Kinetic parameters of thermal decomposition of complex of β-cyclodextrin with water

The apparent kinetic parameters of the thermal decomposition of the-cyclodextrin-water complex were estimated from thermogravimetric data. Various calculation methods were used and the results compared. All methods except the Kissinger method gave a reaction order near to zero and an activation energy in the range 60 to 65 kJ/mol. Some trials were made to extrapolate the activation energy values to semi-isothermal conditions (65.7 kJ/mol). The loss in weight indicated the presence of 11 water molecules in the complex. This was liberated in single stage, despite its occurrence as two distinct types, as shown by crystallographic studies.

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Zusammenfassung Auf Grundlage von thermogravimetrischen Daten wurden die scheinbaren kinetischen Parameter des Thermozerfalles von-Cyclodextrin-Wasser- Komplexen geschätzt. Die durch verschiedene Rechenmethoden erhaltenen Ergebnisse wurden in Tabelle 3 verglichen. Mit Ausnahme der Kissinger-Methode ergaben alle Verfahren eine Reaktionsordnung von annähernd Null und eine Aktivierungsenergie im Bereich 60–65 kJ/mol. Ausserdem wurde versucht, die Aktivierungsenergiewerte auf halbisotherme Bedingungen zu extrapolieren (65.7 kJ/mol). Der Masseverlust weist elf Wassermoleküle im Komplex nach, die in einem einzigen Schritt abgegeben werden, ungeachtet dessen, dass kristallographische Untersuchungen die Wassermoleküle zwei verschiedenen Typen zuordnen.

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-- . , . , , — 60–65 · ^–1. (65,7 · ^–1). , , , , .

     

Study of the heterogeneous decomposition of tertiary-butyl alcohol and di-tertiary-butyl peroxide on SiO2 by temperature programmed desorption

In the study of the interaction of tertiary-butyl alcohol and di-tertiary-butyl peroxide with SiO₂ treated with KCl by means of temperature programmed desorption, pulsation desorption (oscilatory behavior) is observed.

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- - SiO₂, KCl - , ( ).

     

Phase coexistence and complicated dynamics in open catalytic systems

The simplest catalytic system with surface phase transitions in CSTR has been studied. It is shown that the possible number of steady states is directly determined by that of phase coexistence regions on the phase diagram of the adsorption layer.

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. , , .

     

Variations in the cooling transitions of potassium nitrate

Because of questions concerning the suitability of potassium nitrate as a dynamic temperature standard for DTA, the relation between the experimental procedure and the resulting curves was ascertained for the Standard Reference Material KNO₃. The material behaves differentlyon cooling in open pans than in cylindrical holders because confinement in the latter case initiates reversion to the room temperature form. Under the conditions of use as a dynamic temperature reference material, the curves are accurately reproducible.

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Zusammenfassung Zur Überprüfung der Eignung von Kaliumnitrat als dynamische Temperatur-Eichsubstanz für die DTA, wurde der Zusammenhang des Versuchsvorganges und der erhaltenen Kurven für das Standard-Referenz-Material KNO₃ untersucht. Die Substanz verhält sich bei der Kühlung in offenen Tiegeln und in zylindrischen Behältern unterschiedlich, da in letzteren die Begrenztheit die Reversion zur Zimmertemperatur-Form in Gang setzt. Unter den für das dynamische Temperatur-Referenz-Material gegebenen Bedingungen sind die Kurven gut reproduzierbar.

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Résumé En raison de l'emploi du nitrate de potassium comme étalon de température en ATD, on a étudié l'influence des conditions d'expérience sur les courbes obtenues. Le comportement de ce corps est différent si on effectue le refroidissement dans des capsules ouvertes ou dans des creusets cylindriques. Dans ce dernier cas, le manque d'espace initie le retour à la forme stable delà température ambiante. Dans les conditions d'emploi comme matériau de température étalon, les courbes sont exactement reproductibles.

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. - , , .

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One of us is indebted to the U. S. National Science Foundation for support of part of this study.     

Catalytic cracking and dehydrogenation of butanes and neopentane on reduced copper-exchanged Y-zeolites

The activity and selectivity of reduced Cu–Y zeolites containing acidic sites either only of Brönsted or only of Lewis type suggest that the Lewis acid sites are active in the cracking of butanes and neopentane, while both Lewis acid and Lewis base sites are involved in the mechanism of the dehydrogenation of these reactants.

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Cu–Y , , , , . , .

     

Kinetics of hydroperoxyde-dependent naphthalene hydroxylation involving cytochrome P-450 of the intact and induced enzyme systems of rat liver microsomes

Hydroperoxide-dependent naphthalene hydroxylation involving rat liver microsomes has been studied. The direct interaction between cytochrome p-450 and cumyl hydroperoxide (CHP) has been demonstrated. K_m values with respect to both the substrate and CHP have been determined using intact and induced enzyme systems. The nature of the hydroxylating agent and the possible role of high-valence iron in the processes of hydroxylation by microsomal systems is discussed.

