Thermal analysis of heterocyclic thione donor complexes. Part 1

The thermal decomposition of the Co(II) complexes of 1-methylimidazoline-2(3H)-thione (MImt), general formula Co(MImt)₂X₂ (X=Cl, Br & I), have been studied in air and argon by means of TG and DTG as well as in nitrogen by DTA. Quantitative DTA has been used to derive reaction enthalpies (H _R) from the melting and decomposition endotherms in nitrogen. Decomposition processes have been proposed for the complexes in air and in inert atmospheres. A mean coordinate bond dissociation energy (¯D) has been estimated for the Co-MImt bond in Co(MImt)₂Cl₂.Reaction end products in air have been identified by X-ray powder diffraction.

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Zusammenfassung Die thermische Zersetzung von Kobaltkomplexen des 1-Methylimidazolin-2(3H)-thions (IMmt) der allgemeinen Formel Co(MImt)₂X₂ (X=Cl, Br, J) wurde in Luft und Argon mittels TG und DTG und in Stickstoff mittels DTA untersucht. Reaktionsenthalpien (H_r) wurden durch quantitative DTA aus den in Stickstoffatmosphäre erhaltenen endothermen Schmelz- und Zersetzungspeaks erhalten. Es wurden Mechanismen für die Zersetzungsprozesse der Komplexe in Luft und inerter Atmosphäre vorgeschlagen. Die mittelere Dissoziationsenergie (¯D) der koordinativen Bindung Co—MImt in Co(MImt)₂Cl₂ wurde bestimmt.In Luft erhaltene Reaktionsendprodukte wurden durch Röntgenpulverdiffraktometrie identifiziert.

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1- -2()- () ()₂₂, X=l, I, , . (H _R) . . - ()₂l₂. , , - .

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The author is grateful to Mr. J. R. Creighton, Newcastle upon Tyne Polytechnic, for technical assistance with this work and to Dr. F. Buttler, Teesside Polytechnic for mass spectral data and helpful discussion.     

Quantum yields of the mercury photosensitized cis-trans isomerization of 1,3-pentadiene

The quantum yields of thecis trans andtrans cis Hg 6(³P₁) photosensitized isomerizations of 1,3-pentadiene at 100 Torr and 22°C are 0.54±0.02 and 0.42±0.02, respectively. The steady state ratio ([trans]/[cis])_ss is 1.27±0.05 which is almost identical with the ratio of the quantum yields, (ct)/(tc)=1.29±0.10. Thecistrans isomerization is suggested as a useful actinometer for mercury sensitized reactions.

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Hg 6(³P₁) 1,3- 100 22°C 0,54±0,02 0,42±0,02, . ([]/[]) 1,27±0,05, ( )/( )=1,29±0,10. , .

     

Non quasi-stationary state pyrolysis. Induction period of neopentane pyrolysis

The principle of an apparatus using an isothermal continuous flow stirred tank reactor to study homogeneous gas phase reactions at space times of the order of 1 sec is given. With this apparatus, the induction period of neopentane pyrolysis (as an example) has been clearly shown.

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, , 1 . , , .

     

Cerium (IV) exchange in mordenite

X-Ray diffraction analysis, surface acidity (Hammett method), H₂O and CO₂ adsorption of cerium(IV) exchanged H-mordenite are reported.

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- , ( ) H₂O CO₂ H-, Ce(IV).

     

Hydrocondensation of CO on iron-alumina catalysts. Influence of ethylene

The transformations of H₂/C₂H₄ and H₂/C₂H₄/CO mixtures on activated and carbided 10% Fe/Al₂O₃ catalysts have been studied in terms of the role of ethylene in Co hydrocondensation, and specifically its influence on the selectivity to C₃–C₄ hydrocarbons.

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H₂/C₂H₄ H₂/C₂H₄/CO 10% Fe/Al₂O₃ CO C₃–C₄ .

