Kinetics and mechanism of the permanganate oxidation of trans-crotonic acid

The kinetics and intermediates of the permanganate oxidation of trans-crotonic acid have been investigated in the pH range of 0.5–5.0 using the stoppedflow technique. The formation of manganese(III) as a short-lived intermediate has been established. The reaction is first order with respect to both MnO ₄ ^– and crotonic acid (crotonate). The resolved rate constants at 25°C are 730 and 410 M^–1 sec^–1 for the acid and the anion, respectively. The reaction mechanism is discussed.

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pH=0,5–5,0, . (III) . MnO ₄ ^– , (). 25°C 730 410 M^{–1 –1} , . .

     

Kinetics of Cr(VI) and V(V) oxidation of trans-stilbene and indene

Title reactions are acid catalyzed and strongly dependent on the permittivity of the medium. With Cr(VI) indene reacts faster than trans-stilbene, but with V(V), trans-stilbene reacts faster than indene. The mechanism is discussed.

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. Cr(VI) , -, V(V) - , . , .

     

Characterization of MoS2/SiO2 by ESR and NO adsorption

Six MoS₂/SiO₂ samples were characterized by XRD, BET surface area, ESR and NO adsorption measurements. Correlation was found between the amount of Mo⁵⁺, sulfur radicals and adsorption capacity for oxygen and NO.

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MoS₂/SiO₂ , , , NO. Mo⁵⁺, NO.

     

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. , .

     

On the dissociation mechanism of carbonates and their isomorphous mixture

The thermal decomposition processes of carbonate minerals are analyzed by comparison of the notions on chemical bonds in crystals and modern concepts on solid-phase reactions. It is shown that depending on the mechanism of thermal dissociation, the carbonate minerals most widespread in nature may be divided into two groups: first, CaCO₃, SrCO₃ and BaCO₃, characterized by decomposition temperatures close to the equilibrium values and undergoing recombination on cooling; and second, MgCO₃, MnCO₃, FeCO₃ and ZnCO₃, with dissociation temperatures exceeding the equilibrium values by 250° and recombining only at high partial pressures of CO₂ (above 1000 bar).

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Zusammenfassung Die thermischen Zersetzungsprozesse von Carbonatmineralien wurden auf der Basis der Vorstellungen über die chemischen Bindungen in Kristallen und moderner Konzeptionen über Festphasenreaktionen analysiert. Es wird gezeigt, dass die in der Natur weitverbreitetsten Carbonatmineralien, abhängig vom Mechanismus der thermischen Zersetzung, in zwei Gruppen unterteilt werden können: die erste umfasst CaCO₃, SrCO₃ und BaCO₃ und ist durch Zersetzungstemperaturen nahe den Gleichgewichtswerten und durch Rekombination beim Abkühlen charakterisiert, zur zweiten gehören MgCO₃, MnCO₃, FeCO₃ und ZnCO₃ mit Dissoziationstemperaturen, die die Gleichgewichtswerte um etwa 250° überschreiten, und die nur bei hohen CO₂-Partialdrücken (über 1000 bar) rekombinieren.

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, . , , . CaCO₃, SrCO₃, BaCO₃ , . MgCO₃, MnCO₃, FeCO₃, ZnCO₃ , 250°, ( 1000 .).

     

Toluene disproportionation and coke formation over fluorided alumina and hydrogen-mordenite

Toluene transformation was investigated on a fluorided alumina and a protonic mordenite under hydrogen (0.8, 12 bar) and under nitrogen (12 bar). Hydrogen pressure considerably improves the catalytic stability of H-mordenite by inhibiting the formation of coke. Moreover, hydrogen eliminates part of the coke deposited by reaction under nitrogen, and regenerates the activity of the mordenite. On the contrary, hydrogen has no effect in the case of fluorided alumina. The particular behavior of the mordenite is attributed to its very strong acidity.

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(0,8, 12 ) (12 ). -, . , , , . , - . .

     

Preparation of catalysts by spray decomposition

Spray decomposition of solutions is an uncommon but very promising technique for the preparation of multicomponent solid systems with welldefined structure. The experimental arrangement is described and a summary of the systems prepared until now is given. These are MgO–ZnO, CaO, CdO, Al₂O₃. Fe₂O₃ solid solutions and CdO. CdSO₄ and Al₂O₃. Al₂(SO₄)₃ systems.

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, , . : MgO·ZnO, CaO·CdO,. Al₂O₃·Fe₂O₃ CdO·CdSO₄ Al₂O₃·Al₂ (SO₄)₃.

     

Some remarks about butene-1 transformations on NaHY zeolite

Comments are given on the paper Alternative Interpretation of Infrared Spectra of the Zeolite NaHY+Butene-1 System of Forster and Seelemann /2/. Our previous paper /1/ was partly revised but the usefulness of comprehensive studies by infrared and temperature-programmed desorption methods has been emphasized.

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: NaHY+-1. [2]. [1] , - .

     

Kinetic studies of methanethiol disproportionation

Kinetic regularities in catalytic disproportionation of methanethiol to dimethyl sulfide and hydrogen sulfide have been studied in a flow circulation reactor. A kinetic equation is suggested to describe the reaction on inhomogeneous surfaces.

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- - . , .

     

Novel type of oscillatory chemical reactions

Chemical oscillations occur during the uncatalyzed oxidation of a number of phenol and aniline derivatives by acidic bromate.

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