Kinetics of the formation and decomposition of hydroperoxide in the oxidation of 8-pentadecanone

Kinetic parameters for the decomposition of 8-pentadecanone ketohydroperoxides in the oxidized ketone medium and the effect of caprylic acid on the rate and mechanism of hydroperoxide decomposition have been studied. The decomposition of hydroperoxide into molecular products follows mainly the ionic mechanism.

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8- . . , .

     

Correlation between apparent activation energy and selectivity in the oxidation of benzene over vanadia-molybdena catalysts

The existence of a linear correlation between the apparent activation energy of catalytic benzene oxidation and selectivity with respect to maleic anhydride was found in a series of unsupported vanadia-molybdena catalysts. A plausible explanation for such a correlation is given.

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Kinetic equation of heterogeneous catalytic isotope exchange

A kinetic equation is derived for the bimolecular isotope exchange reaction between AX _n ^* and BX _m ^o , all atoms of element X in each molecule being equivalent. The equation can be generalized for homogeneous and heterogeneous catalytic isotope exchange.

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, AX _n ^* BX _m ^o , X . , - .

     

X-ray and thermal studies of ferroelectric Dy2(MoO4)3

Dysprosium molybdate, Dy₂(MoO₄)₃, displays a ferroelectric phase transition at 145 °C. The X-ray and thermal (DTA, TG and DSC) properties of this compound have been studied. The X-ray study confirmed the ferroelectric phase in the orthorhombic space group Pba2. Thermal analysis demonstrated the existence of a ferroelectric and another phase transition in this compound.

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Zusammenfassung Dysprosiummolybdat, Dy₂(MoO₄)₃ (Abk.: DMO), ein Vertreter der Seltener-denmolybdatreihe zeigt bei 145 °C einen ferroelektrischen Phasenübergang. Röntgendiffraktion und thermische Eigenschaften (DTA, TG, DSC) der genannten Verbindung wurden untersucht. Auf Grund der Röntgendiffraktionsuntersuchung gehört die ferroelektrische Phase in die orthorhombische Raumgruppe Pba2. Mittels Thermoanalyse konnte bei dieser Verbindung die Existenz ferroelektrischer und anderer Phasenübergänge nachgewiesen werden.

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145 °C. (, ) . , Pba2. .

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The authors wish to thank Prof. A. Paul and Mr. R. Bhatnagar for their kind help in some of the experimental work. One of us (MR) gratefully acknowledges a Fellowship from DST, Government of India.     

Sulfur poisoning of Pt/Al2O3 catalysts, I. Determination of sulfur coverage by infrared spectroscopy

In the case of Pt/Al₂O₃ catalysts, a spectroscopic method was proposed to determine the amount of sulfur irreversibly bonded to platinum. Sulfate contamination of Pt/Al₂O₃ samples does not affect the metal properties for reduction temperatures lower than 300°C. Hydrogen treatment at 500°C reduces the sulfate groups into hydrogen sulfide which poisons platinum. This poisoning is strongly dependent on the metal loading. Irreversibly held sulfur sulfur corresponds to a S/Pt_s ratio close to 0.44.

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, , Pt/Al₂O₃, . Pt/Al₂O₃ 300°C. 500°C , . ⤠ . S/Pt_s, 0,44.

     

The transitions in phases II–III–IV in high purity ammonium nitrate

The phase changes in high-purity ammonium nitrate were studied by a differential thermal analysis (DTA) apparatus designed for constant heating and cooling rates and continuous cycling for 3-gram samples. On the basis of DTA and X-ray diffraction data very consistent behavior is observed. Phase IV III transformation on heating in the range 43 to 51 and Phase II IV transformation on cooling in the range 49 to 53 are demonstrated. The III II transition at about 86 is seen with repeated temperature cycling. This repeatable behavior not consistently seen by investigators using other techniques is believed to be due to the high purity material and constant heating and cooling rates.

