on the surfaces of the catalysts. In the case of the adsorption of carbon dioxide on X-type zeolites, the quantity of carbon dioxide adsorbed is much smaller on ion-exchanged zeolites than on NaX.

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Zusammenfassung Thermogravimetrie und simultane DTA wurden zur Untersuchung der Adsorptions-, Desorptions-Erscheinungen und Oberflächenreaktionen an festen Katalysatoren eingesetzt. Die Messungen wurden and NaX und Zeolithen des Typs X sowie an Silika-Aluminiumoxidgelen Ketjen durchgeführt, welche mit Natriumhydroxid in Gegenwart von Kohlendioxid behandelt worden waren. Aufgrund der quantitativen Ergebnisse ist es möglich eine Deutung der Oberfiächenerscheinungen zu geben und die Existenz verschiedener aktiver Zentren an der Katalysatorenoberfläche nachzuweisen. Im Falle der Adsorption von Kohlendioxid an Zeolithen des Typs X ist die Menge des adsorbierten Kohlendioxids am Ionenaustauscher viel niedriger als am NaX.

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Résumé Application de la TG et de l'ATD simultanées à l'étude des phénomènes d'adsorption, de désorption et de réactions de surface sur des catalyseurs solides. Les mesures ont été effectuées avec des zéolites échangeuses d'ions de type NaX et X ainsi qu'avec des gels Ketjen silice-alumine traités par NaOH en présence de CO₂. Les résultats quantitatifs permettent de donner une interprétation des phénomènes de surface et d'établir l'existence de divers centres actifs à la surface des catalyseurs. Dans le cas de l'adsorption de CO₂ sur les zéolites de type X, la quantité de CO₂ adsorbé est beaucoup plus faible que sur les zéolites de type NaX.

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DTA , . - NaX X - « », . . X, - , NaX.

     

Thermal conductivities of polytetrafluoroethylene and polychlorotrifluoroethylene between 4.2 and 20 K

The thermal conductivities of bulk technical samples of polytetrafluoroethylene and polychlorotrifluoroethylene were measured in the temperature range 4.2–20 K by application of the steady-state method. An interpretation of the thermal conductivity data in terms of the available theoretical and empirical models is presented.

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Zusammenfassung Die thermischen Leitfähigkeiten technischer Einzelproben von Polytetrafluoräthylen und Polychlortrifluoräthylen wurden im Temperaturbereich von 4.2 bis 20 K durch Einsatz der Festkörper-Methode gemessen. Eine Deutung der thermischen Leitfähigkeitsangaben wird anhand der zur Verfügung stehenden theoretischen und empirischen Modelle gegeben.

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4.2–20 . .

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This work was done in the International Laboratory of High Magnetic Fields and Low Temperatures, Wrocaw, Poland.     

Electronic spectra and structure of conjugate acids of carbonyl derivatives of pyrrole

The nature of the ^* transitions in the spectra of neutral molecules of - and -formyl-, acetyl-, and -carbomethoxypyrroles above 210 nm was examined on the basis of an experimental study and calculation by the Pariser-Parr-Pople (PPP) configuration interaction (CI) method. The effect of protonation on the position and intensity of the monotypic transitions was studied. The electronic structures and the energies of the neutral and all of the theoretically possible protonated forms of and -formylpyrroles were calculated within the framework of the CNDO/2 (complete neglect of differential overlap) method. The results of the calculations are in agreement with the experimental data and are in conformity with the greatest energetic advantageousness of protonation of these compounds at the oxygen atom of the carbonyl group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1221–1228, September, 1977.     

Synthesis of light alcohols from carbon monoxide and hydrogen over copper-iron catalysts

The activity and selectivity of copper-iron catalysts for the synthesis of light alcohols from carbon monoxide and hydrogen were studied. The suitable ratio of copper to iron and optimal chemical composition of the catalyst were determined.

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Photochemistry of Some Codeinones and Morphinones

Irradiation of 5-benzyl-, 5-methoxymethyl-, and 5-allyl-substituted codeinones and morphinones with UV light ( 366 nm) leads to formation of the corresponding 18-phenyl, 18-methoxy, and 18-vinyl derivatives of 4,5-epoxymethanomorphin-7-en-6-one.     

Optisch aktive aromatische Spirane, 18. Mitt.: Darstellung von optisch aktiven 4,4′-disubstituierten 2,2′-Spirobi-s-hydrindacenen

Summary All optically active title compounds were obtained from the 4,4-diacetyl-spiro compound2; (+)- and (–)-2 were accessible by chromatography on triacetyl cellulose in ethanol. The enantiomeric purities were established from chromatographic data. The chirality (–)-(2R) was deduced for all new compounds on the basis of the CD spectra of (–)-2 and (–)-2,2-spirobi-(5,6,7,8-tetrahydrobenzo[f]indane). From the molar rotations of these 4,4-disubstituted 2,2-spirobiindanes (empirical) ligand parameters were determined (using the so-called shortened approach). Generally, the values of in these compounds are higher than those of the analogous tetrahydrobenzoindane derivatives.

Herrn Prof. Dr.F. Sauter mit besten Wünschen zum 65. Geburtstag gewidmet     

An implicit heating programme to minimize the effect of the difference between the sample temperature and the programmed temperature

An implicit heating programme is suggested for minimization of the effect of the difference between the sample temperature and the programmed temperature in a thermoanalytical set-up.

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Zusammenfassung Es wird ein implizites Aufheizprogramm beschrieben, das den Einfluss des Unterschiedes zwischen Probentemperatur und programmierter Temperatur für die Probe minimalisiert.

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Theory of differential thermal analysis taking into account heat exchange between the specimen and reference cells

A basic formula of differential thermal analysis is evolved for the case when the heat transfer coefficient between the specimen cell and the reference cell is not zero. The more general formula obtained differs from the classical formula by including the parameters of the reference cell and the heat transfer coefficient between the cells. It indicates that utilization of the classical formula is not correct if heat exchange occurs between the cells. To utilize the generalized formula, additional measurements of the temperature changes of the reference material are required. However, if the time constants of the two cells are identical, the formula can be changed to assume the form of the classical formula for DTA if a correction factor is introduced which takes into account the effect of heat exchange between the cells.

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Zusammenfassung Für den Fall, dass der Übertragungskoeffizient zwischen der Proben- und der Referenzzelle nicht Zero ist, wurde eine Grundformel der Differentialthermoanalyse entwickelt. Die entstandene Formel, die vielmehr allgemein ist, weicht von der klassischen dadurch ab, dass sie auch die Parameter der Referenzzelle, und den Wärmeübertragungskoeffizient zwischen den Zellen enthält. Sie deutet darauf hin, dass die Anwendung der klassischen Formel in dem Fall nicht einwandfrei ist, wenn ein Wärmeaustausch zwischen den Zellen zustande kommt. Zur Anwendung der verallgemeinerten Formel sind weitere Messungen des Temperaturaustausches vom Referenzmaterial erforderlich. Sind aber die Zeitkonstanten der zwei Zellen identisch, kann die Formel so geändert werden, dass sie die Gestalt der klassischen DTA-Formel annimt, wenn ein, mit der Wirkung des Wärmeaustausches zwischen den Zellen rechnender Korrektionsfaktor eingeführt wird.

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, . , , . . , , , , .

     

Oxidizing properties of alumina towards alcohols. Possible reaction scheme

By chemical trapping, an acyl species has been evidenced in the oxidation of alcohols to carboxylate on an alumina surface. A possible reacton scheme is discussed.

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