Propos sur l'interpretation de l'energie d'activation experimentale

Résumé Les résultats de divers travaux montrent que la valeurE _e de l'énergie activation expérimentale tirée des diagrammes d'Arrhénius varie avec la pression, dans le cas de réactions de décompositions endothermiques.L'analyse de divers modèles permet d'expliquer cette constatation en montrant que la grandeurE _e n'a pas le sens d'une énergie d'activation mais est une fonction de nombreux paramètres. Deux d'entre eux ont été retenus dans le cadre de cette étude: le terme d'écart à l'équilibre et le terme de gradient thermique, provoqué par l'endothermicité du phénomène.Cette analyse permet d'établir une prévision de la fonctionE _e (P) conforme aux résultats expérimentaux.

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The results from various investigations show that the experimental activation energy valueE _e derived from the Arrhenius diagrams varies with pressure for endothermic decomposition reactions.The analysis of various models allows this fact to be accounted for by showing thatE _e should be regarded not in its fundamental formulation, but as being a function of numerous parameters. Two of these were taken into account in the present study, i.e. deviation from equilibrium and a thermal gradient due to the fact that the phenomenon is endothermic.FunctionE _e (P) fitting the experimental results may be predicted by such an analysis.

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Zusammenfassung Die Ergebnisse verschiedener Untersuchungen zeigen, dass die aus den Arrhenius-Diagrammen abgeleiteten experimentellen Werte der AktivierungsenergieE _e bei endothermen Zersetzungsreaktionen mit dem Druck variieren.Die Analyse verschiedener Modelle ermöglicht eine Erklärung dieser Tatsache, indem gezeigt wird, dassE _e nicht in ihrer grundliegenden Formulierung betrachtet werden darf, sondern als Funktion einer Anzahl von Parametern. Zwei dieser Parameter wurden in der vorliegenden Untersuchung berücksichtigt d.h. die Abweichung von dem Gleichgewicht und der thermische Gradient, welcher infolge der endothermen Beschaffenheit der Erscheinung auftritt.Eine den Versuchsergebnissen entsprechende FunktionE _e (P) kann mittels einer solchen Analyse vorausgesagt werden.

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, _e, , . , _ee , . , : , , . _e (), , .

     

Effect of preparation conditions on the properties of carbon-supported nickel catalysts

Carbon-supported Ni catalysts were prepared from nickel nitrate or chloride. Characterization was carried out by H₂ and CO chemisorption, XRD and TEM. Catalysts were further tested in the hydrogenolysis of n-butane.

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, , . H₂ CO, ., -.

     

Thermal and some other properties of the complexes crystallizing from the system Ni(II)-en-[Ni(CN)4]2−-H2O

Seven complex compounds exhibiting the compositions Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) and-Ni(en)₂Ni(CN)₄ (VII) were prepared from the system Ni-en-[Ni(CN)₄]^2–-H₂O. These compounds were examined by the methods of infrared spectroscopy, X-ray powder diffractometry, UV-VIS reflectance spectroscopy, and also by the measurement of magnetic moments. The thermal stability, the stoichiometry of thermal decomposition and the mutual transformations were investigated with a derivatograph. The reactions proceeding according to the following schemes were observed if the system was heated to appropriate temperature: (I)(II)(III)(V)(IV) and (VI)(VII)(III)(V)(IV) Process (VII)(III) represents isomerization. The reversibility of the process (V)(IV) is due to the high hygroscopicity of the anhydrous complex. The changes in structure in the course of the individual processes are discussed.

