Kinetic and mechanistic studies on the oxidation of arginine and histidine by chloramine-T in hydrochloric acid medium

The oxidation of amino acids by chloramine-T (CAT) in HCl medium at 30°C indicates simultaneous catalysis by H⁺ and Cl^– ions in the HCl concentration range of 0.04–0.12 M. The reaction is first order with respect to concentrations [CAT], [H⁺] and [arginine], but zero order with respect to [histidine]. The rate depends also on Cl^– concentration following 0.7th order. At HCl concentrations >0.12 M, the rate equation is:w=k[CAT] [amino acid]^0.6 and is independent of the [Cl^–]. A suitable mechanism has been suggested.

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-T (CAT) HCl (30°C) H⁺, Cl^– [HCl]=0,04–0,12M. [CAT], [H⁺] [] []. [Cl^–]^0,7. [HCl]>0,12M =k · [CAT][]^0,6 [Cl^–]. .

     

Thermodynamics and thermochemistry of kinetic (real) phase diagrams involving solids

A theoretical analysis of the formation of materials with metastable microstructures under non-ideal and highly non-equilibrium conditions is presented.

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Zusammenfassung Es wird eine theoretische Untersuchung der Bildung von Stoffen mit metastabilen MikroStrukturen unter nichtidealen Bedingungen weitab vom Gleichgewicht dargelegt.

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.

     

Investigation of thermal degradation of polymers containing chlorine by thermogravimetry

The thermal degradation of chlorine-containing polymers used in a rubber technology has been investigated in a nitrogen atmosphere. The characteristics of degradation have been compared on the basis of thermogravimetry, carbon residues and chlorine elimination. The observed structure-dependent differences in degradation of the investigated polymers are discussed.

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Zusammenfassung Die thermische Zersetzung von in der Kautschuk-Technologie verwendeten chlorhaltigen Polymeren wurde unter Stickstoff untersucht.Die Charakteristika der Zersetzung durch die Thermogravimetrie, Kohlenrückstand und Chlorabspaltung wurden verglichen. Die in der Zersetzung der untersuchten Polymere in Abhängigkeit von ihrer Struktur beobachteten Unterschiede wurden diskutiert.

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Résumé On a étudié, en atmosphère d'azote, la dégradation thermique des polymères contenant du chlore, utilisés dans la technologie du caoutchouc.On a comparé les caractéristiques de la dégradation par thermogravimétrie, formation d'un résidu de carbone et élimination du chlore. On discute les différences observées dans la dégradation des polymères étudiés suivant leur structure.

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, . . .

     

Effect of surfactants on the cleavage of the N?O bond in O-(2,4-dinitrophenyl)-cyclohexanone oxime

Kinetics of cleavage of N–O bond in O-(2,4-dinitrophenyl)-cyclohexanone oxime with hydroxide ions both in the presence and absence of surfactants has been studied. The reaction is accelerated by cationic micelles, slightly by non-ionic micelles and there is no effect of anionic micelles. A plot of the rate constant vs. [surfactant] shows a maximum corresponding to the CMC of surfactant.

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NO O-(2,4-) - , - (). , , - . , .

     

Evolved gas analysis for examination of surface oxides on alloys

Temperature programmed reduction in a hydrogen flow with simultaneous evolved gas analysis was employed to determine surface oxides on oxide dispersion strengthened (ODS) nickel containing TiO₂, A1₂O₃ or Cr₂O₃ particles, and on a Ni-2OCr alloy, after exposure to air at elevated temperatures. Oxides on particles of water-atomized (WA) Ni-2OCr powder were analysed similarly. Significant differences in starting temperatures of the reaction between hydrogen and phases present in oxide layers made identification of the phases possible. NiO or NiO doped with Ti, Al or Cr are the major constituents of the scale formed on ODS Ni. NiTiO₃, NiCr₂O₄ and NiAl₂O₄ are formed as a result of a reaction between TiO₂, A1₂O₃ or Cr₂O₃ particles in the scale with NiO. The oxide layer formed on Ni-2OCr alloy consists of Cr₂O₃ and of NiO doped with Cr. Surface oxides on WA Ni-2OCr contain Cr₂O₃ and a small amount of NiO.

