On the formation mechanism of hexafluoropropylene oxide in low-temperature liquid-phase oxidation of hexafluoropropylene by molecular oxygen

The effect of initiation rate (dose-rate of -radiation) on the formation rate of hexafluoropropylene oxide has been studied. Experimental data confirm that the epoxide forms in the reaction R–O–C₃F ₆ ^· R^·+C₃F₆O, as contrasted to the generally accepted fragmentation of -peroxyalkyl radicals R–O–O–C₃F ₆ ^· RO^·+C₃F₆O.

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( -) . , , R–O–C₃F₆R+C₃F₆O R–O–O–C₃F₆RO+C₃F₆O.

     

Influence of SO 4 2− doping and Y-irradiation on the thermal decomposition of barium bromate

The effects of SO ₄ ^2– doping and Y-irradiation on the isothermal (563 K) decomposition of barium bromate have been investigated gasometrically with a vacuum apparatus. Plots of the fraction decomposed avs. timet for pure, doped and irradiated crystals exhibited characteristic stages: initial gas evolution (initial puff), an induction period, linear reaction, an acceleratory period and decay. The data are considered in the light of various kinetic models, e.g. linear rate equation, Prout-Tompkins and Avrami-Erofeev. The plausible mechanism of the reaction and the effects on this of anion vacancies and Y-irradiation are discussed briefly.

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Zusammenfassung Die Wirkung von Versetzen mit SO ₄ ^2} - und -Bestrahlung auf die isotherme (563 K) Zersetzung von Bariumbromat wurde gasometrisch untersucht. Es zeigte sich, daß die Zeitcharakteristiken für die reinen, die versetzten und bestrahlten Kristalle verschiedene Stufen durchlaufen, nämlich anfängliche Gasentwicklung (Aufblähen), Induktionsperiode, lineare Reaktion, Beschleunigung und Abklingen. Die Daten wurden unter dem Gesichtspunkt verschiedener kinetischer Modelle betrachtet, z. B. lineare Geschwindigkeitsgleichung, das Modell von Prout-Tompkins und Avrami-Erofeev. Es werden kurz ein einleuchtender Reaktionsmechanismus und der Einfluß von Anionengitterlücken und -Bestrahlung darauf diskutiert.

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- (563 ) . , ,-, «t» , , , , , . , - -. .

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The authors thank the Department of Atomic Energy, Government of India, for financial support. M.K.S. also gratefully acknowledges the award of a Research Fellowship by the same agency, which made the work possible.     

Stoichiometry as canonical transformation of chemical kinetics

Applying the apparatus of differential manifolds and that of classical conservative point mechanics, it is shown that stoichiometry plays the role of canonical transformations in chemical reaction kinetics.

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, , .

     

Studies of copper-modified V?Mo oxide catalyst for acrolein oxidation to acrylic acid

Modification of a V–Mo oxide catalyst by copper improves its catalytic properties due to the formation of a variable composition V–Cu–Mo–O phase with varying the ratio Mo/Me (Me=V+Cu).

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T–Cu–Mo–O, Mo/Me, Me=V+Cu.

     

Potential for coal calorific value corrections,dependent on the carbonate mineral type present

In addition to calcite, other carbonate minerals in coal all undergo endothermic reactions on heating, i.e. dolomite, ankerite, siderite, aragonite, magnesite, rhodochrosite, witherite and strontianite. Of these, when determined in air, siderite and rhodochrosite give small exothermic resultants, while the amount of Fe in ankerites affects the actual endothermic values obtained. The magnitude of these carbonate decomposition reactions can be shown by DTA to be different and will need to be allowed for individually in calorific value corrections of coals containing them.

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Zusammenfassung Nicht nur Kalkspat, sondern auch andere in Kohle vorkommende Karbonatmineralien wie z. B. Dolomit, Ankerit, Spateisenstein, Aragonit, Magnesit, roter Braunstein, Witherit und Strontionit gehen bei Erhitzen endothermische Reaktionen ein. Von diesen zeigen Spateisenstein und roter Braunstein exotherme Ergebnisse kleinen Wertes, während der Betrag an Eisengehalt in Ankeriten den jeweils gemessenen endothermischen Wert beeinflußt. Das Ausmaß dieser Karbonatzersetzungsreaktionen kann durch DTA-Messungen als unterschiedlich nachgewiesen werden und muß bei den Kaloriewertkorrektionen für Kohlen, die diese Mineralien enthalten, berücksichtigt werden.