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Zusammenfassung Aus einem System Ni-en-[Ni(CN)₄]^2–-H₂O wurden sieben Komplexe der Formeln Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) und-Ni(en)₂Ni(CN)₄ (VII) hergestellt. Diese Verbindungen wurden mittels IR-Spektroskopie, Röntgenpulverdiffraktometrie, UV-Reflexionsspektroskopie und durch Messungen des magnetischen Momentes untersucht. Die Wärmestabilität, die Stöchiometrie des thermischen Zerfalles und die gegenseitigen Umwandlungen wurden mittels eines Derivatographen untersucht. Wird das System auf geeignete Temperaturen erhitzt, kann der Reaktionsverlauf durch folgendes Schema dargestellt werden: (I)(II)(III)(V)(IV) und (VI)(VII)(III)(V)(IV).Der Prozeß (VII)(III) verkörpert eine Isomerisierung. Die Umkehrbarkeit von Prozeß (V)(IV) ist auf die ausgeprägten Hygroskopieeigenschaften des wasserfreien Komplexes zurückzuführen. Es werden die im Ablaufe der einzelnen Prozesse vorgehenden Strukturveränderungen besprochen.

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Ni- -[No(N)]² -₂ Ni(en)₃Ni(CN)₄ · ₂ (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄-2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2,5H₂O (VI) -Ni(en)₂Ni(CN)₄ (VII). , , - , . , . (I)(II)(III)(V)(IV) (VI)(VII)(III)(V)(IV). (VII)(III) . (V)(IV) . .

     

Reactivity of electronically excited Br(2P1/2) atoms towards CH3F

The rate constants for Br(²P_1/2) and Br(²P_3/2) atoms in the reaction Br+CH₃FHBr+CH₂F in photobromination of CH₃F have been determined. Their ratio is 10^{–(2.6±0.5)} exp(10100±1000/RT) in the temperature range of 60–200 °C.

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Br(²P_1/2) Br(²P_3/2) Br+CH₃FHBr+CH₂F CH₃F. 60–200 °C 10^{–(2,6±0,5)} exp (10100±1000/RT).

     

Differential thermal analysis studies on the crystallization of strontium tungstate from sodium tungstate melt. Nucleation mechanism and induction periods

The nucleation mechanism, kinetics and induction periods in strontium tungstate crystallization from sodium tungstate melt in platinum crucibles were investigated by differential thermal analysis. Heterogeneous nuclei first formed on the metal platinate particles within the solution during the induction periods (¯t); the main crystal growth started only after ¯t and few new nuclei were then formed. At any crystallization temperature, ¯t varied inversely with the cooling rate (R _T), and with the rate (R_C) of development of excess solute concentration according to the relation ¯t = 1/(k ₁ R _c ), wherek ₁ and are constants. The critical temperature (¯T), critical supersaturation(¯ S), k ₁ and were evaluated.

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Zusammenfassung Der Keimbildungsmechanismus, sowie die Kinetik und die Induktionsperioden wurden bei der Kristallisation von Strontiumwolframat aus Natriumwolframatschmelzen in Platintiegeln durch Differentialthermoanalyse untersucht. Die heterogenen Kristallkeime wurden zuerst während der Induktionsperiode () an den Metallplatinat-Teilchen in der Lösung gebildet: das Hauptkristallwachstum begann erst nach und nachfolgend wurden einige neue Keime gebildet. Bei jeder Kristallisationstemperatur änderte sich umgekehrt proportional zu den Abkühlungsgeschwindigkeiten (R _T) und den Geschwindigkeiten (R _c) der Bildung überschüssig gelösten Materials, entsprechend der Gleichung = 1/(k ₁ R _c , wobeik ₁ und Konstanten sind. Die kritische Temperatur (¯T), die kritische Übersättigung (¯S),k ₁ und wurden bewertet.

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Résumé On a étudié par analyse thermique différentielle le mécanisme de nucléation ainsi que la cinétique et les périodes d'induction de la cristallisation du tungstate de strontium, à partir des bains fondus de tungstate de sodium, dans des creusets de platine. Des noyaux hétérogènes se forment d'abord sur les particules de platinate métallique dans la solution, au cours des périodes d'induction (): la croissance principale des cristaux ne commence qu'après et il se forme alors quelques noyaux nouveaux. A une température quelconque de cristallisation, varie de façon inverse avec les vitesses de refroidissement (R _T) et les vitesses de développement (R _c ) de concentrations de sursaturation de la substance en solution, selon la relation = 1/(k ₁ R _c , oùk ₁ et sont des constantes. On a évalué la température critique (¯T), la sursaturation critiques (¯S),k ₁ et.

