The thermal decomposition reactions of bis-(pyridine-2-aldoxime)-copper(II) complexes

The thermal properties of some complexes of copper(II) with pyridine-2-aldoxime (HPAO), where the ligand appears either as the ion (PAO^–) or as a neutral molecule, were determined in vacuo and in dynamic nitrogen and oxygen gas atmospheres. The study was carried out by thermoanalytical (TG, DTG. DTA), spectroscopic and spectrometric (UV-visible, IR, diffuse reflectance, mass) techniques.The initial decomposition temperature is influenced by the number of acid hydrogens in the complex; the thermal stability sequence in vacuo is: [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]The thermal decomposition reactions occur in several separate steps, the first of which gives rise to partial ligand decomposition, the reduction of copper(II) to copper(I), and the conversion of the residual pyridine-2-aldoxime into acid amide.

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Zusammenfassung Die thermischen Eigenschaften einiger Komplexe von Kupfer(II) mit Pyridin-2-aldoxim (HPAO), in denen der Ligand entweder als Ion (PAO^–) oder als neutrales Molekül vorliegt, wurden im Vakuum und in dynamischer N₂- und O₂-Atmosphäre ermittelt. Zur Untersuchung wurden thermoanalytische (TG, DTG, DTA) und spektrometrische (UV-sichtbar, IR, diffuse Reflektionsspektrophotometrie, Massenspektrometrie) Techniken herangezogen. Die Temperatur, bei der die Zersetzung beginnt, wird durch die Zahl der sauren Wasserstoffatome im Komplex beeinflußt; für die thermische Stabilität im Vakuum gilt die Reihenfolge [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]. Die thermischen Zersetzurigsreaktionen verlaufen in mehreren diskreten Schritten, wobei der erste von diesen eine partielle Zersetzung des Liganden, die Reduktion von Kupfer(II) zu Kupfer(I) und die Konversion des verbleibenden Pyridin-2-aldoxims in das Säureamid in sich einschließt.

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-2- ( ), (-), . (, , ) , - , , - . , [Cu(PAO)₂H]CI > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂] , , -2- .

     

IR spectra of oxygen adsorbed on SnO2

IR spectra of oxygen adsorbed on SnO₂ with and without lattice defects have been studied. At low temperatures oxygen is adsorbed on defect SnO₂ in two forms of O ₂ ^– . This supports the earlier results obtained by ESR. The low-temperature forms of adsorbed oxygen (unrevealed in ESR spectra) were detected on defectless SnO₂. High-temperature forms of adsorbed oxygen appear in the IR-spectra as bands due to vibrations of the cation-oxygen bond.

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- SnO₂. , O ₂ ^– , . SnO₂ .

     

Determination of the surface acidity of solid catalysts

A novel method has been developed for determining the surface acidity of white, as well as deeply colored porous solids. The method, which was tested on Al₂O₃, SiO₂–MgO–Al₂O₃ and Fe₂O₃ catalysts, is based on the adsorption of pyridine or benzylamine on acidic sites and subsequent displacement of the adsorbed bases by n-butylamine. A linear correlation was found between the concentration of acidic sites on Al₂O₃ and Fe₂O₃ catalysts and their activity in the dehydration oftert-butyl alcohol.

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, . , Al₂O₃, SiO₂–MgO–Al₂O₃ Fe₂O₃, -. Al₂O₃ Fe₂O₃ - .

     

Kinetic and mechanistic studies on the oxidation of sulfanilic acid by peroxomonophosphoric acid

Oxidation of sulfanilic acid to the corresponding azoxy derivative by peroxomonophosphoric acid (PMPA) has been studied in aqueous medium. The observed bell-shaped pH-rate profile has been rationalized on the basis of protonation of the amino group and ionization into different PMPA species and a suitable rate law has been proposed. The mechanism of oxidation involves the nucleophilic attack of nitrogen on the electrophilic peroxo oxygen.

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- (PMPA) . pH— , PMPA . .

     

Effects of admixtures of potassium bromide on the thermal decomposition of potassium bromate

The effects of admixtures of potassium bromide (2.5% and 5%) on the thermal decomposition of potassium bromate were studied within the temperature range 653–683 K. The fraction decomposed() vs. time (t) relations revealed (i) initial gas evolution, (ii) acceleratory and (iii) decay steps. The data were analysed on the basis of the first-order law with two rate constantsk ₁ andk ₂,k ₁ being the rate constant for the initial, slow first-order process (0.02, 0.26), andk ₂ being the rate constant for the subsequent faster process, holding within the range 0.21 to 0.98. Upon increase of the concentration of added potassium bromide to 5%, the range for the slow and faster processes became 0.01 to 0.16 and 0.1 to 0.98, respectively. At a given temperature,k ₁ increased with increasing bromide concentration, whereask ₂ almost identical for pure potassium bromate and its mixtures (2.5% and 5% bromide).