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

     

Temperature programmed desorption (TPD) of carbon monoxide from cobalt surfaces

Three different binding states of CO on cobalt surfaces have been identified by TPD studies. The energetics of these adsorption states and their relevance in Fischer-Tropsch synthesis are considered.

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CO - . -.

     

Thermal stabilities of new complexes of magnesium nitrate,acetate and phosphate with amide ligands

The thermal decompositions of complex compounds of magnesium nitrate, acetate and phosphate with urea, acetamide and formamide ligands were investigated by means of simultaneous TG-DTA. The thermal stabilities of the complexes depend on the natures of the anions and the amide ligands.

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Zusammenfassung Die thermische Zersetzung der Komplexverbindungen von Magnesiumnitrat-,acetat und -phosphat mit Harnstoff, Acetamid und Formamid wurden durch simultane TG-DTA untersucht. Die thermische Stabilität der Komplexe hängt von den Anionen des Salzes und den Amidliganden ab.

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-,- , . , .

     

Stoichiometric coefficients as chemical charges

Thermodynamic charge is one of the central concepts in the thermokinetic theory of physico-chemical processes. This paper demonstrates that stoichiometric coefficients play the role of charges in elementary chemical reactions.

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- . , .

     

The influence of CSH phase nuclei on Ca3SiO4Cl2 hydration

The influence of CSH phase nuclei on calcium chlorosilicate hydration has been studied by means of calorimetry, QXRD, DTA and TG methods.

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Zusammenfassung Mittels kalorimetrischen, QXRD-, DTA- und TG-Verfahren wurde der Einfluß von CSH Phasenkörpern auf die Hydratierung von Kalziumchlorosilikat untersucht.

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, , .

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C=CaO, S=SiO₂, H=H₂O     

Stereoselectivity observed in cross metathesis of cis- and trans-2-butene with 1-butene over Re2O7/Al2O3 catalyst

Cross metathesis of cis- and trans-2-butene with 1-butene was studied over Re₂O₇/Al₂O₃ catalyst in a recirculation system at 313 K. Formation of ethylene and hexenes was inhibited by 2-butenes; formation of propene and pentene proceeded without induction from trans- and with induction from cis-2-butene and 1-butene. Selective formation of trans-2-pentene was observed from trans-2-butene, but no such selectivity was characteristic for cis-isomers.

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- -2- 1- Re₂O₇/Al₂O₃ 313 . 2-; - -2- 1-. -2 -2-, , - .

     

Silylation of porous glass supported platinum catalysts

Effect of silylation with hexamethyldisilazane on adsorption and catalytic properties of porous glass-supported platinum catalysts has been studied. Catalytic activity decreases markedly with an increase in surface coverage by trimethylsilyl groups for all the following reactions examined: hydrogenation of benzene, dehydrogenation of cyclohexane and dehydrocyclization of n-hexane.

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, . , : , -.

     

Thermal analysis of conducting polymers part I

Thermogravimetry (TG) has been conducted on a series of electroconducting acid-doped polyanilines. The weight loss results suggest that the majority of dopants are eliminated between 230 °C to 350 °C leaving behind the skeletal non-conducting polyaniline. The doped polyaniline are thermally more stable than the pristine polyaniline in air at high temperatures. This suggests that despite the early elimination observed, the presence of dopant at the begining has a stabilizing effect on the skeletal polyaniline. By comparison the acid-doped polyanilines are more thermally stable than many other electroconductive polymers, such as polypyrroles and polyacetylenes.

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Zusammenfassung An einer Reihe von elektrisch leitenden säureversetzten Polyanilinen wurden thermogravimetrische (TG) Untersuchungen durchgeführt. Die Gewichtsverluste zeigen, daß die Mehrzahl der Zusätze bei einer Temperatur zwischen 230 °C und 350 °C eliminiert werden, wobei die nichtleitenden Polyaniline zurückbleiben. Bei hohen Temperaturen ist das versetzte Polyanilin in Luft thermisch stabiler als das ursprüngliche Polyanilin. Das bedeutet, daß eine anfängliche Gegenwart der Zusätze ungeachtet der frühen Eliminierung einen stabilisierenden Effekt auf das Polyanilingerüst ausübt. Im Vergleich erwiesen sich säureversetzte Polyaniline als thermisch stabiler als andere elektrisch leitende Polymere wie z. B. Polypyrrole oder Polyazethylene.

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, . , 230–350°, . , . , , . , - , , , .

     

State of molybdenum in silica-molybdenum oxide catalysts

In the synthesis of silica-molybdenum oxide catalysts by spray drying of an aerosol suspension in an aqueous ammonium paramolybdate a silicamolybdenum heteropolyacid (SMA) is formed which is not decomposed up to 500–600°C due to stabilization of the heteropolyanion by the support surface.

