Catalytic effect of an organic redox-indicator on the oscillatory behavior of 5-sulfosalicylic acid in acidic bromate

The presence of an organic redox indicator, sodium 4-diphenylamine-4-sulfonate, instead of inorganic catalysts has been found to greatly enhance the oscillatory behavior of 5-sulfosalicylic acid in acidic bromate under optinum conditions and slow stirring (50 rpm).

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-, 4--4- , , 5- , (50 ./).

     

Catalytic hydrogenation of nitrobenzene on solid sulfides and soluble rhenium thiocomplexes

Studies of the reduction of nitrobenzene in the catalytic hydrogenation on soluble rhenium thiocomplexes and solid ReS₂ and Re₂S₇ indicate that on homogeneous and heterogeneous rhenium sulfides it follows the same mechanism. Thiocomplexes are considered as possible analogs of the active sites in ReS₂ and Re₂S₇ sulfide catalysts.

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ReS₂ Re₂S₇. , . ReS₂ Re₂S₇.

     

Effect of acio properties of the alumina surface on the formation of chlorides during its interaction with CCl4

IR spectroscopy was employed to study acid properties of a series of alumina samples different in the phase composition and in the porous structure. The comparison of the surface acidity with the data on the quantitative formation of Cl^– during the interaction of CCl₄ with alumina indicates that the extent of chlorination of the samples tends to increase with increasing the surface acidity.

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- , . Cl^– CCl₄ , .

     

Competitive disproportionation and demethylation of toluene on Mg-containing Y zeolites

On Mg-containing Y zeolites toluene undergoes disproportionation and demethylation. The relative importance of the two processes is discussed.

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Mg- Y . .

     

Temperature and pressure oscillations during the autooxidation of benzaldehyde

The oscillatory behavior of the autooxidation of benzaldehyde catalyzed by cobalt(II) and bromide ions can be monitored besides potentiometry and/or spectrophotometry also by measuring the temperature of the reaction system and the pressure of oxygen above the solution as a function of time. The temperature and pressure oscillations can be explained only qualitatively so far.

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, , , / , . .

     

Quantitative DTA of epoxy adhesives of technological interest

The glass transition temperatures,T _g, and thermal effects of polymerization,H, have been determined for five epoxy adhesives of unknown composition. From the trendsH vs./t _cure it has been possible to attain a phenomenological kinetic order of the polymerization rate at 100° through an iterative calculation procedure. For most of the investigated adhesives there are reasons (double peak of polymerization and doubleT _g signal) to assume that they are graft copolymers.

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Zusammenfassung Die Glas-Übergangstemperaturen (T _g) und dieH thermische Effekte der Polymerisation wurden für fünf Epoxy-Klebstoffe unbekannter Zusammensetzung bestimmt.Aus den TrendsH gegenübert _cure war es möglich eine phenomenologische kinetische Ordnung der Polymerisationsgeschwindigkeit bei 100° durch ein iteratives Berechnungsverfahren zu ermitteln.Für die meisten untersuchten Klebstoffe besteht der Grund — Doppelpeak der Polymerisation und doppeltesT _g-Signal — sie als Pfropfcopolymere zu betrachten.

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Résumé On a déterminé, pour cinq adhésifs époxy de composition inconnue, les températures de transition vitreuseT _g et les effets thermiques de polymérisationH.A partir de la variation deH en fonction du temps de recuit et par une méthode de calcul itératif, un ordre cinétique phénoménologique de la vitesse de polymérisation à 100° a pu être obtenu.Pour la plupart des adhésifs étudiés l'existence d'un pic double de polymérisation et d'une double transition vitreuseT _g permet de supposer qu'il s'agit de copolymères greffés.

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T _g H. H.-t. 100° . T _g , - .

     

Thermal decomposition of calcium sulphate in carbon monoxide

Simultaneous TG and DTA studies were performed on analytical grade calcium sulfate and on samples of natural gypsum and phosphogypsum in carbon monoxide atmosphere. The decomposition temperatures and mechanism are influenced by the mineral impurities of the sample and the heating rate as well as the CO content of the gas atmosphere.

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Zusammenfassung Simultane TG- und DTA-Untersuchungen von analytisch reinem Calciumsulfat und Proben von natürlichem Gips und Phosphogips wurden in Kohlenmonoxidatmosphäre ausgeführt. Temperatur und Mechanismus der Zersetzung werden durch mineralische Verunreinigungen der Probe, durch die Aufheizgeschwindigkeit und durch den CO-Gehalt der Gasatmosphäre beeinflußt.

