Kinetics and mechanism of the oxidation of L-ascorbic acid by 2,6-dichlorophenol-indophenol in aqueous solution

The kinetics of oxidation of L-ascorbic acid by 2,6-dichlorophenolindophenol in aqueous solution has been studied. The rate of the reaction decreases with increasing pH since the hydrogen ascorbate ion is less reactive than the unionized L-ascorbic acid. The rate constants for the oxidation of the two species have been evaluated and a plausible mechanism of the reaction is suggested.

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L- 2,6-- . pH, , L- . .

     

Kinetics and mechanism of oxidation of D-altrose by aqua-cerium(IV) in perchloric acid medium

Kinetics of the oxidation of D-altrose by Ce(IV) perchlorate has been studied in perchloric acid medium. At equivalent concentrations the overall order of the reaction is two, being unity in each reactant. The reaction is characterized by a primary positive kinetic salt effect. Perchloric acid has been found to enhance the rate, while the addition of the reaction products retards the rate. No evidence for initial complexation has been obtained. Thermodynamic parameters have been determined and a mechanism consistent with the observed results is proposed.

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D- Ce(IV) . , . . , . . , .

     

On the reduction of NiO forms in magnesia supported catalysts

Reducibility of Ni/MgO catalysts has been studied by the temperature-programmed reduction (TPR) technique in the temperature range of 373–1273 K. The profile of reduction reveals the presence of various forms of NiO. The effects of nickel loading and treatment temperature on catalyst reducibility have been evaluated. The formation of NiO–MgO solid solution controls the whole reduction of Ni/MgO system.

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Ni/MgO 373–1273 . NiO. . Ni/MgO NiO–MgO.

     

Calculation of the mass transfer coefficient with a chemical reaction in a gas-liquid system

A solution of the problem of mass transfer in a turbulent boundary layer has been obtained with a first-order chemical reaction occurring in the liquid phase. The dependence of the enhancement factor for absorption and of the mass transfer coefficient on the model parameters can be used for building up a hierarchic model of the gas-liquid reactor.

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Interaction of V2O5 with oxygen in the gas phase

Sorption/evolution of oxygen from V₂O₅ in the temperature range of 480–520°C is due to a shift in the defect equilibrium 1/2 O₂ (gas)+V_oO_o. A first-order kinetic equation can be derived under the assumption that the activation energy depends on the concentration of defects.

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/ V₂O₅ 480–520°C 1/2 O₂ ()+V_oO_o. , , .

     

The thermometric and enthalpimetric determination of organic compounds

Two main parameters determine the methods for the assay of organic compounds in industrial systems; these are the rates of reaction of the molecular organic and often non-aqueous systems which differ from those in ionic and aqueous systems, and secondly, the fact that in most organic systems an organic functional group is required to be determined by a general method applicable to the functional group in a variety of chemical environments. In pharmaceutical products it is desired to determine the functional groups without prior separation from excipients of various kinds and to obtain rapid assays, often with precision much lower than those normally required in inorganic systems. These methods are discussed with examples taken from the foodstuff industry, the pharmaceutical industry, etc.

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: , . , - , . . , . , , .

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Partly presented at the II. Seminar Thermometric Analysis, Budapest, September 2–7, 1980.     

A study of the surface heterogeneity and catalytic activity of catalysts by means of reaction thermodesorption

Reaction thermodesorption is studied. A generalized wiew is offered regarding the routes along which the transformations take place under the conditions of temperature-programmed desorption.

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. , .

     

Kinetics of CO hydrogenation on group VIII metals

Kinetics of CO hydrogenation on supported Group VIII metals has been studied. Kinetic equations for CO methanation and Fischer-Tropsch synthesis suggested previously are consistent with the experimental data obtained.

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CO VIII . CO -, , .

     

DSC and vapour pressure investigation of some β-diketonates

DSC and vapour pressure measurements are presented on some Be, Al and Cr complexes with 2,4-pentanedione tetramethyl-3,5-heptanedione, 1,1,1-trifluoro-2,4-pentanedione and hexafluoro-2,4-pentanedione. Thermodynamic functions are given for the sublimation, vaporization and melting processes of the substances.

