Kinetics and mechanism of the oxidation of dimethyl sulfoxide by chloramine-T in hydrochloric and medium

The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine-T (CAT) in HCl medium obeys the rate law — d log [CAT]/dt=k[DMSO]^0.5[H⁺]. The active species in the oxidation is N-chloro-p-toluenesulfonamide. Chloride ion catalyzes the reaction. An order dependence of 1.7 on the gross concentration of HCl is obtained, indicating mixed order kinetics, with simultaneous catalysis by H⁺ and Cl^– ions.

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(DMSO) -T (CAT) HCl . N----. . HCl 1,7, -, .. H⁺ Cl^–.

     

Thermal stability of poly(β-bromostyrene) and copolymers of β-bromostyrene with methyl methacrylate

The thermal stabilities of poly(-bromostyrene), poly-(methyl methacrylate) homopolymers and copolymers of-bromostyrene-methyl methacrylate covering the entire composition range were studied using TG analysis. At each extreme of the composition range, incorporation of comonomer units results in a copolymer more stable than the brominated homopolymer. Maximum stability occurs for compositions of approximately 62 mole percent-bromostyrene. The formation of the anhydride structure among the degradation products leads to the stability of the copolymers.

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Zusammenfassung Die thermische Stabilität von-Bromstyrol- und Methylmethacrylat-Homopolymeren sowie von sich über den ganzen Zusammensetzungsbereich erstreckenden-Bromstyrol/Methylmethacrylat-Kopolymeren wurde thermogravimetrisch untersucht. An beiden Enden des Zusammensetzungsbereichs führt der Einbau von Komonomereinheiten zu einem Kopolymer, das stabiler als das bromierte Homopolymer ist. Maximale Stabilität wird bei einem Gehalt von etwa 62 Mol-%-Bromstyrol erreicht. Die Bildung der Anhydridstruktur führt zur Stabilität des Kopolymers.

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/-, - . , . - 62%. .

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Presented at the World Conference of Thermal Analysis, held in Bad Hofgastein (Austria), 1985.     

The apparatus function of quantitative differential thermal analysis,including heat convection and radiation

The apparatus function, i.e. the response of the equipment to a heat pulse, is derived for DTA instruments where, besides heat conduction, convection and radiation are considered. The solution of the heat-balance equation is described by a superposition of two exponential functions, which leads to the dependences of the calibration factor and the time constants on the heat capacity, the heating rate and the temperature. For the experimental determination, the relations are transformed into expressions which can easily be obtained from the calibration measurements.

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Zusammenfassung Die Apparatefunktion, das ist die Reaktion der Anordnung auf einen Heizimpuls, wird für eine Differential-Thermo-Anlage abgeleitet, wobei neben Wärmemeitung auch -Konvektion und-Strahlung zugelassen sind. Die Lösung der Wärmebilanzgleichung wird durch die Überlagerung zweier Exponentialfunktionen beschrieben, wobei sich die Anhängigkeiten des Gerätefaktors und der Zeitkonstanten von der Wärmekapazität, der Heizrate und der Temperatur ergeben. Zur experimentellen Bestimmung werden die Ausdrücke zu leicht aus den Kalibrierungsmessungen zugänglichen Größen aufbereitet.

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— , , , . , , . , .

     

Kalorische Exzeßcharakteristik flüssiger Nichtelektrolyt-systeme

Zusammenfassung Die mittleren molaren Exzeßenthalpien der ternären Systeme Benzol /n-Heptan/n-Tetradecan, Benzol/n-Decan/n-Tetradecan und Benzol/Toluol/n-Tetradecan sowie die der korrespondierenden binären Systeme wurden titrationskalorimetrisch bei 298.15 K über den gesamten Molenbruchbereich bestimmt. Auf der Grundlage dieser experimentellen Ergebnisse sollte die Anwendbarkeit des Gruppenlösungsmodells von Ratcliff u.a. zur Vorausberechnung mittlerer molarer Exzeßenthalpien an ternären Gemischkombinationen getestet werden. Die Abweichung zwischen den gemessenen und inkrementell berechneten Mischungsenthapien lag bei den hier untersuchten Systemen im Bereich von 0 bis 12%.