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Zusammenfassung Temperaturprogrammierte Reduktion im Wasserstoffstrom wurde zusammen mit gleichzeitiger Analyse des in Freiheit gesetzten Gases dazu benutzt, um Oberflächenoxide an Nickel enthaltenden TiO₂-, A1₂O₃- oder Cr₂O₃-Partikeln mit verstärkter Oxiddispersion (ODS) und an einer Ni-2OCr-Legierung nach Behandlung in Luft bei erhöhten Temperaturen zu bestimmen. Oxide auf Partikeln von wasser-zerstäubtem (WA) Ni-2OCr-Pulver wurden auf ähnliche Weise analysiert. Signifikante Unterschiede in der Starttemperatur der Reaktionen zwischen Wasserstoff und der in den Oxidschichten vorliegenden Phasen ermöglichen die Identifikation der Phasen. NiO oder mit Ti, Al oder Cr gedoptes NiO sind die Hauptbestandteile des auf ODS-Ni gebildeten Belags. NiTiO₃, NiCr₂O₄ und NiAl₂O₄ treten als Produkte der Reaktion von TiO₂-, Al₂O₃- oder Cr₂O₃-Partikeln mit NiO im Belag auf. Die auf der Ni-2OCr-Legierung gebildete Oxidschicht besteht aus Cr₂O₃ und aus mit Cr gedoptem NiO. Oberflächenoxide auf WA-Ni2OCr enthalten Cr₂O₂ und geringe Mengen an NiO.

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- , , , , , , Ni-2r, . Ni-2OCr. , , . , , , , . NiTiO₃, NiCr₂O₄ NiAl₂O₄ , , . , Ni-2r, , . Ni-2r .

     

Precipitation of iron catalysts for the Fischer-Tropsch synthesis

The batch Fischer-Tropsch wise precipitation of iron catalysts for the synthesis in the pH range of 4.60 to 7.91 is described in detail. Each step of the precipitation has been controlled by measurements of the relevant parameters to produce definite catalysts. Factors influencing the reproducibility are shortly discussed.

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- pH=4,60–7,91. . , .

     

Thermal studies on titanyl,zirconyl and hafnyl dithiocarbamato complexes

The dithiocarbamato complexes of titanyl(IV), zirconyl(IV) and hafnyl(IV), abbreviated as MO(S₂CNRR)₂·nH₂O(M=Ti, Zr or Hf,R=H,R=C₅H₉;R=H,R=C₇H₁₁,n=1 for Ti andn=2 for Zr and Hf), were prepared in aqueous medium and characterized by elemental analyses, magnetic susceptibility measurements and IR spectral studies. The thermal behaviour of these compounds under non-isothermal conditions was investigated by thermogravimetric, derivative thermogravimetric and differential scanning calorimctric techniques in nitrogen and oxygen atmospheres. The intermediates obtained at the end of various thermal decomposition steps were identified on the basis of analyses and IR spectral studies. Kinetic parameters, such as apparent activation energy and order of reaction, were determined by the graphical method of Coats and Redfern. The heats of reaction for the different decomposition steps were calculated from the DSC curves.

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Zusammenfassung Die Thiocarbamato-Komplexe von Titanyl(IV), Zirkonyl(IV) und Hafnyl(IV) der allgemeinen Formel MO(S₂CNRR)₂·n H₂O (M=Ti, Zr oder Hf;R=H, R=C₅H₉;R=H, R=C₇H₁₁;n=1 für Ti undn=2 für Zr und Hf) wurden in wässrigem Medium hergestellt und durch Elementaranalyse, Messung der magnetischen Suszeptibilität und IR-Spektraluntersuchungen charakterisiert. Das thermische Verhalten dieser Verbindungen unter nicht-isothermen Bedingungen wurde durch TG, DTG und DSC in Stickstoff- und Sauerstoffatmosphäre untersucht. Die nach verschiedenen thermischen Zersetzungsschritten erhaltenen Zwischenprodukte wurden durch chemische Analyse und IR-Spektroskopie identifiziert. Kinetische Parameter, wie die scheinbare Aktivierungsenergie und die Reaktionsordnung, wurden nach der graphischen Methode von Coats und Redfern bestimmt. Für die einzelnen Zersetzungsschritte wurden die Reaktionswärmen aus den DSC-Kurven berechnet.