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Zusammenfassung Die PhasenübergÄnge von hochreinem Ammoniumnitrat wurden mit Hilfe einer differentialthermoanalytischen Apparatur mit konstanten Aufheiz- und Abkühlungsgeschwindigkeiten und mit kontinuierlichen Temperaturzyklen für ungefÄhr 3 g betragende Proben geprüft. Diese Untersuchung, weiterhin röntgendiffraktometrische Aufnahmen zeigten ein sehr übereinstimmendes Verhalten. Die Phasenumwandlung IV III erfolgte beim Erhitzen zwischen 43–51, die Phasenumwandlung II IV beim Abkühlen zwischen 49–53. Die Umwandlung III II bei ungefÄhr 86 wurde im wiederholenden Temperaturzyklus beobachtet. Dieses reproduzierbare Verhalten, welches nicht mit Untersuchungen durch andere Methoden übereinstimmt, wird der hohen Reinheit der Substanzen und den konstanten Aufheiz- und Abkühlungsgeschwindigkeiten zugeschrieben.

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Résumé On a étudié les changements de phase du nitrate d'ammonium de haute pureté à l'aide d'un analyseur thermique différentiel conÇu pour réaliser des vitesses d'échauffement et de refroidissement constantes ainsi que des cycles thermiques avec environ 3 g d'échantillon. Les résultats d'ATD et de diffraction X indiquent un comportement tout à fait constant. La tranformation de la phase IV en phase III se produit entre 43 et 51 à l'échauffement et celle de la phase II en phase IV entre 49 et 53 au refroidissement. On observe la transition III II à 86 environ, avec des cycles thermiques répétés. On explique ce comportement bien défini, qui n'a pas été toujours remarqué par les chercheurs utilisant d'autres techniques, par l'emploi d'un échantillon de haute pureté et de vitesses d'échauffement et de refroidissement constantes.

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(). , , — 3 . . IVIII 43–51 C II–IV 49–53 C. IIIII 86 C . , , .

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This work was supported by the United States Atomic Energy Commission.     

Evaluation of triplet repulsion energies

The equation is suggested for predicting triplet repulsion energies. X=R–R^o, while R^o and¹V^o are the equilibrium bond length and the spectroscopic dissociation energy, respectively. Parameters and may be estimated from known bond properties.

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( X=R–R^o, a R^{o 1}V^o , . , .

     

Catalytic reactions of ethanol on H3+xPMo12?xVxO40 catalysts

The catalytic decomposition of ethanol on heteropolyacids (HPA) of the series H_3+xPMo_12–xV_xO₄₀ (x=0,1,2,3) was investigated at 240°C, using a pulse method. It has been shown that besides ethyl ether, ethylene, acetaldehyde and unreacted alcohol, a certain amount of alcohol was irreversibly sorbed by HPA. The amount of the latter decreased with x, which is considered to be due to the tighter bonding of Keggin units (KU) with an increasing number of intramolecular hydrogen bonds. The yield of ethyl ether forming at the surface was almost constant but that of ethylene and acetaldehyde decreased in the series x=0,1,2, which was connected with the increasingly difficult penetration of HPA molecules into the bulk. Some differences in the behavior of the sample with x=3 were the result of partial decomposition of this thermally stable catalyst.

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H_3+xPMo_12–xV_xO₄₀ (x=0, 1, 2, 3) 240°C. , , , , . , . , , , x=0, 1, 2, . x=3 .

     

Comparative analysis of catalytic properties of 3d metal acetylacetonates in liquid-phase oxidation of dibenzyl ether

Studies of the liquid-phase oxidation of dibenzyl ether in the presence of 12 acetylacetonates of 3d metals and a comparative analysis of the dependence of the catalytic activity and selectivity of chelates on the atomic number and valence state have been carried out.

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12 3d . .

     

Co(salen) catalyzed oxidation of oximes with t-butyl hydroperoxide

Co(salen) catalyzed the oxidation of oximes with t-butyl hydroperoxide to give the parent carbonyl compounds, providing a new convenient route to deoximation reaction. A plausible mechanism involves a substrate radical intermediate.

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Co() -, . . .