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, . - (¯ t). ¯t . - ,¯t (R _T), (R _c) ¯t=1/(K₁ R _c ), ₁ — . (¯), (_-S), K₁ .

     

Rearrangement ofα -trifluoromethyl-β-dialkylamino-β-fluoroacrylic acid N.N-dialkylamides

Conclusions When heated in the presence of a catalytic amount of BF₃ etherate,-trifluoromethyl--diethylamino--fluoroacrylic acid N, N-dimethylamide is reversibly isomerized to-trifluoromethyl--dimethylamino--fluoroacrylic acid N, N-diethylamide. The methyl esters of-trifluoromethyl--diethylammo--fluoroacrylic acid and-trifluoromethyl--phenoxy--fluoroacrylic acid N,N-dimethylamide are not isomerized under the same conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.1, pp.137–141, January, 1976.     

μSr studies of free radicals in the gas phase

Muonium (Mu=₊+e^-) is the bound state of a positive muon and an electron. Since the positive muon has a mass about 1/9 of the proton, Mu can be regarded as an ultra light isotope of hydrogen with unusually large mass ratios (MuHDT=1/9123). The muon spin rotation technique (SR) relies on the facts that (1) the muon produced in pion decay, ^{+ +} + , is 100% spin polarized and (2) the positron from muon decay is emitted preferentially along the instantaneous muon spin direction at the time of the muon decay.In transverse field SR (TF-SR), the precession of the muon spin in muonium substituted radicals is directly observed by detecting decay positrons time differentially. From observed radical frequencies, the hyperfine coupling constants (A ) of C₂H₄Mu, C₂D₄Mu,¹³C₂H₄Mu, C₂F₄Mu, and C₂H₃FMu are determined. In the longitudinal field avoided level crossing (LF-ALC) technique, one observes the resonant loss of the muon spin polarization caused by the crossing of hyperfine levels at particular magnetic fields. The LF-ALC method together with the information onA obtained from TF-SR allows one to determine the magnitude and sign of the nuclear hyperfine constants at - and -positions. Results are compared with hydrogen substituted ethyl-radicals and isotope effects are discussed.     

Interaction of styrene with triphenylphosphinecobalt complexes

The interaction of the cobalt phosphine complexes Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ and H₃Co(PPh₃)₃ with styrene yields mono and dinuclear complexes identified by the ESR method. A paramagnetic complex, Co(PPh₃) (styrene)₂, is one of the intermediates in the catalytic hydrogenation of styrene.

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Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ H₃Co(PPh₃)₃ . , Co(PPh₃) ()₂.

     

Temperature programmed desorption of NH3 and H2O from NH4NaX and CoNH4NaX zeolites

A study has been made of temperature programmed desorption (TPD) of NH₃ and H₂O from samples of NH₄X and CoNH₄X zeolites of various degree of exchange. NH₃ TPD peaks could be explained by interaction of NH₃ with different Brönsted and Lewis acidic centers. Moreover a water peak at high temperatures allowed interpretations of the dehydroxylation, and by reason of the characteristic desorption temperatures a particular state of the Co²⁺ ions in the CoNH₄X zeolites is postulated.

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- () NH₃ H₂O NH₄X CoNH₄X . NH₃ NH₃ =qs . . Co²⁺ CoNH₄X.

     

Structures of some lilioglycosides from the bulbs ofLilium regale

Six steroid glycosides, which gave been called lilioglycosides B, C, E, F, H, and I have been isolated from fresh bulbs ofLilium regale Wills. The structure of each compound has been determined by methods of physicochemical analysis. This is the first time that lilioglycosides B, C, H, and I, have been described; they are, respectively: (25S)-spirost-5-ene-3,27-diol3-O--D-glucopyranoside; (25R)-spirost-5-ene-3,27-diol3-O--D-glucopyranoside27-(3-hydroxy-3-methylglutarate); (25S)-spirost-5-ene-3,27-diol3-O-{[O--L-rhamnopyranosyl-(12)],[O--D-glucopyranosyl-(13)]--D-glucopyranoside}; and (25S)-spirost-5-ene-3,27-diol 3-O-{[O--L-rhamnopyranosyl-(12)],[O--D-glucopyranosyl-(13)]-O--D-glucopyranoside} 27-[(S)-3-hydroxy-3-methylglutarate].Institute of Genetics, Academy of Sciences of the Republic of Moldava, 2002, Kishinev, ul. Padurilor, 20. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 841–847, November–December, 1997.     