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Zusammenfassung Die Ergebnisse von DSC- und Dampfdruckmessungen einiger Komplexe von Beryllium, Aluminium und Chrom mit 2,4-Pentandion (HAA), Tetramethyl-3,5-heptandion (HTHD), 1,1,1-Trifluoro-2,4-pentandion (HATA) und Hexafluoro-2,4-pentandion (HHFA) werden beschrieben. Die berechneten thermodynamischen Funktionen für Sublimation, Verdampfung und Schmelzen der Komplexverbindungen sind tabelliert.

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, 2,4- , 1,1,1-- -2,4- -3,5- . , .

     

Rh and Pt catalysts activated by UHV treatments

The H₂–D₂ exchange activity of Rh powder was enhanced by high-temperature UHV treatment accompanied with an enrichment of the high-index faces of Rh. The thermal decomposition of H₂PtCl₆·6H₂O under UHV condition resulted in an extremely active Pt powder catalyst.

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H₂–D₂ Rh , - Rh - . H₂PtCl₆·6H₂O Pt .

     

Kinetics of catalyst regeneration by coke combustion. II. Influence of temperature rise in the catalyst particles

A grain-pellet model has been used to study the effect of high reaction rates upon the temperature profiles developed during regeneration of coked catalyst particles. The possibility of falsification of kinetic data is discussed in view of the results obtained.

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- , . .

     

The Chemistry of Methane Remediation by a Non‐thermal Atmospheric Pressure Plasma

The destruction of methane by a nonthermal plasma in atmospheric pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the endproducts are determined by online FTIR spectroscopy and the plasma chemistry is interpreted using kinetic modelling. For a deposited energy of 118 kJ m^–3, the destruction is 12% in nitrogen decreasing monotonically to 5% in air. The major endproducts are HCN and NH₃ in nitrogen and CO, CO₂, N₂O, NO and NO₂ for gas streams containing oxygen. The chemistry in pure nitrogen is predominantly due to reactions of electronicallyexcited nitrogen atoms, N(²D). The addition of oxygen converts the excited state nitrogen into nitrogen oxides reducing the methane destruction which then arises by O and OH reactions yielding CO and, to a lesser extent, CO₂. The modelling correctly predicts the magnitude of the methane destruction as a function of added oxygen and the concentrations of the endproducts for processing in both nitrogen and air.     

Steric substituent effect on the resin catalyzed hydrolysis of alkyl acetate esters

The rates of hydrolysis of seven acetate esters substituted in the alkyl group have been studied in the presence of a sulfonated cation exchange resin in 70% aqueous acetone solution. the slower hydrolysis rates with increasing size of substituent are related to increasing steric influence, as determined by decreasing values of the steric substituent parameter, E_s. The efficiency of the resin catalyst is related to the entropy of substituents. Influence caused by steric hindrance on reaction rates accounts satisfactorily for observed variations of the enthalpies and entropies of activation with alkyl group substituents. The entropy, S^x, values increase in the order: n-octyl-

, , 70%- . , , E_S. . , . , S^*, : --<-<, .

     

On the initial treatment of kinetic data

The kinetic methods usually employed to determine reaction orders involve some sort of mathematical approximation and provide values approximate and very often discrepant. Three methods are reported to determine accurate reaction orders without introducing approximations.

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, , , , . .

     

Isothermal crystallization measurements on copolyesters by differential scanning calorimetry

Miller's method for isothermal crystallization measurement was used to determine the progress of crystallization of copoly(ethylene terephthalate/isophthalate) and copoly(ethylene terephthalate/5-methoxyisophthalate) by DSC. The evaluation of kinetic parameters is too complicated for higher contents of comonomer and higher values of molecular mass of copolyesters. On the other hand, the experimental results interpreted by the simplified equation well characterized the differences in the rates of crystallization of different copolyesters.

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Zusammenfassung Die Millersche Methode der isothermen Kristallisierung wurde eingesetzt um den Fortschritt der Kristallisierung von Kopoly(Äthylen-Terephthalat/Isophthalat) und Kopoly(Äthylen-terephthalat/5-Metoxyisophthalat) mittels DSC zu untersuchen. Die Auswertung der kinetischen Parameter ist für höhere Ko-Monomergehalte und höhere Molekularmassenwerte der Ko-Polyester zu kompliziert. Andererseits konnten die an Hand der vereinfachten Gleichung gedeuteten Versuchsergebnisse zur Charakterisierung der Unterschiede der Kristallisierungsgeschwindigkeiten der verschiedenen Ko-Polyester mit gutem Erfolg eingesetzt werden.

