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^–]. .

     

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 . .

     

Catalytic preparation of mesityl oxide from acetone

In the process of the aldol condensation of acetone the preparation of mesityl oxide has been studied with respect to the temperature and the nature of catalyst. Strong basic ion exchangers Ionenaustauscher III (Merck III) and Lewatit MP 500 were used in the temperature range from 0 to 50°C. Better results are achieved with Merck III, as is evident from DAA/MO yields, rate constants and energy activation values. Empirical expressions for DAA/MO production are given.

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(). Ionenaustauscher III (Merck III) Lewatit MP 500 0 50°C. / (= ), , Merck III. - /.

     

The direction of elimination in the pyrolysis kinetics of 3-bromobutyronitrile

The gas phase elimination of 3-bromobutyronitrile, examined in a static system and seasoned vessel, follows a first-order rate law. The reaction in the temperature range of 370.0–420.1°C and pressure range of 54–198 torr, is homogeneous and unimolecular. The temperature dependence of the rate coefficient is given by the equation: log k₁ (s^–1)=(13.74±0.25)–(213.7±3.2) kJ mol^–1 (2.303RT)^–1. The cyano substituent has been found to retard the elimination process through its electronwithdrawing resonance effect. Most of the dehydrobromination product is cis-trans-crotonitrile, while very little of allyl cyanide is obtained. This result is rationalized in terms of electronic factors.

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3- , . . 370,0–420,1°C 54–198 . : log k₁ (cek^–1)=(13,74±0,25)–(213,7±3,2)(/)×(2,303 RT)^–1. - . --, . .

     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Mechanism of ring expansion in 1-ethylindane under dehydrogenation conditions

Studies of 1-ethyl-(-¹⁴C)-indane dehydroisomerization over a Pt/Al₂O₃ catalyst (AP-64) have revealed that 34.5% or 16.5% of the initial tracer label migrates into the -position of the expanded methylnaphthalene ring when the catalyst is pretreated at 763 K in Ar or H₂, respectively. The reaction mechanism is discussed.

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1--(¹⁴C)- -64. , 763 - 34,5% , —16,5%. .

     

Linear free energy relations in solid state reactions II

Kinetics of the reaction between solid cobalt(II) acetate and solid substituted aniline hydrochlorides have been studied by thermal analysis. All the reactions go to completion. The crystalline products were characterized by physico-chemical methods. The energy of activation is 83.4,44.2,64.2,100.9,79.8,99.9, 135.9 and 168.7 kJ mol^–1for the reactions of aniline, 3- and 4-chloro-, 4-iodo-, 4-bromo-, 4-fluoro-, 4-methyl- and 4-methoxy aniline hydrochlorides with cobalt acetate. A plot of energy of activation against Hammett's constant is linear with a slope of –169.9 kJ mol^–1. A comparison between the reactivity of these reactions by the capillary and the thermal methods has been done.

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Zusammenfassung Mittels Thermoanalyse wurde die Kinetik der Festkörperreaktion zwischen Kobalt(II)azetat und substituierten Anilinhydrochloriden untersucht. Alle Reaktionen laufen vollständig ab. Die kristallinen Produkte wurden mittels physikalisch-chemischer Methoden charakterisiert. Die Aktivierungsenergie der Reaktion von Kobalt(II)azetat mit Anilin, 3- und 4-Chlor-, 4-Jod-,4-Brom-, 4-Fluor-, 4-Methoxy- und 4-Methylanilin beträgt 83.4,44.2,64.2,100.9,79.8,99.9,168.7 bzw. 135.9 kJ/mol. Bei der Darstellung der Aktivierungsenergie in Abhängigkeit von der Hammettkonstante konnte Linearität mit einem Anstieg von – 169.9 kJ/mol festgestellt werden. Die Reaktivität dieser Reaktionen wurde mittels Kapillar- und thermischen Verfahrens verglichen.

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. . - . , 3- 4--, 4--, 4--, 4--, 4- - 4- , , 83,4; 44,2; 64,2; 100,9; 79,8; 99,9; 135,9 168,7 ·^–1. - –169,9 ·^–1. , .

     

Discrimination of active sites for ethylene homologation and ethylene metathesis on molybdena silica catalyst

Active sites for ethylene homologation (3C₂H₄2C₃H₆) and ethylene metathesis (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) were discriminated by adding platinum to a reduced molybdena silica catalyst, and the former was presumed to be composed of several molybdenum species, while the latter was presumed to be composed of one molybdenum species.

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(3C₂H₄2C₃H₆) (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) . , , .

