Control of the non-crystallinity of miokamycin (9,3″-diacetylmidecamycin) by differential thermal analysis

A mixture of 9,3-diacetylmidecamycin with 9.1% (by weight) ethylcellulose is used for its antibiotic properties, but it is only active in a non-crystalline state, which is a glassy one: DTA showsT _g at 99<T°C< 106.DTA has been used to develop a quantitative method of non-crystallinity control based upon' a linear relation between the crystallinity percentage and the computed algebraic sum of the enthalpies of recrystailization and fusion.It is shown that for binary mixtures with liquidus-type melting curves this procedure is to be preferred to the measurement of recrystailization enthalpy vs. crystallinity percentage.

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Zusammenfassung Ein Gemisch von 9,3-piacetylmidecamycin mit 9,1 Gew.-% Ethylcellulose wird wegen dessen antibiotischen Eigenschaften angewandt, ist aber nur im nicht-kristallinen, glasigen Zustand aktiv. DTA ergibt fürT _g99<T°C<106. Die DTA wurde zur Entwicklung einer quantitativen Methode zur Kontrolle der Nicht-Kristallinität herangezogen, die auf einer linearen Beziehung zwischen dem in % ausgedrückten Kristallinitätsgrad und der berechneten algebraischen Summe der Rekristallisations- und Schmelzenthalpie beruht. Es wird gezeigt, daß bei binären Mischungen mit Schmelzkurven des Liquidustyps diesem Verfahren gegenüber der Messung der Rekristallisationsenthalpie in Abhängigkeit vom Kristallisationsgrad der Vorzug zu geben ist.

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9,3- 9,1 % _g , , 99<T°< 106°. , . , , .

     

Study of the steps of acrolein oxidation over a vanadium-molybdenum catalyst

Acrolein is oxidized to acrylic acid over a V–Mo catalyst by lattice oxygen, while the formation of CO₂ also involves gas phase oxygen. The steady state of catalyst reduction is about 5% monolayer and is characterized by an oxygen binding energy of 61 kcal/mol.

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V–Mo- , CO₂ . 5% 61 /.

     

Experimental study of the initial stage of Li2SO4·H2O single crystal dehydration in vacuum

The initial stage of the Li₂SO₄·H₂O single crystal isothermal dehydration has been studied by means of quartz crystal microbalance. As found, weight loss in the initial process may be considered as H₂O molecule diffusion from a semiinfinite medium. The numerical values of the H₂O molecule diffusion in Li₂SO₄·H₂O have been calculated from the results obtained.

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. - - - -. - Li₂SO₄·H₂O.

     

Rate constants for the reaction of singlet oxygen with diazocompounds

Rate constants for the reaction of singlet oxygen with a series of diazocompounds and diazoketones have been measured. Diazoketones were found to possess lower reactivity than diazocompounds.

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- . , .

     

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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, .

     

Preparation and properties of borosilicates with a zeolite structure

The dependence of the state of boron atoms on the preparation conditions of borosilicates and the effect of this state on their catalytic properties in methanol conversion have been studied.

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, .

     

Kinetic analysis of thermal dehydration and hydrolysis of MgCl2·6H2O by DTA and TG

The thermal decomposition of MgCl₂·6H₂O (non-dried and partly dried) and the kinetics of the process were studied by DTA, TG, DTG, IR, X-ray diffraction and chemical analysis of Mg and Cl. The reactions which occurred in the course of the thermal analysis were identified as dehydration (in steps), thermal hydrolysis of MgCl₂·H₂O and dehydrochloridization of magnesium hydroxy chlorides. Melting of the phases MgCl₂·6H₂O, MgCl₂·4H₂O and MgCl₂ was also identified in the thermal curves. Thermal weight loss continued up to 800 °C in flowing air or nitrogen, but only up to 700 °C in static air. MgO was the end-product of thermal treatment in both cases.The kinetic parameters of the reaction, the activation energyE, pre-exponential factorA and apparent order of reactionb, were computed by several methods. The activation energy and the apparent reaction order of dehydration were found to increase with decreasing hydration number of the Mg. The dehydrochloridization process had the highest activation energy.