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Zusammenfassung Im Temperaturbereich von 653–683 K wurde der Einfluß von Beimengen von Kaliumbromid (2,5% und 5%) auf die thermische Zersetzung von Kaliumbromat untersucht. Die Funktion der zersetzten Menge () in Abhängigkeit von der Zeit (t) weist eine anfängliche Gasentwicklung(i), eine beschleunigte(ii) und eine abklingende Stufe(iii) auf. Die Daten wurden auf der Grundlage einer Kinetik erster Ordnung mit den zwei Geschwindigkeitskonstantenk ₁ undk ₂ durchgeführt, wobeik ₁ die Geschwindigkeitskonstante für den einleitenden, langsameren Schritt erster Ordnung ist (0,02, 0,26) undk ₂ die Geschwindigkeitskonstante für den darauffolgenden schnelleren Vorgang mit Werten zwischen 0,21 und 0,98. Bei Erhöhung der Konzentration von Kaliumbromid auf 5% betrug der Bereich für den langsameren und den schnelleren Vorgang 0,01 bis 0,16 bzw. 0,10 bis 0,98. Bei gegebener Temperatur steigtk ₁ mit zunehmender Kaliumbromidkonzentration an, währendk ₂ für reines Kaliumbromat und seine Mischungen mit 2,5% und 5% Kaliumbromid fast identisch bleibt.

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653–683 (2,5 5%) . , . k ₁ k ₂, ( 0,02 0,26), - 0,21–0,98. 5% k ₁ k ₂ , , 0,01–0,16 0,1–0,98. k ₁, , k ₂ , (2,5 5%) .

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The work is dedicated to the memory of the late Prof. S. R. Mohanty.     

Acetylene adsorption on a clean iridium surface

The interaction of C₂H₂ with a polycrystalline iridium surface at 140 KT500 K has been studied by AES, XPS and UPS. A model of the bonding between C₂H₂ and Ir by the 1 orbitals of the hydrocarbon is proposed. The more pronounced energy splitting between the orbitals of acetylene during adsorption compared to that in the gas phase is ascribed to deformation of the acetylene molecule.

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C₂H₂ . 140 KT500 K AES, XPS UPS. C₂H₂ Ir 1- . - , , .

     

Interaction of PM12?nVnO40?(3+n) (M=Mo, W) heteropoly complexes with nitrogen oxide

In aqueous solution, PM_12–nV_nO₄₀ ^–(3+n) (M=Mo,W) hetero-polyanions provide a much faster oxidation of NO than mononuclear VO ₂ ⁺ ions, yielding HNO₂, NO ₃ ^– and reduced HPA.

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, PM_12–nV_nO₄₀ ^–(3+n) (M=Mo,W) , VO ₂ ⁺ , NO HNO₂ NO ₃ ^– .

     

Kinetics of thermal decomposition of diacyl peroxides in the presence of aerosil

In the presence of aerosil the thermal decomposition of the polymeric peroxide of sebacic acid is enhanced proportionally to the filler weight fraction in the reaction system. This is attributed to the interaction of peroxide groups with acidic groups on the aerosil surface and their decomposition according to a nonradical mechanism unlike the homolytic radical decomposition in solution.

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, , . .

     

Estimation of nonlinear relaxation of catalytic reactions

Nonlinear relaxation time has been considered as a differential characteristic determined by the reciprocal value of the relative decrease in the deviation rate of the current concentration vector of intermediates from that of their steady-state concentrations. This characteristic is used for the analysis of some model reactions.

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, , .

     

Infrared study of the interaction of nitric oxide with CuY zeolites

Infrared studies of the interaction of NO with CuY–A zelites have been made over the temperature range from –100°C to 400°C. Several forms of NO adsorption have been found, in particular, a stable cis-dimer at low temperatures.

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- (–100+400°C) NO CuY–A . NO, ë - .

     

Design of a gas chromatograph for chemical kinetic studies and measurement of other physicochemical properties

A simple gas chromatograph was constructed for the purpose of studying reaction kinetics parameters and physicochemical properties. The instrument has a large oven that can accommodate rather long and straight columns; an efficient air circulation makes the temperature gradients inside the oven negligible. The injector has a small dead volume and a thermal conductivity detector was used.

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- . , . , . .

     

Effect of hydrogen pressure on the selectivity of 2-butene-1-al hydrogenation

The effect of hydrogen pressure on the selectivity of hydrogenation of 2-butene-1-al at the carbonyl group in the presence of Ru and Ru–ZnO catalysts indicates that the selectivity on the modified ruthenium catalyst in the pressure range of 0.51–8.08 MPa is a maximum at .

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-2--І Ru Ru–ZnO-. , 0,51–8,08 , .