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. - , , .

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The authors are indebted to Professor M. Veiderma for fruitful discussions and continuous support. The scholarship from Finnish Government to one of us (R. K.) is gratefully acknowledged.     

Kinetics and mechanism of the decomposition of pyrite under conventional and quasi-isothermal — quasi-isobaric thermoanalytical conditions

The kinetics and mechanism of the thermal decomposition of pyrite were examined by the method of quasi-isothermal and quasi-isobaric thermogravimetry (Q-TG). It emerged that by means of this technique the overlapping partial processes of the complicated oxidation and decomposition reactions of pyrite can be separated and studied independently from one another. It was found that the partial reactions FeS₂=FeS +S and Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ are endothermic processes taking place quasiisothermally and leading to equilibrium, while the oxidation FeS+O₂=Fe₂O_3–x(SO₄)_x is an exothermic process which takes place in an oscillating manner in a rather broad temperature interval.

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Zusammenfassung Autoren untersuchten die Kinetik und den Mechanismus der thermischen Zersetzung von Pyrit durch quasi-isotherme und quasi-isobare Thermogravimetrie (Q-TG). Es stellte sich heraus, daß sich überlagernde Teilprozesse der komplizierten Oxydations- und Zersetzungsprozesse von Pyrit mit Hilfe dieser Technik absondern und unabhängig voneinander untersuchen lassen. Es wurde festgestellt, daß die Teilreaktionen FeS₂=FeS+S und Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ endotherme Prozesse sind, die quasi-isotherm verlaufen und zu einem Gleichgewicht führen, während die Oxydation FeS+O₂=Fe₂O_3–x(SO₄)_x ein exothermer Prozeß ist, der oszillierend in einem ziemlich breiten Temperaturintervall verläuft.

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(Q-) . . , FeS₂=FeS+S Fe₂O_3–x(S₂O₄)_x=Fe₂O₃+SO₃ , . FeS+O₂ =Fe₂O_3–x(SO₄)_x , .

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The authors thank Prof. E. Pungor for valuable discussions, and Mrs. M. Kiss and Miss I. Fabian for their technical assistance.     

Co-adsorption studies of ethene with isotopically labelled water and hydrogen on copper/silica

The coadsorption of ethene with isotopically labelled water and hydrogen has been studied at temperatures between 423 and 623 K in a flow system. Ethene exchange has been shown to be independent of hydrogenation. When water is presnet, hydrogenation is poisoned but exchange can occur.

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423–623 . . , .

     

The importance of the CO 2 2− anion in the mechanism of thermal decomposition of oxalates

The effects of active (carbon dioxide and carbon monoxide) and neutral (helium, argon and nitrogen) atmospheres on the course of thermal decomposition of oxalates have been studied and compared. A mechanism of thermal decomposition has been proposed on the basis of the results obtained, the first stage of which consists in a heterolytic dissociation of the C-C bond, with the formation of carbon dioxide and the CO ₂ ^2– anion.

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Zusammenfassung Die Effekte von aktiven (Kohlendioxid und Kohlenmonoxid) und neutralen (Helium, Argon, Stickstoff) Atmosphären auf den Verlauf der thermischen Zersetzung von oxalaten wurden untersucht und miteinander verglichen. Aus den erhaltenen Ergebnissen wird ein Mechanismus der thermischen Zersetzung abgeleitet, dessen erster Schritt die heterolytische Dissoziation der C-C-Bindung unter Bildung von CO₂ und des CO ₂ ^2– -Anions ist.

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(- ) (, ) . , C-C CO ₂ ^2– .

     

A Thermal study of the precipitates formed in ammonia neutralization of acidic solutions of dissolved phlogopite

The precipitates containing mainly iron, aluminium and magnesium hydroxides, obtained from phlogopite dissolved in nitric acid by means of the neutralization procedure with ammonia, have been investigated by thermal analysis (TG, DTG and DTA). According to the present study, which is part of a larger investigation into the chemical utilization of Finnish mica minerals, the formation of solid solutions between iron and aluminium hydroxides in silt increases with an increasing neutralization temperature. Nitrogen exists mainly in the form of nitrate in silts, and magnesium forms mixed hydroxides with aluminium, which causes a separation between the iron hydroxide and magnesium aluminium hydroxide phases.