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Résumé On a appliqué la méthode de détermination de la cristallisation isotherme de Miller à la détermination par analyse calorimétrique différentielle de l'avancement de la cristallisation du copoly(éthylène téréphtalate/isophtalate) ainsi que du copoly(éthylène téré phtalate/5-méthoxy-isophtalate). L'évaluation des paramètres cinétiques est trop compliquée pour les teneurs plus élevées en comonomère et pour les valeurs plus élevées de la masse molaire des copolyesters. D'autre part, les résultats d'expériences interprétés par l'équation simplifiée ont bien caractérisé les différences de vitesses de cristallisation des divers copolyesters.

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. : Ni(NCS)₂(py)₄, (=), CuSO₄ · 5₂ NiSO₄ · 7₂, . , , .

     

Simultaneous TG,DTG, DTA and EGA technique for the determination of carbonate,sulphate, pyrite and organic material in minerals,soils and rocks

A simultaneous TG, DTG, DTA and EGA method was developed for the determination of carbonate, sulphate, pyrite and organic material in minerals. The method is based on the selective direct determination of SO₃ and CO₂ evolved from the heated sample, and on the indirect determination of H₂O. The thermogas-titrimetric adapter of the derivatograph collects the liberated gases (CO₂, SO₃, SO₂) quantitatively, absorbs them in water, and titrates them continuously and automatically with NaOH titrant. The changes in the volume of titrant consumed are recorded as a function of the temperature. In two parallel examinations, one titration is performed at pH 4, and the other at pH 9.3. The former measurement yields only the amount of SO₃ (SO₂), while the latter gives the joint amount of SO₃ (SO₂) and CO₂.

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Zusammenfassung Autoren entwickelten eine Methode zur simultanen TG, DTG, DTA und EGA zur Bestimmung von Karbonaten, Sulfaten Pyrit und organischem Material in Mineralen. Die Methode basiert auf der selektiven direkten Bestimmung des beim Erhitzen der Probe entwickelten SO₃ bzw. CO₂ und der indirekten Bestimmung von Wasser. Die in Freiheit gesetzten Gase (CO₂, SO₃, SO₂) werden im gastitrimetrischen Adapter des Derivatographen gesammelt, in Wasser absorbiert und kontinuierlich und automatisch mit NaOH titriert. Das Volumen der verbrauchten Titrierflüssigkeit wird in Abhängigkeit von der Temperatur registriert. In zwei Parallelversuchen wird eine Titration bei pH 4, die andere bei pH 9.3 ausgeführt. Die erstere Messung ergibt nur die Menge an SO₃ (SO₂), während bei der letzteren die Gesamtmenge an SO₃ (SO₂) und CO₂ erhalten wird.

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, , ( ) , , . SO₃ CO₂, , . - (CO₂, SO₃, SO₂), . ë . : pH=4, - pH=9.3. SO₃(SO₂), — SO₃(SO₂) CO₂.

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

Influence of the chlorine content of Al2O3 on its catalytic activity and coke formation

The catalytic activities of aluminas with different chlorine contents for cumene cracking, o-xylene isomerization, n-hexane isomerization and cracking and methylcyclopentane cracking were studied. The catalytic activity and the acidity increase continuously when the chlorine content increases. Coke formation is only noticiable with methylcyclopentane, increasing with the chlorine content of the alumina.

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, -, - . . - , - .

     

Photochemical reactions of anthraquinone with hydrocarbons in the presence and absence of oxygen: Trapping of radical intermediates

Radical intermediates formed at 25°C in the presence and absence of oxygen during the photolysis of anthraquinone in aromatic, cyclic and aliphatic hydrocarbon solvents were trapped by 2,6-dichloronitrosobenzene, 2,6-dibromonitrosobenzene and 2,4,6-tribromonitrosobenzene. The resulting nitroxide radicals have been characterized in situ by ESR spectra.

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: 2,6-, 2,6- 2,4,6-— , , 25°C. .

     

Error analysis of surface area determinations by the chromatographic technique

The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.

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