     

Displacement of hydrogen from rhodium surface by carbon monoxide under conditions of pulsed-gas chromatography

Interaction of carbon monoxide with hydrogen on the surface of rhodium catalysts has been investigated under conditions of pulsed-gas chromatography within the temperature range of –80 to 500 °C. At temperatures up to about 180 °C adsorbed hydrogen was found to be displaced to the gaseous phase as a result of carbon oxide adsorption. At higher temperatures conversion of carbon monoxide and hydrogen to methane takes place.

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–80 500 °C. 180 °C . .

     

Application of thermokinetics in chemical process analysis,as illustrated by the reaction of phenyl isocyanate andn-Butanol

Shortening the time required for chemical process development from the first laboratory trial through technical and pilot plants to industrial installation is a long-standing aim. Knowledge of the reaction kinetics is of major importance for this purpose. The usefulness of thermokinetics in chemical process engineering is illustrated by reaction of phenyl isocyanate andn-butanol.

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Zusammenfassung Die Abkürzung der Verfahrensentwicklung vom ersten Laborversuch über Technikums- und Pilotanlagen bis zur großtechnischen Anlage ist ein seit langem erstrebtes Ziel. Dabei ist bekanntlich die Kenntnis der Reaktionskinetik von großer Bedeutung. Am Beispiel der Reaktion Phenylisocyanat undn-Butanol wird die Nützlichkeit der Thermokinetik in der chemischen Verfahrensentwicklung aufgezeigt.

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, , , . . -.

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n-Hexane dehydrocyclization over Pt?Ni supported on alumina catalysts

Pt–Ni/-Al₂O₃ catalysts have been prepared and studied in n-hexane dehydrocyclization. The selectivity for benzene and toluene, a chain lengthening product formation was improved by Ni and correlated with its content.

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Pt–Ni/-Al₂O₃ -. Ni . Ni , .

     

Effect of the state of vanadium cations on the IR spectra of adsorbed carbon monoxide

ESR and IR-spectrosocpic studies of the effect of the state of vanadium ions on the IR-spectra of adsorbed CO have revealed complex formation of CO with V⁴⁺ (vCO at 2192 and 2205 cm^–1) and V³⁺ (vCO at 2178 and 2185 cm^–1) ions.

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-- - CO. CO V⁴⁺ (vCO 2192, 2205 cm^–1) V³⁺ (vCO 2178, 2185 cm^–1).

     

Quantitative parameters by thermoanalytical methods

The conditions and premises of the kinetic evaluation of thermoanalytical curves on the basis of chemical kinetics are demonstrated, and the limits of their availability are pointed out. For reactions with an unclear structural and chemical course, some appropriate definitions of terms are proposed.The possibilities of the use of the inflection points of the reaction rate versus time curve are presented. New methods of determination of kinetic parameters are described, including the ratio of the degrees of reactionx, the ratio of the reaction ratesx and the ratio of the tangent slopesx at these points.

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Zusammenfassung Bedingungen und Voraussetzungen der kinetischen Auswertung thermoanalytischer Meßkurven auf der Basis der chemischen Kinetik werden dargestellt, gleichzeitig wird auf die Grenzen ihrer Gültigkeit hingewiesen. Für Reaktionen mit unklarem chemischem oder strukturellem Ablauf werden geeignete neue Bezeichnungen definiert.Die Möglichkeit zur Verwendung der Wendepunkte der Kurve Reaktionsgeschwindigkeit gegen Zeit vorgestellt. Neue Methoden werden beschrieben, die zur Bestimmung kinetischer Parameter das Verhältnis der Umsätzex ₁ x ₂, das Verhältnis der Reaktionsgeschwindigkeitenx ₁/x ₂, und das Verhältnis der Tangentensteigungenx ₁/x ₂ an den Wendepunkten verwenden.

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. . . — . , (x), () () .

     

Hydration studies on the system pulverized fly ash—Ca(OH)2-CaCl2 using DTA and TG

Differential thermal analysis and thermogravimetry were used to monitor the course of hydration in the system fly ash - Ca(OH)₂ - CaCl₂. It was shown that the CaCl₂ admixture is an activating agent in this system. The results should be used for the correction of the mixture ratio of binders and builiding materials based on fly ash.

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Zusammenfassung Mittels DTA und Thermogravimetrie wurde die Hydratation im System Flugasche-Ca(OH)₂-CaCl₂ verfolgt. Dabei wurde gefunden, dass CaCl₂ in diesem System als Aktivator wirkt. Die Ergebnisse sollen zur Korrektur des Mischungsverhältnisses von Bindemitteln und Baumaterialien auf Basis Flugasche verwendet werden.

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-()₂-l₂, , . .

     

Asymmetric hydrogenation of tryptophan precursors catalyzed by rhodium-DIOP complexes

Z-2-benzamido(acetamido)-3-(3-indolyl)-2-propenoic acids were hydrogenated with neutral and cationic rhodium(I) complexes containing the chiral diphosphine (–) or (+)–2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-butane [(–) or (+)–DIOP].

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Z-2- ()-3-(3-)-2- () (I), (–) (+)-2,3--2,3--1,4- ()-.