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, 500–600°C .

     

Synthesis of dimethyl sulfide in the presence of zeolites

In the presence of zeolites, dimethyl sulfide is produced either through CH₃OH interaction with H₂S or via CH₃SH decomposition. In accordance with their activities, in both reactions, zeolites arrange in the same sequence: HZSMHNaY>NaXNaY. Realization of the reaction CH₃OH+H₂S is more difficult compared to methanethiol decomposition.

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CH₃OH H₂S CH₃SH. : HZSMHNaY>NaXNaY. CH₃OH+H₂S , .

     

Vapor phase oxidation of 2-methylpyridine on vanadyl polyphosphates

Vanadyl -and -polyphosphates in vapor phase oxidation of 2-methylpyridine show comparable activity and selectivity to the formation of pyridine-2-carboxaldehyde as traditional vanadium-molybdeum oxide catalysts. A redox mechanism for the reaction of 2-methylpyridine oxidation on vanadyl polyphosphates is suggested with interaction between 2-methylpyridine and oxygen of the catalyst lattice as the rate-determining step.

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- - 2- -- . - 2- . - 2- .

     

Thermal behaviour of melamine

Melamine undergoes condensation on heating with elimination of ammonia and formation of insoluble products. Thermogravimetry and infrared characterisation show that two products of successive condensation can be reproducibly obtained upon heating atT}<500 °C and then at 600 °C. Above 620 °C, the melamine condensate undergoes thermal degradation with quantitative formation of volatile products.

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Zusammenfassung Melanin geht beim Erhitzen eine Kondensation unter Abgabe von Ammoniak und Bildung unlöslicher Produkte ein. Durch Thermogravimetrie und Infrarotspektroskopie wird gezeigt, daß beim Erhitzen zwei Produkte von aufeinanderfolgenden Kondensationsreaktionen beiT}<500 °C undT= 600 °C reproduzierbar erhalten werden. Oberhalb 620 °C wird das Melaminkondensat vollständig unter Bildung flüchtiger Produkte thermisch zersetzt.

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. , . , 500°, — 600°. 620° .

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The authors wish to thank Dr. N. Del Fanti of Mantefluos, Italy for most helpful discussion.

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This work has been supported by the Consiglio Nazionale delle Ricerche through the Progetto Finalizzato Chimica Fine e Secondaria.     

CO and NO adsorption on photoreduced Mo/SiO2 catalysts

CO and NO adsorption on photoreduced Mo/SiO₂ catalysts has been studied by IR and mass-spectrometric methods. Products of interaction between adsorbed molecules and surface molybdates of various structures have been identified.

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- - CO NO CO Mo/SiO₂ . .

     

Thermoanalytical investigations of some industrial wastes produced in steel works

The experiments involves three types of industrial wastes produced by iron works, which create serious hazards to the natural environment: (1) paint-shop sludge, (2) oil-polluted diatomite, and (3) oil-polluted scale. The choice of an appropriate and safe storage method should be based on extensive physicochemical examination.DTA, in combination with other data, allows characterization of the combustible properties of wastes. Thermoanalytical measurements were carried out in a dynamic air atmosphere. Enthalpy values were calculated from peak areas of DTA curves. Thermoanalytical data were compared with calorimetric results obtained with an oxygen bomb.

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Zusammenfassung Drei Arten industrieller Abtälle eines Stahlwerks, die schwere Umweltbelastungen darstellen, wurden untersucht: (1) Lackiererei-Schlamm, (2) ölhaltiger Diatomit, (3) ölhaltiger Kesselstein. Geeignete sichere Deponien setzen ausführliche physikalisch-chemische Untersuchungen voraus. DTA in Kombination mit anderen Untersuchungen erlaubt die Charakterisierung der Verbrennungseigenschaften der Abfälle. Die thermoanalytischen Untersuchungen erfolgten im Luftstrom, die Verbrennungswärmen wurden aus den DTA-peak-Flächen berechnet. Die Ergebnisse werden mit denen kalorimetrischer Messungen in einer Sauerstoffbombe verglichen.

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- , . , . , - . . . . , .

     

High resolution solid state1H NMR spectra of hydroxy groups in aluminas

Using magic angle spinning technique, the¹H NMR spectra of surface hydroxy groups of different alumina modifications (-, -, and -Al₂O₃) have been studied. Several types of hydroxy groups that differ in their chemical shifts are tentatively attributed to different types of coordination of OH groups to aluminium atoms.

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¹H (-, -, -Al₂O₃). , , , .