A novel possibility to clarify the role of bromide in bromate oscillators

Bromocomplex forming metal ions (Tl³⁺, Hg²⁺) alter considerably the parameters of chemical oscillations in bromate oscillators. Even at 10^–5 M metal ion concentration the period of the oscillation is doubled or tripled; at 10^–4 M the oscillation is quenched. At high (10^–2 M) Tl³⁺ concentration, high frequency, strongly damped oscillations occur although [Br^–]_eq is below 10^–10 M. By the addition of Tl³⁺ we could determine the amount of Br^– formed in a single autocatalytic step, which we found to be about 10^–4 M.

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(Tl³⁺, Hg²⁺), , . 10^–5 M , ; 10^–4 M . Tl³⁺ (10^–2 M) , [Br^–]_eq 10^–10 M. Tl³⁺ Br^–, , 10^–4 M.

     

Acetylacetonate of indium: Structure and reactivity with 1,3-dienes

The reaction of isoprene and 2,3-dimethyl-1,3-butadiene with indium tris-acetylacetonate, afforded C- and O-al-kylation products together with an oligomeric mass. A mechanism of diene transformation is proposed in which -diene-metal species could be involved.

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2,3--1,3- – - . , --.

     

Effect of carbon dioxide on the catalytic oxidation of ethylene over silver. Kinetic reaction model accounting for the modification of catalyst surface by carbonate groups

Changes in the character of catalytic oxidation of ethylene over silver upon increasing pressure of reaction mixture, reflected in increased ethylene oxide selectivity, are due to the modifying effect of suface carbonate groups. A kinetic reaction model is suggested based on the individual investigations of reaction steps.

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, , . , .

     

Zu einigen Besonderheiten des thermischen Zerfalls von Ni(II)-Komplexen mit dreizähnigen Schiffschen Basen

Zusammenfassung Es wurde eine Reihe von Komplexen des zweiwertigen Nickels mit den Schiffbasen H₂L,H₂L der Zusammensetzung NiL·ROH(R=Me, Et, Pr, i-Pr)und NiL ·ROH (R=Me, Et, Pr, i-Pr, Bu) hergestellt und deren thermischer Zerfall untersucht. Es wurde festgestellt, dass bei den Addukten NiL·ROH der Zerfall unter Abspaltung des Alkohols (Zwischenprodukt NiL) verläuft, während bei NiL·ROH sofort nach der Abspaltung des Alkohols zur Massenzunahme auf TG-Kurve durch Oxidation des Stoffes kommt. Das Plateau, das dem Zwischenprodukt NiL entspricht, ist hier nur in der Ineratmosphäre erhaltbar. Es wurden auch die Aktivierungsenergien für die Abspaltung des Alkohols berechnet.

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Ni(II) Schiff base complexes of compositions NiL ROH (R=Me, Et, Pr, i-Pr) and NiL·ROH (R=Me, Et, Pr, i-Pr, Bu) were prepared and investigated by methods of thermal analysis. The thermal decomposition of NiL·ROH led to NiL (plateau in TG curve), whereas NiL·ROH underwent a similar decomposition only in an inert atmosphere (N₂); thermal decomposition in air involved alcohol fragmentation, followed by a mass increase due to oxidation by atmospheric oxygen. The activation energy of alcohol fragmentation was calculated.

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NiL · ROH (R=-, -, - ) NiL-ROH (R=-, -, -, -, ). , NiL ] NiL — . , . .

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Wir möchten uns sehr herzlich bei Doz. RNDr. E. Jóna, CSc. und RNDr. I. Horváth, CSc. für die Messungen in der Stickstoffatmosphäre in SAV Bratislava bedanken.     

Determination of the rate constants for chain transfer with the monomer and hydrogen in Ziegler-Natta polymerization

The rate constants of chain transfer with the monomer and hydrogen in the polymerization of ethylene and propylene by the catalyst -TiCl₃. 0.3 AlCl₃+Al(C₂H₅)₃ have been determined. For chain transfer with ethylene and propylene these values are equal to 0.84 l/mol^–1 sec^–1 (80°C) and 0.04 l mol^–1 sec^–1 (70°C), respectively, and for chain transfer with hydrogen they amount to 23 l^1/2mol^–1/2sec^–1 (ethylene polymerization, 80°C) and 6 l^1/2 mol^–1/2sec (propylene polymerization, 70°C).

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-TiCl₃·0.3 AlCl³+Al(C₂H₅)₃. 0,84 ^{–1 –1} (80°) 0,04 ^{–1 –1} (70°), 23 ^{1/2 –1/2 –1} ( , 80°) 6 ^{1/2 –1/2} ( , 70°).

     

Formation of hexagonal MoO3 upon the decomposition of silica-supported ammonium paramolybdate

Upon the decomposition of silica-supported ammonium paramolybdate, hexagonal MoO₃ is formed at 300–350 °C. Irreversible transformation of hexagonal to rhombic MoO₃ is observed with increasing calcination temperature. The hexagonal MoO₃ structure is probably stabilized by the insertion of ammonium and silicon ions into the lattice of molybdenum trioxide.

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, , 300–359 °C . MoO₃ . MoO₃, , MoO₃.

     

Kinetic studies of methanethiol disproportionation

Kinetic regularities in catalytic disproportionation of methanethiol to dimethyl sulfide and hydrogen sulfide have been studied in a flow circulation reactor. A kinetic equation is suggested to describe the reaction on inhomogeneous surfaces.

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- - . , .

     

Interpretation of energy stability for Ti27+ and Ti26+ dimers

By using the interacting bonds method (IBM), it has been established that for the chloride Ziegler systems (TiCl₄+AlR₃) for polymerization the formation of Ti ₂ ⁷⁺ and Ti ₂ ⁶⁺ pairs is a thermodynamically favorable process.

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(TiCl₄+AlR₃) () , Ti ₂ ⁷⁺ Ti ₂ ⁶⁺ .

     

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^–]. .

     

Studies of calcium orthosilicate polymorphism by differential thermal analysis

The polymorphic transitions of calcium orthosilicate have been studied by means of differential thermal analysis. The parameters of-Ca₂SiO₄ synthesis without stabilizers haye been established.

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Zusammenfassung Mittels DTA wurden die Polymorphieübergänge von Kalziumorthosilikat untersucht. Die Parameter zur Synthese von-Ca₂SiO₄ ohne Stabilisatoren wurden bestimmt.

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- . - -Ca₂SiO₄ .