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Via a titration calorimetric method the molar enthalpies of mixing for the three ternary systems benzene/n-heptane/n-tetradecane, benzene/n-decane/n-tetradecane and benzene/toluene/n-tetradecane, as well as for all of the corresponding binary systems, were measured over the whole range of mole fractions at 298.15 K. On the basis of the experimental results the applicability of the Group Solution Model, proposed by Ratcliff et al. for predictive calculations of heats of mixing, was tested for the treatment of ternary systems mentioned above.The differences between the measured and incrementally calculated heats of mixing were found to range from 0 to 12 %.

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Résumé Les enthalpies de mélange des trois systèmes ternaires benzène/n-heptane/n-tétradécane, benzène/n-décane/n-tétradécane et benzène/toluène/n-tétradécane ont été mesurées ainsi que celles des systèmes binaires correspondants, à 298.15 K dans le domaine complet des fractions molaires, par une méthode de titrage calorimétrique. En se fondant sur les résultats expérimentaux, on examine la possibilité d'appliquer aux systèmes ternaires, tels que ceux mentionnés ci-dessus, le modèle proposé par Ratcliff et al. pour prévoir les chaleurs de mélange. L'écart entre les chaleurs de mélanges mesurées et celles calculées par incréments varie de 0 à 12%.

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, /-/- , /-/- //- , 298,15 . , , . . 0 12%.

     

Unusual selectivity in photooxygenation of alkanes by air in CH3CN solutions catalyzed by CrCl3?C6H5CH2N(C2H5)3Cl

A new system CrCl₃–C₆H₅CH₂N(C₂H₅)₃Cl–CH₃CN for photooxygenation of alkanes is suggested. Unlike metal chlorides and oxocomplexes, it oxidizes alkanes to produce ketones and small amounts of alcohol. Adding of benzene, methylene chloride or ethanol to the cyclohexane solution rises the oxygenation rate and changes the ketone/alcohol ratio. With small amounts of hydroquinone the formation rate of cyclohexanone (but not of cyclohexanol) sharply decreases. Kinetic isotope effect in the oxidation of C₆H₁₂ and C₆D₁₂ is 1 for cyclohexanol and 2.9 for cyclohexanone. Cyclohexanol formation is assumed to follow a mechanism that does not involve free radicals. Free radicals can participate in the route toward ketone.

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CrCl₃–C₆H₅CH₂N(C₂H₅)₃Cl–CH₃CN . , . , /. ( ) . C₆H₁₂ C₆D₁₂ 1 2,9 . , , . , .

     

Activation of dinitrogen molecule on the surface of iron (or ruthenium) based catalysts

Supported iron (or ruthenium) catalysts prepared by different methods were tested in the ammonia synthesis reaction. A promoter effect of potassium was observed in these catalysts. By means of infrared spectroscopy, the activation of dinitrogen species was observed on the surface of a highly dispersed 3.2 wt. % Ru-alumina non-promoted catalyst.

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( ), , . . (3,2 . % — ) .

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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, H⁺. . , , , .

     

Effect of supports on the energetics of CO chemisorption on rhodium catalysts

The kinetics of adsorption-desorption processes were measured using Frequency Response Chemisorption for CO on supported Rh catalysts. Measurements on Rh/SiO₂ failed to give a signal, most likely due to the strong natures of the CO sorption on the metal. CO on Rh/TiO₂ measurements indicated the existence of one molecularly adsorbed state. The rate constants for adsorption state were derived.

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- CO Rh . Rh/SiO₂ , - CO . Rh/TiO₂ . .

     

High activity of MgO catalyst prepared from magnesium oxalate for the hydrogenation of butadiene

High activity of magnesium oxide prepared by thermal decomposition of magnesium oxalate for the hydrogenation of 1,3-butadiene has been examined by XPS and IR, together with the isomerization of 1-butene. XPS spectra of MgO differed from those of two other MgO catalysts. With Ar etching, the binding energies of Mg2p and 01s shift, which is related to the surface basicity. Both basic and acidic sites are responsible for hydrogenation, but isomerization proceeds only on basic sites.

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, 1,3- 1-, . MgO ; Ar 2p 1s Mg, . , , , - .

     

Temperature effects on the fluorescence kinetics of excited cyclohexane

In agreement with the results reported by Lipsky, emission from cyclohexane depends on the temperature T and on the nature of the phase (liquid or solid). Determination of the lifetimes of the fluorescent state with a single photon counting apparatus gives similar results. Our experimental work shows that the rate constant of fluorescence for the solid phase I (face-centered cubic cell) practically does not depend on temperature. Variations of lifetime vs. T cannot easily be interpreted only with the classical theory of non-radiative transitions.