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. P-450 . K_m . , .

     

Influence of silica on the properties of evaporated V?Mo oxide catalysts

According to⁵¹V-NMR studies of the state of vanadium ions in parent solutions and in catalysts, evaporated V–Mo oxide catalysts are shown to be more active and selective in acrolein oxidation to acrylic acid than unsupported samples.

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- , , , . e₁V .

     

Catalytic ethoxylation of phenol and phenol derivatives

The kinetics of catalytic mono- and polyethoxylation of phenol, p-cumyl-phenol and p-isooctylphenol have been studied in the presence of strongly basic anion exchanger Wofatit SBW in hydroxy form. The influence of substituents on the rate has been investigated and the mechanism of the reaction is discussed.

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- , - Wofqtit SBW . .

     

Structure and reactivity of vanadium(V) complexes formed in the reaction between vanadyl acetylacetonate and alkyl hydroperoxides. To the mechanism of selective epoxidation of olefins

Vanadium(V) complexes formed in the reaction between vanadyl acetylacetonate and alkylhydroperoxides are characterized according to their¹H and⁵¹V NMR spectra and the reactivity of these complexes towards cyclohexene is studied.

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¹H ⁵¹V , .

     

Microcalorimetric investigation of the recrystallization behaviour of polycrystalline copper deformed at room-temperature

The recrystallization of 5 N copper samples which had been deformed at roomtemperature by torsion to an average shear of by rolling to 65% r.c.s. was investigated by means of a commercial heatflow calorimeter.During recrystallization, which was also studied by hardness tests and optical microscopy, a stored energy release of the order of 0.145 cal/g was observed. Some problems inherent in the use of microsamples are discussed. By kinetic analysis, based on variation of the linear heating rate, a value of 21.9 kcal mole^–1 was determined for the apparent activation energy of the recrystallization process in torsion samples.

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Zusammenfassung Die Rekristallisation von 5 N Kupferproben, die bei Raumtemperatur durch Torsion bzw. durch Walzen (65%) verformt worden waren, wurde mit einem kommerziellen Wärmeströmungskalorimeter untersucht. Bei der Rekristallisation, die ebenfalls mit Härtemessungen und Gefügeuntersuchungen verfolgt wurde, wird eine Energiefreigabe von etwa 0.145 cal/g beobachtet. Einige bei der Verwendung von Microproben auftretende Probleme werden diskutiert. Eine Analyse der Kinetik, die auf der Variation der linearen Aufheizgeschwindigkeit basiert, ergab für die scheinbare Aktivierungsenergie des Rekristallisationprozesses in Torsionsproben einen Wert von 21.9 Kcal Mol^–1.

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Résumé On a étudié à l'aide d'un calorimètre à flux de chaleur commercial la recristallisation d'échantillons de cuivre 5 N, préalablement déformés à température ambiante par torsion ou par laminage (65%).Lors de la recristallisation, également suivie par mesures de dureté et examens de structure, on observe un dégagement d'énergie d'environ 0,145 cal/g. Les problèmes qui surgissent lors de l'utilisation de prélèvements micro sont discutés. L'énergie d'activation apparente du processus de recristallisation après l'écrouissage par torsion s'élève à 21.9 kcal mol^–1.

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5H , , , 65% . . . , , 0.145 /. , . , , , 21.9 ^–1.

     

Hydrogen adsorption on chromia-supported iridium catalyst

Effect of thermal pretreatment of chromia-supported iridium catalyst on hydrogen adsorption was studied. It was found that the hydrogen uptake by Ir/Cr₂O₃ was highly dependent on the reduction temperature. The catalyst proved to be resistant to sintering in oxygen atmosphere at temperatures up to 700 °C and it showed symptoms of redispersion even at 650 °C.

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. Ir/Cr₂O₃ . 700°C, , 650°C .

     

Violation of steady state process in CO hydrogenation to alcohols

Studies of the effect of iron supported on the surface of a K₂CO₃-doped zinc-chromium catalyst or entrapped from synthesis gas, have revealed violation of the steady state process in alcohol synthesis. Periodic oscillations in temperature and concentrations of reactants and reaction products are observed.

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, K₂CO₃ - -, , , , .

     

Mechanism of catalysis and factors responsible for oxide catalyst activity in deep oxidation reactions

A general scheme for the deep oxidation mechanism on oxide catalysts including stepwise and concerted mechanisms as well as their mutual transformations is suggested. The principal factor responsible for the activity in the concerted mechanism region is the rate of oxygen binding. For the stepwise mechanism the main factor is the rate of catalyst interaction with oxidizable reactant.

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, . , . .

     

Capacite calorifique molaire du compose Sb·405Te·595 dans les etats solides et liquides entre 298 K et 922 K

Heat capacity (C _p ) of the compound Sb_·405Te_·595 in solid and liquid states at constant pressure are calculated from the results of experimental drop calorimetric method. The heat of fusion of the compound is deduced. A phase transition in the solid state has been put in evidence.