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Zusammenfassung Die von in Salpetersäure gelöstem Phlogopit durch Neutralisierung mit Ammoniak erhaltenen, hauptsächlich Eisen-, Aluminium- und Magnesiumhydroxid enthaltenden Niederschläge wurden thermoanalytisch (TG, DTG und DTA) untersucht. In der vorliegenden Arbeit, die Teil einer grossangelegten Untersuchung zur chemischen Nutzung finnischer Glimmermineralien ist, wird gezeigt, dass die Bildung fester Lösungen von Eisen- und Aluminiumhydroxiden in Schluff mit zunehmender Neutralisationstemperatur ansteigt. Stickstoff kommt in Schluff hauptsächlich in Form von Nitraten vor, und Magnesium bildet Mischhydroxide mit Aluminium, was eine Trennung der Eisenhydroxidphase von der Magnesium-Aluminium-Hydroxidphase bewirkt.

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, , , . . , , . , , , , .

     

Studies on catalytically active surface compounds, IX. Formation of O2? radicals on VCl4/SiO2 catalysts

The conditions for the formation of O ₂ ^– on VCl₄/SiO₂ catalysts have been investigated. It is shown that thermal vacuum treatment (TVT) of unhydrolyzed catalysts leads to partial hydrolysis of the surface vanadium complex caused by the silanol groups of the support. The ability of the catalysts to generate O ₂ ^– radicals was found to depend on the degree of hydrolysis caused by thermal vacuum treatment.

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O ₂ ^– VCl₄/SiO₂. , , . , O ₂ ^– , .

     

Effect of dentate number of anchored phosphine ligands on the composition and catalytic properties of their palladium complexes

Mono-, di- and triphosphine ligands anchored by a Si–C bond to the surface of silica have been synthesized. Complexes of Pd(II) and Pd(O) with these ligands have been obtained. On the basis of elemental analysis and UV spectroscopy, structures of the complexes formed are suggested. The catalytic properties of the above complexes in the selective hydrogenation of cyclopentadiene are compared.

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-, - , Si–C . Pd(II) Pd(O) . - . .

     

The activity of Ni/AlPO4, Ni/AlPO4?Al2O3 and Ni/AlPO4?SiO2 catalysts in the hydrogenation of e-cinnamaldehyde

Liquid-phase catalytic hydrogenatio of E-cinnamaldehyde was carried out by using new supported nickel catalysts (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ and Ni/AlPO₄–SiO₂) in methanol as solvent under low hydrogen pressure (4.1 bar) and 298 K. The kinetic orders are zero in H₂ and aldehyde. The selectivity to the hydrogenaton of the C=C double bond is very high (>99%)

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- (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ Ni/AlPO₄–SiO₂) (4,1 ) 298 . H₂ . C–C (>90%).

     

Reactivity of coordinated O2? ion-radicals in the oxidation of organic compounds

By the flow ESR method, the rates of the reaction of the radical complex Ti(IV)(O ₂ ^– ) with some aromatic compounds in aqueous solution have been measured. An elementary step of these reactions seems to be one-electron oxidation with the formation of a substrate cation-radical.

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- Ti(IV)(O ₂ ^– ) . - -.

     

On the calculation of activation energies using a modified Kissinger method

Augis and Bennett (J. Thermal Anal. 13 (1978) 283.) [6] recently proposed a modified Kissinger method for determining the activation energy of a transformation. It is shown that the proposed method was, in fact, based upon a modification to the equation for the rate of reaction under non-isothermal conditions. The apparent discrepancy between the proposed method and the original Kissinger method is therefore resolved. The modified rate equation appears to have, at best, only a limited application. However, if the equation should be appropriate for a particular transformation, it is demonstrated that Augis and Bennett's method would be the correct method for determining the activation energy.

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Zusammenfassung Von Augis und Bennett (J. Thermal Anal.13, (1978) 283) wurde eine modifizierte Kissinger-Methode zur Bestimmung der Aktivierungsenergie einer Umwandlung vorgeschlagen. Es wird gezeigt, dass die vorgeschlagene Methode tatsächlich in einer Modifizierung der Gleichung für die Reaktionsgeschwindigkeit unter nicht-isothermen Bedingungen ihren Ursprung hat. Die scheinbare Diskrepanz zwischen der vorgeschlagenen Methode und der ursprünglichen Kissinger-Methode wird dadurch behoben. Die modifizierte Geschwindigkeitsgleichung hat bestenfalls nur eine begrenzte Anwendung. Jedoch, bei Eignung dieser Gleichung für eine bestimmte Umwandlung zeigt sich, dass die Methode von Augis und Bennett die richtige Methode zur Bestimmung der Aktivierungsenergie sein kann.