     

Triterpene Glycosides of Fatsia japonica. VI. Structures of Glycosides D3a and D3b

Seeds of Fatsia japonica (Araliaceae) yielded the new glycosides of gypsogenin: 3-O--D-glucopyranosyl-(12)-O--D-glucopyranoside and 3-O--D-galactopyranosyl-(12)-O--D-glucopyranoside. The structures of these compounds were established by chemical methods and NMR spectroscopy.     

Substituierte 3-Amino-thiophene und 3-Amino-selenophene aus β-Chlor-α-cyan-zimtsäurenitril

Summary -Chloro--cyano-cinnamonitrile (1) reacts in one step with -oxo-thioles3 or successively with sodium sulphide and -chlorocarbonyl compounds4 to form the 5-substituted 4-amino-2-phenyl-thiophene-3-carbonitriles5. Analogously, the successive reactions of -chloro cinnamonitrile1 with sodium selenide — produced in situ from selene and sodium boronhydride — and -chlorocarbonyl compounds4 yields the 5-substituted 4-amino-2-phenyl-selenophene-3-carbonitriles6.

     

Sintering of supported palladium

Sintering results of Pd supported on carbon black at 723–973 K, in water vapor, in H₂ and under high vacuum are reported. They are compared with sintering data of Pd on other supports. The observed sequences are: SiO₂C>sepioliteAl₂O₃>AlPO₄ and H₂O>high vacuum>H₂.

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Pd 723–973 , , H₂ . Pd . : SiO₂Al₂O₃>AlPO₄ H₂O> >H₂.

     

On the deactivation of Fe2O3?MoO3/SiO2 catalysts in the oxidation of methanol to formaldehyde

The deactivation behavior of Fe₂O₃–MoO₃/SiO₂ catalysts with different Fe₂O₃+MoO₃ content in the oxidation of methanol to formaldehyde is investigated. A simplified reaction-deactivation kinetic model is presented and used to compare and discuss the different behaviors.

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Fe₂O₃–MoO₃/SiO₂ Fe₂O₃+MoO₃ . : -.

     

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), () () .

     

The relation between the nonlinear dielectric effect and solvent polarity

The relation between solvent polarity expressed through the Dimroth-Reichardt spectroscopic parameter E _T (30) and the nonlinear dielectric effect (NDE) expressed through the parameter /E² is demonstrated where is a change in the electric permittivity of a solvent in an external strong electric field E. Both E _T (20) and /E², determined in quite different ways, are extremely sensitive to the dielectric properties of a solvent which depend on molecular interactions. Linear correlations between /E² and E _T (30) have been found for n-alkanols representing hydrogenbond donor solvents, and for halogenobenzenes which are dipolar, aprotic, weakly-associated solvents.Part of this work was presented at The 22^nd International Conference on Solution Chemistry in Linz, Austria, July 1991.     

A variational formulation of the rate equations for closed chemical systems

This paper presents a variational formulation of the kinetic equations corresponding to a closed chemical system.

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, .

     

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. . , .

     

Kinetics and mechanism of the permanganate oxidation of trans-crotonic acid

The kinetics and intermediates of the permanganate oxidation of trans-crotonic acid have been investigated in the pH range of 0.5–5.0 using the stoppedflow technique. The formation of manganese(III) as a short-lived intermediate has been established. The reaction is first order with respect to both MnO ₄ ^– and crotonic acid (crotonate). The resolved rate constants at 25°C are 730 and 410 M^–1 sec^–1 for the acid and the anion, respectively. The reaction mechanism is discussed.

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pH=0,5–5,0, . (III) . MnO ₄ ^– , (). 25°C 730 410 M^{–1 –1} , . .

     

The reversibility of the octahedral → tetrahedral transition in bis(pyridine)-cobalt(III) chloride Co(py)2Cl2

The octahedral-tetrahedral structural transition of Co(py)₂Cl₂ was studied by high temperature reflectance spectroscopy and dynamic reflectance spectroscopy. The reversibility of the transition by standing at room temperature for 24 hrs was established.

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Zusammenfassung Es wurde durch Hochtemperatur-Reflexions-Spektroskopie und dynamische Reflexions-Spektroskopie bewiesen, daß die strukturelle Umwandlung des oktaedrischen Co(py)₂Cl₂ in die tetraedrische Form nach 24 stündigem Stehen bei Zimmertemperatur reversibel ist.

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Résumé On a pruvé par spectroscopie de reflexion de haute température et spectroscopie de reflexion dynamique la réversibilité de la transition structurale octaédrique-tetraédrique de Co(py)₂Cl₂ après 24 heures.

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— ë Co[Py]₂Cl₂ . 24 .

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The financial support of this work by the Robert A. Welch Foundation of Houston, Texas, is gratefully acknowledged. The assistance of Mr. Sherman Bradley is also acknowledged.