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Zusammenfassung Basierend auf Ergebnissen einer Dropkalorimetrie-Methode wurde die Wärmekapazität für konstanten Druck (C _p ) der Verbindung Sb_·405Te_·595 für den festen und flüssigen Aggregatzustand errechnet und die Schmelzwärme der Verbindung abgeleitet. Ein Phasenübergang im festen Zustand wurde vorausgesetzt.

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, , (C _p ) Sb_0.405Te_0.595 , . .

     

Catalytic activity of high-silicon TsVK and Y type zeolites

Conversion of paraffins on TsVK and Y zeolites follow a similar mechanism yielding the same intermediates. Low selectivity of Y zeolites with respect to aromatic hydrocarbons is attributed to the strong adsorption of these hydrocarbons on zeolites. It is assumed that the centers of strong adsorption are Al³⁺ ions in cationic positions in zeolite.

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, . . , Al³⁺ .

     

Kinetic studies of multi-step thermal degradations of copolymers or polymer mixtures

A kinetic analysis of multi-step thermogravimetric curves was developed for separation of overlapping decomposition steps to determine their individual reaction order, activation energy and weight loss. The method was applied in three instances: (a) separation of evaporation from decomposition for an isobutene-butadiene copolymer; (b) effects of drying conditions on the volatile content of a styrene-indene resin; (c) separation of dehydrochlorination from cyclodecomposition of poly(vinyl chloride).

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Zusammenfassung Eine kinetische Analyse von mehrstufigen thermogravimetrischen Kurven wurde entwickelt, um überlappende Zersetzungsstufen zu trennen, ihre individuellen Reaktionsordnungen, Aktivierungsenergien und Gewichtsverluste zu bestimmen. Die Methode wurde in drei Fällen eingesetzt: (a) Trennung der Verdampfung des Isobuten-Butadien-Kopolymers von der Zersetzung; (b) die Wirkung der Trocknungsbedingungen auf den Gehalt an flüchtigen Substanzen eines Styrol-Inden-Harzes; (c) Trennung der Dehydrochlorierung des Poly-Vinylchlorids von der Ringspaltung.

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Résumé On a mis au point une méthode d'analyse cinétique des courbes thermogravimétriques en plusieurs termes pour séparer les étapes de décomposition qui se chevauchent et déterminer pour chacune d'elles l'ordre de réaction, l'énergie d'activation et la perte de poids. On a utilisé cette méthode dans trois cas: a) pour distinguer l'évaporation de la décomposition du copolymère isobutène-butadiène, b) pour étudier l'influence des conditions de séchage sur la teneur en substances volatiles d'une résine styrène-indène, c) pour distinguer la déchlorhydratation du chlorure de polyvinyle de la décomposition du cycle.

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, , . : () -; () - ; () .

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Paper presented at the International Symposium on Macromolecular Chemistry, Budapest, 1969.     

Calculation of the energy spectrum of surface oxygen on CuO by the interacting bonds method

Using the interacting bonds model a calculation has been made for the energy spectrum of oxygen on the CuO surface. Dissociative adsorption of oxygen can be realized in one and two-center forms with 9.2 and 60.4 kcal/mol, respectively. Intermediate values of the adsorption heats are attributed to oxygen adsorption on induced and biographic defects. The theoretically calculated energy spectrum of adsorbed oxygen is in reasonable agreement with that obtained experimentally from the dependence of isosteric heats of oxygen adsorption on the surface coverage.

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CuO. - 9,2 60,4 / . . .

     

Comparative analysis of purity determination methods using a differential scanning calorimeter

Comparative analysis of several methods for purity determination using DSC is presented. This is based on a mathematical model including the construction of theoretical melting curves for two-component systems and the calculation of recorded melting curves with the help of a set of equations describing the formation of a DSC output signal. It is shown that the true accuracy of purity determinations in the range of impurity concentrations ¯x=0.005–0.02 does not exceed 30–50%.

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Zusammenfassung Eine Vergleichende Analyse verschiedener Methoden zur Reinheitsbestimmung mittels DSC wurde ausgeführt. Diese basiert auf einem mathematischen System, daß die Konstruktion theoretischer Schmelzkurven für Zweikomponentensysteme und die Berechnung von registrierten Schmelzkurven mit Hilfe einer Reihe die Ausbildung des DSC-Signals beschreibenden Gleichungen in sich einschließt. Es wird gezeigt, daß die Genauigkeit der Reinheitsbestimmungen bei Konzentrationen der Verunreinigungen von ¯X₂=0.005–0.02 30–50% nicht überschreitet.

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, , . , 0,005-0,02 30–50%.

     

Correlation between acid strength (Ho) and ammonia desorption temperature for aluminas and silica-aluminas

Correlation between the temperature at which a base is desorbed and the acid strength (H_o) of the sites set free by it, was looked for. Ammonia was employed as base. A linear correlation of the type H_o=+/T (K) is valid with and constants, dependent on the adsorbate and the adsorbent.

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(H_o) , . H_o=+/T (K), .