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(J. Thermal Anal. 13 (1978) 283.) - . , , , . , . , , , . , , .

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The author is indebted to the Senate of the University of Queensland for the award of a University Research Fellowship; and to Professor R. R. Stephens for providing laboratory facilities.     

Li/MgO catalysts: II. A DTA and TG study of precursors

The thermal decomposition of precursors of Li/MgO catalysts prepared from different Mg and Li compounds is reported. Dehydration and dehydroxylation is observed in both cases, in addition to decomposition of LiNO₃, but not of Li₂CO₃. The properties of the solids are related to the melting and spreading of LiNO₃ or Li₂CO₃ before or after Mg(OH)₂ dehydroxylation.

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Li/MgO, Mg Li. LiNO₃, Li₂CO₃, . LiNO₃ Li₂CO₃ Mg(OH)₂.

     

Thermal behaviour of transition metal complexes of dithiocarbazic esters. II

A thermal study (simultaneous TG and DTA measurements) was carried out on the dithiocarbazic ester complexes M[N³CH₂R₁N²C¹(S)SCH₃]₂, where M=Ni, Pt; R₁=C₆H₅. The following disproportionation reaction occurs in the solid state: II is formed through deprotonation of the CH₂ group bound to N³, whereas III is formed through protonation of N³.The influence of inductive and/or steric effects on the mechanism of this reaction is discussed, taking into account the electrochemical and X-ray data on the complexes Pt[NRNC(S)SR']₂ with differentR substituents: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃; R=CH₃, CH₂Ph.These results accord with the behaviour of the same complexes in solution.

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Zusammenfassung Dithiokarbamidsäureesterkomplexe M[N³CH₂R₁N²C¹(S)SCH₃]₂ mit M=Ni, Pt und R₁=C₆H₅ wurden thermisch untersucht. Im festen Zustand spielt sich folgende Disproportionierungsreaktion ab: II wird durch Deprotonierung der an N³ gebundenen CH₂ Gruppe und III durch Protonierung des Atoms N² gebildet. Unter Zuhilfenahme der elektrochemischen und Röntgendaten der Komplexe Pt[NRNC(S)SR']₂ mit verschiedenen Substituenten R: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃ und R=CH₃ bzw. CH₂Ph wurde der Einfluß von induktiven und/or sterischen Effekten auf den Reaktionsmechanismus diskutiert. Diese Ergebnisse stehen in Übereinstimmung mit dem Verhalten der Komplexe in Lösung.

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M[N³CH₂R₁N²C¹(S)SCH₃]₂, M= Ni, Pt,R ₁=C₆H₅. : II CH₂ , N³, III N². () , Pt[NRNC(S)SR]₂, R= , aR= . .

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We thank prof. A. La Ginestra for many helpful discussions on the various aspects of this work.     

Investigations on the compatibility of milk fat fractions and lauric fats

The compatibility of a lauric fat with several milk fat fractions (MF) was investigated. The enthalpy of crystallization was measured by differential scanning calorimetry (DSC). These values were related to the corresponding values calculated for an Ideal Blend. The different compatibility of the milk fat fractions with the lauric fat could be shown by this method very clearly.

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Untersuchungen zur Mischbarkeit/Verträglichkeit von Milchfettfraktionen mit laurischen Fetten

Zusammenfassung Die Mischbarkeit/Verträglichkeit von Milchfettfraktionen mit einem laurischen Fett wurde differenzkalorimetrisch untersucht. Die Auswertung der Befunde bezieht sich auf die entsprechenden Rechnungswerte einer Idealen Mischung. Es wurde nachgewiesen, da sich diese Milchfette deutlich in ihrer Mischbarkeit unterscheiden.

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. $ . , $ - . $ .

     

Effect of molybdenum catalysis on the perborate-bromide reaction. Kinetics and mechanism and some theoretical considerations

In the presence of molybdenum, both the uncatalyzed and the catalyzed reactions proceed simultaneously. An equation for k_cat was derived and the effect of temperature was described through a temperature function F(T) by the use of the Arrhenius-Eyring equation. A plausible mechanism is postulated and the theoretical background given for the analytical application of molybdenum.

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. k_cat, -. .