Thermal decomposition of some homobinuclear dihalide-bridged iron(III) complexes

Thermal studies by TG and DTG on some homobinuclear dihalide-bridged iron(III) complexes of the general type [Fe(S₂CNR₂)₂X]₂(}-X ₂) were carried out in air and nitrogen atmospheres. The apparent activation energies were determined by graphical methods and the TIN temperatures were calculated from the TG profiles. Finally, a possible mechanism of the decomposition is suggested on the basis of the pyrolysis and mass spectral data.

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Zusammenfassung Einige homobinukleare Eisen(III)-Komplexe mit Dihalidbrücken der allgemeinen Formel [Fe(S₂CNR₂)₂X]₂(–X₂) wurden mittels TG und DTG in Luft und Stickstoffatmosphäre untersucht. Die scheinbaren Aktivierungsenergien wurden nach graphischen Methoden aus den TG-Profilen bestimmt. Ein möglicher, auf pyrolytischen und massenspektrometrischen Daten basierender Zersetzungsmechanismus wird vorgeschlagen.

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[Fe(S₂CNR₂)₂X]₂ (-₂) . , . - .

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Thanks are due to Dr. G. Karagiannidis, Laboratory of Organic Chemical Technology, Aristotelian University, for technical assistance.     

Charge control in the formation of complexes of phenol with unsaturated compounds containing organometallic substituents from group IV

The resonance donor effect of the , conjugation of R₃M and R₃MCH₂ (M = Si, Ge, Sn; R is an alklyl group) substituents with the triple bond in compounds R₃MC=CX and R₃MCH₂CCX (X = H, R) changes on passing from isolated molecules to their H-complexes. A partial ⁺ charge on the triple bond enhances , conjugation; a partial ^– charge on the triple bond has practically no effect on the resonance properties of R₃M substituents, whereas the , conjugation of R₃MCH₂ substituents diminishes owing to the effect of negative direct resonance interaction. The effect of , conjugation on the effective negative charges of the carbon atoms in the -CC- fragments was estimated quantitatively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041–1046, June, 1994.This work was supported by the Russian Fundation for Basic Research (Grant 93-03-18372).     

Kinetics of oxidation of carbonyl compounds by peroxomonosulfate. Formaldehyde, formic acid and formate anion

Kinetics of oxidation of formaldehyde, formic acid and formate anion by peroxomonosulfate (PMS) were studied. Formaldehyde is oxidized both by HSO ₅ ^– and SO ₅ ^2– , whereas formic acid and formate ion are oxidized by SO ₅ ^2– alone. The kinetic results show that the formaldehyde is 10³ times more reactive than formic acid, which in turn reacts 10² times faster than formate anion. Mechanisms are discussed in terms of the kinetic results.

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, . HSO ₅ ^– , SO ₅ ^2– , SO ₅ ^2– . , . 10³ , , , , . 10² , . .

     

Changes in the surface characteristics of residues from the thermal decomposition of nickel oxysalts

The changes in surface area and density which occur during the decomposition of eight nickel oxysalts have been reported. Surface area peaks were observed in the temperature range 473 K to 673 K. An equation relating to the number of product particles (n) produced from a single particle of original material has been derived. Logn was shown to vary linearly with temperature, wheren is the number of product particles formed from one original reactant particle.