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, , ( ). , , . , I ( ) . .

     

Temperature dependence of the X-ray induced adsorption of oxygen and methane on ZnO

The capacity of ZnO with respect to the photo- and X-ray adsorbed, as well as postadsorbed oxygen is shown to depend on the temperature. It is suggested that this dependence cannot be attributed to either the thermal annealing of the induced sites or the thermal desorption of the adsorbed molecules.

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O , - , , , . , .

     

Physical properties of the catalyst used for partial oxidation of anthracene to anthraquinone. II. Electron paramagnetic resonance study

Electron paramagnetic resonance studies on intermediates and final active catalyst material used for partial oxidation of anthracene to anthraquinone are reported.

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, .

     

Kinetics and mechanism of oxidation of methanol by acid bromate

The kinetics of oxidation of methanol by bromate ion in hydrochloric acid medium has been investigated. A mechanism consistent with the experimental observations is suggested.

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. , .

     

A new concept explaining catalytic synergy between two solid phases

We propose a new mechanism for explaining the synergy between MoS₂ and Co₉S₈ in hydrodesulfurization. We suppose that spill-over hydrogen produced by Co₉S₈ exerts an effect ofremote control on the active center of MoS₂, a slight reduction leading to hydrogenation centers and stronger reduction to hydrodesulfurization centers.

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MoS₂ CoS₈ . , , CO₉S₈, MoS₂, , , , .

     

Methanol-based synthesis of hydrocarbons on bifunctional Y-type zeolites

The directions of methanol conversion on Pt, Pd, Zn, Ni metals and Y zeolites and on bifunctional metal-Y-zeolite catalysts have been studied. The increase of the hydrogenation activity of bifunctional catalysts enhances the rate of methanol conversion and decreases the selectivity of hydrocarbon formation.

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- Y, - Y.

     

Solvation corrections to the Br?nsted equation for general base catalysis

A quantitative allowance for the solvation corrections f^solv eliminates deviations from the Brönsted lines for the bases OH^–, H₂O, and primary and secondary amines and straightens these lines for known base-catalysed reactions.

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f^solv OH^–, H₂O, .

     

Unimolecular decomposition of CF3OF-calculation by reduced Kassel integral in factorized form

The fall-off curves were calculated for the unimolecular decomposition of the trifluoromethyl hypofluorite at 475.8, 496.9 and 507.3 K by means of the Reduced Kassel Integral in Factorized Form.

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475,8,496,9 507,3 .

     

Comparison of dynamic mechanical and dielectric thermal analysis on cure studies for composites

Dielectric measurements covering a wide frequency range provide one of the few practical methods for monitoring the cure of thermosets (epoxy, etc.) using relatively non-intrusive sensors. The measurements form the basis of a manufacturing control cycle, in the autoclave, provided the rheological state of the thermoset can be related to the dielectric constant (¹) and loss factor (tan). The present paper concerns further investigations in our laboratory of the correlation between mechanical and dielectric behaviour during cure (1).

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Zusammenfassung Dielektrische Messungen über einem weiten Frequenzbereich stellen die eine Methode dar, um unter Anwendung verhältnismässig nicht-intrusiver Fühler die Aushärtung von Duroplasten /Epoxid usw./ verfolgen zu können. Die Messungen bilden die Grundlage für einen Pertigungsüberwachungskreis des Autoklaven, da der rheologische Zustand des Duroplast mit der Dielektrizitätskonstanten // und dem dielektrischen Verlustfaktor /tan/ in Verbindung gebracht werden kann. Vorliegende Arbeit berichtet über weitere Untersuchungen unseres Laboratoriums über den Zusammenhang zwischen mechanischem und dielektrischen Verhaltens während der Aushärtung.

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120–230°. 2 3590 . . . 150°, . .

     

Is the ion-linear quadrupole capture rate constant anisotropic with respect to the sign of the product of the charge on the ion and the quadrupole moment of the molecule?

The sign of the charge-quadrupole moment product is shown to affect the rate of ion-linear quadrupole capture.

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- .

     

Experimental setup to study catalysts by combined pulse microcatalytic and ESR spectroscopic methods

A setup consisting of an ESR spectrometer and a pulse microcatalytic installation is suggested for simultaneous kinetic and spectral measurements directly in catalytic processes.

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- , , .