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Zusammenfassung Die thermische Zersetzung von MgCl₂·6H₂O (nicht und teilweise getrocknet) und die Kinetik dieses Prozesses wurden mittels DTA, TG, DTG, IR, Röntgendiffraktometrie und chemischer Analyse von Mg und Cl untersucht. Die im Verlaufe der thermischen Analyse vor sich gehenden Reaktionen sind Dehydratisierung (in Schritten), thermische Hydrolyse von MgCl₂·H₂O und Chlorwasserstoffaustritt aus Magnesiumhydroxychloriden. Das Schmelzen der Phasen MgCl₂·6H₂O, MgCl₂·4H₂O und MgCl₂ ist in den thermischen Kurven ebenfalls zu erkennen. Im Luft- und Stickstoffstrom erfolgt ein Gewichtsverlust bis 800 °C, in statischer Luftatmosphäre dagegen nur bis 700 °C. MgO war in beiden Fällen Endprodukt der thermischen Behandlung. Die kinetischen Parameter der Reaktion (AktivierungsenergieE, präexponentieller FaktorA, scheinbare Reaktionsordnungb) wurden nach verschiedenen Methoden berechnet. Aktivierungsenergie und scheinbare Reaktionsordnung der Dehydratisierung nehmen mit abnehmendem Hydratationsgrad des Mg zu. Die Chlorwasserstoffabspaltung erfordert die höchste Aktivierungsenergie.

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, , , , ( ) . : ( ), . , . 800 °C, - 700 °C. B . , . , . .

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The authors express their appreciation to Dr. Jacob Nathan and Mr. Yoetz Deutch from th Geological Survey, Jerusalem, for the use of the thermal analysis instrument and for useful discussion, and to Mrs. Sarah Erlich from the same institute, for the chemical analysis. The financial support by Everyman's University, Tel-Aviv, and by the Hebrew University of Jerusalem is acknowledged.     

ESR studies of Ziegler type catalytic systems in the presence of CO

ESR studies of the interaction between Co(C₅H₇O₂)₂ and Al(C₂H₅)₃ in presence of CO reveal the formation of paramagnetic tri- and tetra-nuclear carbonyl compounds and the consecutive formation of complexes including one, two and three cobalt atoms. Al(C₂H₅)₃ decomposition is suggested to take place on the reduced transition metal to form Co–Al clusters. Structures for the paramagnetic heteronuclear clusters is proposed.

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

     

Catalytic performance in hydrodesulfurization of thiophene and ir investigation of Co and no adsorption over Co?Mo/Al2O3 and Ru?Co?Mo/Al2O3 catalysts

A new Ru–Co–Mo/Al₂O₃ catalyst has been prepared by impregnation of Ru salt as a secondary promoter onto Co–Mo/Al₂O₃ catalyst, and it was found that the Ru–Co–Mo/Al₂O₃ exhibited higher activity than Co–Mo/Al₂O₃ in hydrodesulfurization of thiophene to hydrocarbons. Ir studies on Ru–Co–Mo/Al₂O₃ revealed that the Co and NO adspecies increased significantly in intesnities and displayed a bathochromic shift in frequencies, as compared with Co–Mo/Al₂O₃.

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Ru–Co–Mo/Al₂O₃ Ru, , Co–Mo/Al₂O₃. Co–Mo/Al₂O₃. CO NO, Co Mo, Co–Mo/Al₂O₃. , Mo , Mo³⁺ Mo³⁺ Co Ru–Co–Mo/Al₂O₃.

     

Determination de la purete des substances chimiques par analyse calorimetrique differentielle (A. C. D.)

Purity determination by DSC is possible if the impurity concentration lies within the limits 0.01 to 20 mole%. The thermodynamic equation of Schröder-Van Laar was used.This equation takes into account the effect of the departure of solutions from ideality, and the difference between the heat capacities in the solid and molten states.

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Zusammenfassung Eine Reinheitbestimmung mittels DSC ist möglich, wenn die Konzentration der Verunreinigung zwischen 0.01 und 20 Mol-% liegt. Es wurde die thermodynamicshe Gleichung von Schröder-Van Laar angewandt. Diese Gleichung berücksichtigt den durch die Abweichung der Lösungen vom idealen Zustand bedingten Effekt und den Unterschied der Wärmekapazität im festen Zustand und in der Schmelze.

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, 0.01–20 %. --, .

     

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.

     

Development of phase composition for mixed Ni?Cu chromite catalysts. Interaction of initial substances

IR spectroscopic and kinetic studies of the interaction between basic carbonates of Cu and Ni and H₂CrO₄ allows to suppose that catalyst formation is affected by different structures of the initial substances. The formation of mixed Ni–Cu–Cr phases is observed during the step of chromate formation and is preserved after treatment by ammonium.

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Cu Ni H₂CrO₄. , . Ni–Cu–Cr- .