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, . MO(S₂CNRR)₂·nH₂O (M=I, Zr, Hf,R=H,R ¹=C₅H₉, C₇H₁₁,n=1 I =2 ) , . , . , , . - . .

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The authors are grateful to Dr. Shyam Kumar for helpful discussions.     

Thermogravimetry. Fast methods for evaluation of kinetic parameters

The paper discusses three fast methods for determination of the reaction order, as follows: the single-point method proposed by Kissinger, Horowitz and Metzger, an original two-point method, and the three-point method suggested by a Gorbachev's paper. These methods cannot elucidate the reaction mechanism, but they can help in the rapid derivation of the apparent kinetic parametersn andE.

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Zusammenfassung Es wurden drei Methoden zur Schnellbestimmung von Reaktionsordnungen ausgewertet: eine Einpunktmethode von Kissinger, Horowitz und Metzger, eine Zweipunktmethode und eine Dreipunktmethode nach einer Anregung von Gorbachev. Mittels dieser Methoden kann man zwar nicht den Reaktionsmechanismus bestimmen, wohl aber eine schnelle Bestimmung der kinetischen Scheinparametern undE durchführen.

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: , , , , . , n .

     

Differential scanning calorimetry of chloroquine sulphate exposed to sun,heat and ultraviolet radiation

Chloroquine sulphate, like the phosphate, is an antimalarial formulation widely used in the tropics. The stability of such formulations is therefore of interest in the combat against malaria. A DSC study has been made of the effects of exposure to the sun, heat and UV radiation on the stability of chloroquine sulphate, similarly as performed earlier for chloroquine phosphate. When freshly recrystallized from a water-acetone mixture, chloroquine sulphate exhibits two endothermic peaks, at 169.4° and 204.7°, for the expulsion of crystal water (one molecule) and for the melting process, respectively. The exposure of chloroquine sulphate to the sun, heat and UV radiation leads to splitting of the peak for melting.

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Zusammenfassung Chloroquine-Sulfat ist ebenso wie das entsprechende Phosphatderivat ein in den Tropen weitverbreitet angewandtes Antimalaria-Präparat. Die Stabilität dieses Präparates hat damit Bedeutung für die Malariabekämpfung. Die vorliegende Arbeit ist eine Erweiterung einer Untersuchung über den Effekt der Einwirkung.von Sonne, Hitze und UV-Strahlen auf die Stabilität von Chloroquine-Phosphat auf Chloroquine-Sulfat. Aus Wasser-Aceton-Mischungen frisch kristallisiertes Chloroquine-Sulfat zeigt zwei endotherme Peaks bei 169,4 und 204,7 °C, die durch Abgabe von Kristallwasser (ein Molekül) bzw. durch den Schmelzvorgang bedingt sind. Wird Chloroquine-Sulfat der Sonne, Wärme oder UV-Licht ausgesetzt, so wird der dem Schmelzvorgang zuzuscheibende Peak aufgespalten.

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, -, , . . , . , , 169,4 204,7°, , , . , .

     

Effect of the medium on the oxidation of aliphatic monocarboxylic acids

Oxidation rates and k₂/k₆ ratios are given for some acids from propionic to lauric. The k₂/k₆ ratio is shown to be influenced by the electrostatic effect of the solvent. A linear dependence between the isodielectric values of k₂/k₆ and the number of methylene groups in the acid molecules is described.

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k₂/k₆ . k₂/k₆ k₂/k₆ .

     

Mechanism of carbon monoxide oxidation on nickel oxide and its solid solutions

On the basis of studying the isotope exchange of oxygen and the position of the Fermi level in the system MiO–Li_xNi_1–xO, an explanation is proposed for the compensation effect in the reaction of CO oxidation on nickel oxide and its solid solutions.

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NiO–Li_xNi_1–xO CO .