     

Simultaneous adsorption of CO and O2 on Ni(100) plane at low temperatures

LEED, AES and TPD studies of CO adsorption at 170 K on the oxygen-covered surface of Ni(100) have revealed its great amount throughout the range of oxygen coverage. With thermal desorption from a mixed layer the appearance of CO₂ due to the reaction CO_ads+O_ads, indicates that a part of oxygen adsorbed on Ni(100) at T=170 K is reactive.

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, () CO 170 Ni(100). . CO₂ Co+ +O, , Ni(100) T=170 .

     

On the poisoning effect of deuterium exchange reactions

The self-poisoning effect of deuterium exchange reactions of C₁–C₆ straight chain aliphatic hydrocarbons as well as hydrogenolysis and dehydrocyclization of n-hexane in the presence of deuterium on a nickel powder catalyst has been investigated. The poisoning is enhanced with increasing carbon number. The results can be correlated to the ease of dissociative adsorption, i. e. to the formation of multiply bonded species. A tentative model is proposed to explain the decrease of deuterium exchange in n-hexane when the reaction is shifted towards hydrogenolysis and benzene formation. It is shown that at elevated temperatures the poisoning upon deuterium exchange is caused not only by blocking of the active sites with deposits but also by hindrance of desorption of the starting molecules in the original/exchanged form.

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C₁–C₆ , - . , . , .. . - , . , , / .

     

Permanganate oxidations in strongly basic solutions

In strongly basic solutions the permanganate ion oxidation of C₁ and C₂ alcohols, aldehydes and acids obeys a second-order kinetic law of the type rate=k_o [S]_o [MnO ₄ ^– ], where S is the substrate. The rate constant k for both alcohols and aldeydes is proportional to the OH^– ion concentration. This behavior is interpreted in terms of a deprotonation equilibrium followed by rate-determining hydride ion transfer to MnO ₄ ^– .

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, C₁ C₂ W=k_o [S]_o [MnO ₄ ^– , S — . OH^–. MnO ₄ ^– , .

     

Reforming type Pt/Al2O3 catalyst prepared from [(CH3)3PtX]4 complexes by thermal decomposition

Pt/Al₂O₃ catalysts with good reforming activity were prepared from [(CH₃)₃PtX]₄ (X=Cl, Br, I) complexes and tested in pulse and continuous-flow reactors in n-hexane dehydrocyclization. It has been demonstrated that [(CH₃)₃PtX]₄ complexes are excellent precursors of supported platinum catalysts.

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Pt/Al₂O₃ [(CH₃)₃ PtX]₄ (X=Cl, Br, I) -. , [(CH₃)₃PtX]₄ .

     

Triterpene Glycosides and Their Genins from Tragacantha stipulosa. Structure of Cyclostipuloside C

A new cycloartane glycoside of the cyclostipuloside C series, 3-O--D-xylopyranoside-6,16-di-O--D-glucopyranoside-20S-24R-epoxycycloartan-3,6,16,25-tetraol is isolated from aerial organs of Tragacantha stipulosa Boriss.     

Selective catalytic hydrogenation of double bonds in unsaturated furan ketones

In the hydrogenation of unsaturated furan ketones in solvents at atmospheric pressure and room temperature the Raney Pd–Al catalyst is highly active and selective towards the hydrogenation of double bonds. The only reaction products are the respective saturated ketones.

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, Pd–Al . . .

     

Influence of Cr loading on the catalytic properties of CrO3/SiO2 catalysts in 2-propanol conversion

Catalytic activity of CrO₃/SiO₂ samples for 2-propanol conversion is governed by only a small amount of active centers (estimated to be around 10¹⁷ per gram of catalyst), whereas excess chromium neither develops catalytic activity nor inhibits the reaction on the active sites. Only when the chromium loading is high enough to allow formation of bulk-like agglomerates (5 wt.% Cr) is 2-propanol converted also on this CrO_x surface phase, but with a significant higher activation energy.

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CrO₃/SiO₂ 2- ( 10¹⁷ ), . , - (5 .% Cr), 2- CrO_x , .

     

Kinetic equations of isotope redistribution in an elementary reaction

Kinetic equations for the redistribution of isotopic molecules in an elementary reaction have been derived on the basis of atom distribution matrices.

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.

     

Coke deposition on naphtha reforming catalysts: II. Influence of the addition of a second metal to platinum

The nature and rate of coke deposited on mono-and bimetallic reforming catalysts have been studied for normal heptane reforming. For bimetallic catalysts it has been shown that coke deposition is less extensive than on monometallic catalyst, depending on the degree of polymerization and the type of bimetallic catalyst.

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-. , , , .

     

Thermal behaviour of acidic salts of mixed tetravalent metals

The results of investigations on intercalated crystalline zirconium phosphate are described in the literature. The behaviour of crystalline phosphates containing both zirconium and titanium metal ions has not been investigated previously. Within these investigations, the thermal behaviour of such materials has been studied in the temperature interval 25–1000 °C by simultaneous recording of TG, DTG and DTA curves. The results are presented in this paper.

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Zusammenfassung Ergebnisse über Untersuchungen an in Schichten eingelagerten kristallinen Zirkoniumphosphat sind in der Literatur beschrieben. Das Verhalten kristalliner Phosphate, die sowohl Zirkoniumals auch Titanmetallionen enthalten, wurde bis jetzt nicht untersucht. Als Teil dieser Untersuchungen wurde das thermische Verhalten solcher Materialien im Temperaturbereich 25–1000 °C durch simultanes Registrieren der TG-, DTG- und DTA-Kurven näher bestimmt, dessen Ergebnisse hier dargelegt werden.

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. , . , , 25–1000°. .

     

Collisional energy transfer in the decomposition of 2-methyloxetane and 3-methyloxetane, I. Gas/gas collisions

The pressure dependence of the unimolecular rate constants for the thermal decomposition of 2-methyloxetane and 3-methyloxetane has been studied. The average energy transferred downward in gas-gas collision was determined by the application of RRKM theory and a stepladder model of energy transfer.

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2- 3-. , - , .

     

High-temperature pyrolysis of polymers

The experimental results on the pyrolysis of thermoplastic polymers under high-temperature heating and burning conditions are discussed. The reaction of polymer degradation in this case proceeds in the same way as in a low-temperature region.

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Zusammenfassung Die experimentellen Ergebnisse der Pyrolyse von thermoplastischen Polymeren unter Erhitzungs- und Brehnbedingungen hoher Temperatur werden besprochen. Die Reaktion der Polymerzersetzung verläuft in diesem Falle genau so wie in der Niedrigtemperaturzone ab.

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. , .

     

Acid strength distributions in the Mo?Al?Si and the Ni?Mo?Al oxide systems determined by ammonia adsorption

Acid strength distributions of Mo–Al–Si and Ni–Mo–Al oxide systems have been found by means of a relationship that gives pK_a values from amounts of ammonia adsorption. Molybdenum is suggested to cause a homogenization in the acid strength distribution of alumina but a heterogenization in silicaalumina, whereas nickel is found to neutralize strong acid sites inherent to molybdenum.

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Mo–Al–Si Ni–Mo–Al , . , , .

     

Effect of free phosphine on the reactivity of phosphine-containing rhodium(I) complexes

The photolysis products of SO₂-pentane-NO mixtures are N₂O, H₂O and a compound designated as RNO. Kinetic data obtained by OC method confirm the previously proposed scheme of photolysis. Also studied was the photolysis of SO₂, NO and cyclohexane mixtures. From comparison of spectral characteristics of RNO and its analog 2-methyl-2-nitrosopropane, the probable structure of RNO is suggested.

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SO₂--NO N₂O, H₂O , RNO. , , . SO₂ NO . RNO 2--2- RNO.

     

Oxidative dehydrogenation of n-butenes: Product effect in the reactions over tin-antimony mixed oxides

The addition of possible oxidation and/or isomerization products (butadiene, water, isomeric n-butenes) resulted in neither promotion nor inhibition in the oxidative dehydrogenation of n-butenes over tin-antimony mixed oxide catalysts. On the basis of these and other information on the influence of products an interpretation has been given to complete the reaction mechanism more realistic than those based on previous experimental results.

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(, ) ( -) , . , , .