     

Promotion of the catalytic activity of zeolites by alkyl halides

The promotion of catalytic activity of zeolites by CCl₄ was studied in a pulse reactor using aromatic alkylation as model reaction. The reaction of surface OH groups with CCl₄ produced HCl which increased the catalytic activity. The maximum enhancement of activity occurred when the catalyst was weakly acidic.

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CCl₄ , . OH CCl₄ HCl, . , .

     

Acid-base and catalytic properties of binary oxides in the oxidative dehydrodimerization of toluene

Acidity and basicity of binary oxide catalysts measured by the CO₂ and NH₃ thermodesorption method are compared with their catalytic activity in oxidative conversion of toluene. The rate of toluene dehydrodimerization is shown to increase with the catalyst basicity.

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CO₂ NH₃ . , .

     

Selective hydrogenation of cyclopentadiene in the liquid phase on palladium catalysts

The catalytic hydrogenation of cyclopentadiene to cyclopentene was investigated under atmospheric pressure and 20°C in liquid phase with palladium carrier catalysts. The reaction was carried out in methanol and toluene in the presence of n-octylcatechol as a polymerization inhibitor. Using 0.56% Pd/Al₂ O₃, a 100% selectivity of the hydrogenation of cyclopentadiene to cyclopentene was achieved in toluene. In methanol, the selectivity of hydrogenation was lower and a partial polymerization of cyclopentadiene took place.

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20° C Pd- . -. 0,56% Pd/Al₂ O₃ 100%. , .

     

Structures of the borate complexes with a tetritol,pentitols and hexitols in solution. A calorimetric study

The molar heats for the reactions of borate with the polyhydroxy compounds pentaerythritol, L-arabinitol, xylitol, sorbitol and meso-inositol were determined by thermometric titrimetry. By means of the equilibrium constants, the corresponding Gibbs functions and entropies were also obtained. The results refer to aqueous medium at 25 °C and 0.1 M. The present data, together with previous data from this laboratory, lead to the conclusion that the differences in stability of these complexes are mainly determined by entropy, rather than by enthalpy factors. Unlike the other ligands (which are bidentate), pentaerythritol and meso-inositol seem to behave as tridentate ligands with borate. Nevertheless, their complexes exhibit very different stabilities, probably due to the different conformational freedoms of the two ligands in the uncomplexed form.

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Zusammenfassung Mittels thermometrischer Titration wurden die molaren Reaktionswärmen für die Reaktionen von Borat mit den Polyhydroxyverbindungen Pentaerythrit, L-Arabinit, Xylit, Sorbit und meso-Inosit bestimmt. Mittels der Gleichgewichtskonstanten erhielt man auch die entsprechenden Gibbsschen Funktionen und Entropien. Die Ergebnisse beziehen sich auf 25 °C undI=0,1 M. Auf Grund dieser und früherer Resultate der gleichen Autoren kann geschlußfolgert werden, daß die unterschiedliche Stabilität dieser Komplexe eher durch Entropieals durch Enthalpiefaktoren bestimmt wird. Im Gegensatz zu den anderen Liganden (die zweizählig sind) scheinen sich Pentaerythrit und meso-Inosit gegenüber Borat als dreizählige Liganden zu verhalten. Trotzdem zeigen ihre Komplexe eine sehr unterschiedliche Stabilität, wofür der Grund wahrscheinlich in dem unterschiedlichen Freiheitsgrad der zwei nicht im Komplex gebundenen Liganden liegt.

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, L- , , -. . 25° I=0,1 M. , , , , . , , - . , .

     

Kinetic conversion of complex hydrocarbon mixtures in reforming on platinum/alumina catalysts

General forms of the kinetic equations for the conversion of various hydrocarbons in reforming of multicomponent gasoline fractions on platinum/alumina catalysts have been confirmed experimentally by using a gradientless method.

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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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- , , .

     

Catalytic relevance of phase transformations accompanying the gas phase oxidation of ethanol on silica supported vanadia

Nonsteady state activity during the gas phase oxidation of ethanol in a simple flow reactor and its dependence on pretreatment and reaction conditions can be explained utilizing the previously presented model of possible surface vanadia phases on silica.

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.

     

Thiophene hydrodesulfurization on P?Mo, Si?Mo and Ti?Mo catalysts

Studies of the catalysts obtained by supporting P–Mo, Si–Mo and Ti–Mo heteropolyacids on anatase in thiophene hydrodesulfurization have revealed that the presence of HPA in the initial catalysts promotes the formation of the molybdenum state ensuring high reaction rates. A possibility for HPA synthesis when supporting paramolybdate on TiO₂, accounts for the great effect of the support on the properties of the catalyst.

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