     

The kinetics of Ln2O3 Hydration under mild conditions

The kinetics of Ln₂O₃ hydration (Ln=Sm, Ho, Yb, Lu) have been studied at room temperature and atmospheric pressure, as have the influence of the activation temperature and the method of preparation of the oxides.The best correlation coefficients are obtained for a diffusion mechanism. If a structural relationship between the C-Ln₂O₃ and their precursors is considered, the possibility arises of the existence of defect planes in the oxides prepared from the hydroxide and carbonate. This facilitates the hydration process through a diffusion mechanism in the case of the rare earth sesquioxides prepared from the above precursors.

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Zusammenfassung Die Kinetik der Hydratisierung von Ln₂O₃ (Ln=Sm, Ho, Yb, Lu) wurde bei Raumtemperatur und atmosphärischem Druck bezüglich des Einflusses der Aktivierungstemperatur und der Art der Darstellung der Oxide untersucht. Die besten Korrelationskoeffizienten werden für einen Diffusionsmechanismus erhalten. Wenn die strukturelle Beziehung zwischen den C-Ln₂O₃ in Betracht gezogen wird, so ergibt sich die Möglichkeit der Existenz von defekten Gitterebenen in den aus Hydroxiden und Carbonaten hergestellten Oxiden. Dies erleichtert den Hydratisierungsprozeß durch einen Diffusionsmechanismus im Falle von aus den oben genannten Vorstufen hergestellten Sesquioxiden der Seltenen Erdmetalle.

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Ln₂O₃, Ln=Sm, Ho, Yb, Lu, . . , , . .

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We thank the CAICYT (Project No. 1377/82) for financial support.     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

Coked reforming catalysts: Self-regeneration by residual hydrogen

The deactivation and subsequent self-regeneration of several Pt/–Al₂O₃/honeycomb reforming catalysts have been investigated. Catalytic activity in the dehydrogenation of methylcyclohexane (MCH), taken as reaction model, has been evaluated at 400 °C in a continuous flow microreactor. The determining role of surface chlorine during the H₂ self-regeneration of catalysts is discussed. A catalyst with ca. 0.5% C1 shows complete self-regeneration. A regeneration mechanism, involving the spillover of residual hydrogen, is proposed.

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Pt/–Al₂O₃ . , , 400°C . . . 0.5% Cl . , .

     

Experimental study of the bifurcation diagram in the Belousov-Zhabotinskii reaction

In the citric acid-Mn²⁺–H₂SO₄–KBrO₃ system a hysteresis phenomenon in the switching on and off of the oscillations has been observed. The possible bifurcation diagrams of the system are discussed.

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-Mn⁺²–H₂SO₄–KBrO₃ . .

     

Nature of the active oxygen of Co3O4

The differentiation of surface oxygen forms of Co₃O₄ by energy, reactivity and centers of adsorption has been carried out.

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Co₃O₄ , .

     

Toluene disproportionation and coke formation over fluorided alumina and hydrogen-mordenite

Toluene transformation was investigated on a fluorided alumina and a protonic mordenite under hydrogen (0.8, 12 bar) and under nitrogen (12 bar). Hydrogen pressure considerably improves the catalytic stability of H-mordenite by inhibiting the formation of coke. Moreover, hydrogen eliminates part of the coke deposited by reaction under nitrogen, and regenerates the activity of the mordenite. On the contrary, hydrogen has no effect in the case of fluorided alumina. The particular behavior of the mordenite is attributed to its very strong acidity.

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(0,8, 12 ) (12 ). -, . , , , . , - . .

     

Study of well-characterized Pt?Ru/C catalysts by oxygen electroreduction

A series of well characterized Pt–Ru bimetallic catalysts supported on graphite has been studied by means of the electroreduction of oxygen in a supporting electrolyte of 1 N H₂SO₄. A synergetic effect is observed when the activity per gram of catalyst is considered. However, this effect disappears when the activity values are corrected by the active surface area.

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Pt–Ru, , 1N H₂SO₄. 1- , . , , .

     

Energy dissipation and selectivity in the catalytic oxidation of ammonia

A qualitative interpretation of selectivity changes in ammonia oxidation, based on considerations of energy dissipation processes is presented.

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, .