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Zusammenfassung Es wird über die Veränderungen der Oberfläche und Dichte berichtet, welche bei der Zersetzung von acht Nickeloxysalzen auftreten. Oberflächenpeaks wurden im Temperaturbereich von 473 K bis 673 K beobachtet. Eine Gleichung wurde abgeleitet, welche sich auf die Zahl (n) der sich aus einem einzigen Partikel der Ausgangssubstanz bildenden Produktpartikel bezieht. Es wurde bewiesen, daß sich logn linear zur Temperatur ändert, wobein die Zahl der sich aus einem reagierenden Ausgangspartikel bildenden Produktpartikel ist.

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Résumé Etude des changements de surface spécifique et de densité pendant la décomposition de huits oxysels du nickel entre 473 K à 673 K. En désignant parn le nombre de particules issues d'une particule unique du matériau initial, on montre que logn varie linéairement avec la température.

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8 - , . , , 473–673 . , (), . logn .

     

Spin conversion of positronium in paramagnetic solutions studied by age-momentum-correlation method

Correlated measurement of the lifetime and of the lineshape of the 511 keV annihilation radiation of positrons (age-momentum correlation, AMOC) has become a powerful tool for investigating reactions of positron or positronium in condensed matter as a function of time. The beam-based ⁺ AMOC method installed at the Stuttgart relativistic positron beam facility (E _kin ^e+ 4MeV) offers substantial advantages over the conventional E coincidence technique resulting in a fast data taking due to the unity detection efficiency of the ⁺ scintillator which provides the start signal for the lifetime measurement. In this paper the application of AMOC to positronium chemistry is illustrated by the study of spin conversion of positronium in the system methanol/HTEMPO as a function of HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, a paramagnetic solute) concentration. The same technique can be applied to other systems and other reactions in positronium chemistry, e. g., oxidation or complex formation.     

Identification of exchange-coupled V4+ and Cu2+ ions in Cu?V?Mo oxide systems

ESR studies of X(CuO)·V₂O₅·8.3 MoO₃ (X=1–2) calcined in flowing nitrogen at 250–350 °C have revealed the exchange interaction of Cu²⁺ and V⁴⁺ ions that form a paramagnetic system.

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X(CuO) V₂O₅·8,3 MoO₃, X=1–2, , 250–350°C, Cu²⁺ V⁴⁺, .

     

Thermal properties of elastin-fatty acid complexes

Differential scanning calorimetry has been applied to study the interaction of fibrous or of soluble elastin with fatty acids and their trialanine derivatives. The DSC curves of elastin-fatty acid preparations exhibited an endothermic transition in the temperature range - 10° to + 50°. The peak temperatures and the enthalpy changes were independent of the chain length and of the saturation of the fatty acid. The interaction with the trialanine derivatives was similar to that with the fatty acids.Such interactions between elastin and lipids might take place in vivo as well, resutling in the loss of elasticity of elastin fibres and consequently in the development of arteriosclerotic lesions.

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Zusammenfassung Zur Untersuchung der Wechselwirkung zwischen dem fibrösen oder lösbaren Elastin, und den Fettsäuren und ihren Trialanin-Derivaten wurde die DSC-Methode angewandt. Die DSC-Kurven der Elastin-Fettsäure-Präparate zeigten in dem Temperaturbereich von - 10° bis + 50° einen endothermischen Übergang. Die Peak-Temperaturen und die Änderungen der Enthalpie waren von der Kettenlänge und der Sättigung der Fettsäure unabhängig. Die Wechselwirkung mit den Trialanin-Derivaten war der mit den Fettsäuren ähnlich.Solche Wechselwirkungen zwischen Elastin und den Lipiden können auch in vivo stattfinden, und die Abnahme der Elastizität der Elastin-Fibern, und folglich die Entfaltung der arteriosklerotischen Schädigungen resultieren.

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. - — — 10° - + 50°. , . , . , , .

     

Influence of carbon dioxide on the position of oxygen adsorption equilibrium on silver

Due to interaction with carbon dioxide, when some adsorbed oxygen atoms on silver surfaces are converted into carbonate groups, the binding energy diminishes and the volatility of adsorbed oxygen rises.

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, , .

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .