On the mechanism of alcohol insertion into the carbonyl group in the coordination sphere of Fe(III) tris-hexafluoroacetylacetonate

The kinetics of formation of hemiacetals in the Fe(III) coordination sphere resulting from the reaction of Fe(III) tris-hexafluoroacetylacetonate with methanol has been studied by the stopped-flow method. Two molecules of methanol and coordinated hexafluoroacetylacetonate anion (HFA^–) take part in the rate-determining step. The effect of the second molecule of alcohol can be attributed to catalysis of proton transfer from methanol to the HFA^– ligand through the chain of hydrogen bonds in 6-membered cyclic structures.

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stopped-flow Fe(III). , -. , , .

     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

Aromatization of propylene and butadiene over MoO3?SiO2 and WO3?SiO2 catalysts

The activity of various MoO₃–SiO₂ and WO₃–SiO₂ catalysts for the aromatization of propylene and butadiene has been investigated. The results obtained show a comparatively high aromatization activity of the catalysts for propylene to benzene and toluene. The direct conversion of butadiene to ethylbenzene, using WO₃ on acid treated silica, is considered to be an alternative reaction pathway to the known metathesis step to ethylene and benzene.

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MoO₃–SiO₂ WO₃–SiO₂ . . , WO₃ .

     

Steady state kinetic equation for SO2 oxidation on vanadium catalysts

From the analysis of the detailed reaction mechanism and taking into account vanadium complex formation processes, a steady state kinetic equation has been derived to describe experimental data in a wide range of reaction conditions.

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, .

     

Enantioface-differentiating transfer hydrogenation of ethyl acetoacetate on modified Raney nickel

Ethyl acetoacetate was hydrogenated on tartaric acid-NaBr-modified Raney nickel in the presence of isopropanol as hydrogen source—the first example concerning the asymmetric transfer hydrogenation using a chiral modified metal catalyst.

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, — NaBr — . , .

     

Thermal decomposition of tetraamineplatinum(II) chloride by simultaneous TG/DTG/DTA/MS and direct insertion probe mass spectrometry

Simultaneous thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), and evolved gas analysis (EGA) by mass spectrometry (MS) have been used to determine the decomposition path for tetraamineplatinum(II) chloride and cis- and trans-diamineplatinum(II) chloride. Unequivocal identification of the evolved gases was done by direct insertion probe mass spectrometry.The thermal decomposition of (NH₃)₄PtCl₂ occurred in two steps. The first was endothermic loss of two moles of ammonia producing a mixture of cis- and trans-diaamineplatinum(II) chloride. The second step was decomposition of the diamine complex to metallic Pt and N₂, HCl, and NH₄Cl. Reduction of Pt(II) to metallic Pt was coupled with oxidation of ammonia to molecular nitrogen and protons.

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Zusammenfassung Simultane Thermogravimetrie (TG), derivative Thermogravimetrie (DTG), Differentialthermoanalyse (DTA) und Analyse der entwickelten Gase (EGA) durch Massenspektrometrie (MS) wurden zur Bestimmung des Reaktionsverlaufs bei Zersetzung von Tetraminplatin(II)-chlorid sowie cis- und trans-Diaminplatin(II)-chlorid herangezogen. Die eindeutige Identifizierung der entwickelten Gase erfolgte durch Massenspektrometrie mit direkter Probeneinführung. Die thermische Zersetzung von (NH₃)₄PtCl₂ erfolgt in zwei Schritten. Der erste ist die endotherme Abspaltung von zwei Mol Ammoniak unter Bildung eines Gemisches von cis- und trans-Diamin-platin(II)-chlorid. Der zweite Schritt ist die Zersetzung des Diaminkomplexes zu metallischem Pt, H₂, HCl und NH₄Cl. Die Reduktion von Pt(II) zu metallischem Pt ist mit der Oxydation von Ammoniak zu molekularem Stickstoff und Protonen gekoppelt.

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-, -, -, - - (II) - (II) . (II). -. (NH₃)₄PtCl₂ . - -(NHN₃)₂PtCl₂. , , . .

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The technical assistance of G. J. Dechert is gratefully acknowledged.     

Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride

The influence of some irregularities in polystyrene (PS) and polyvinyl chloride (PVC) chains on their thermal stability was investigated. UV irradiation caused an increase in the content of these irregularities in the polymers. It was found that the presence of carbonyl groups and crosslinking of the polymer chains hamper the thermal dehydrochlorination of PVC and the total decomposition of both polymers. On the other hand, weak peroxy linkages (which facilitate degradation processes) and conjugated double bonds decrease the temperature of total decomposition of PS and PVC blends.

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Zusammenfassung Es wurde der Einfluß von Unregmlmäßigkeiten in Polystyrol (PS)- und Polyvinylchlorid (PVC)-Ketten auf deren thermische Stabilität untersucht. UV-Bestrahlung verursacht ein Ansteigen des Gehaltes an Unregelmäßigkeiten in den Polymeren. Es wurde festgestellt, daß die Gegenwart von Carbonylgruppen und Querverbindungen der Polymerketten die thermische Dehydrochlorierung von PVC und eine vollständige Zersetzung beider Polymere verhindern. Andererseits senken Peroxidverknüpfungen (die die Degradierungsvorgänge erleichtern) und konjugierte Doppelbindungen die Temperatur für eine vollständige Zersetzung von PS und PVC Gemischen.

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. - . , . , , , .

     

Effect of nickel on the hydrogenating activity of MoS2

The activating effect of nickel on MoS₂ impregnated with an aqueous solution of Ni(CH₃COO)₂ and sulfided has been established to be proportional to the amount of active nickel incorporated as Ni²⁺ cations in the MoS₂ lattice. MoS₂ capacity for active nickel is limited and determined by the preparation method of the parent MoS₂.

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MoS₂ ( Ni(CH₃COO)₂, ) Ni²⁺, . MoS₂ «» .

     

Catalyst deactivation in toluene steam dealkylation

Two deactivation factors of Rh/-Al₂O₃ catalysts in toluene steam dealkylation are examined: deactivation during working and sulfur poisoning. Onstream deactivation is only due to coke deposit. Specific activity per free exposed fraction of the metal is constant. Sulfur is a strong non-selective poison which may hinder coke formation.

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Rh/-Al₂O₃ : . . . , .

     

NO adsorption on tin(IV) oxide

The adsorption of NO on SnO₂ has been studied in the temperature range from 0 to 86°C, at pressures from 0.4 to 3.5 Torr. The adsorption isotherms are described by the Freundlich equation. The rate of adsorption obeys the Roginskii-Zeldovitch equation and decreases with increasing temperature. The reduction of SnO₂ with carbon monoxide results in a drop in the adsorption rate and in the amount of adsorbed NO.

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NO SnO₂ 0°–86°C 0,4–3,5 . . - . SnO₂ NO.