NMR study of the stoichiometry,stability and exchange kinetics of complexation reaction between Pb2+ ion and 18-crown-6 in binary acetonitrile-water mixtures

Proton NMR was used to study the complexation reaction between lead ion and 18-crown-6 in a number of binary acetonitrile-water mixtures. Formation constant for the resulting 11 complexes in different solvent mixtures was determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and amount of water in the mixed solvent. The dissociative kinetics of the complex was studied by proton line-shape analysis. The Arrhenius plots showed a distinct isokinetic temperature at about 25°C at which the decomplexation rate is more or less independent of the solvent composition. the complexation rate and the activation parameters E _a , H and S, for the exchange have been determined and found to be strongly solvent dependent. There is actually a linear relationship between the mole fraction of acetonitrile in the mixed solvent and logarithm of the stability constant as well as activation parameters.     

Effect of homogeneous initiator on heterogeneous-homogeneous oxidation of methane

A kinetic method of freezing out free radicals combined with recording ESR spectra was used to study the HCl effect on the partial oxidation of methane over SiO₂. This effect is ascribed to the surface modification of catalyst.

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HCl SiO₂. .

     

Rate constants for photochemically induced hydrogen abstraction calculated from spin trapping rates

ESR spin trapping method has been applied to calculate the rate constant for -hydrogen abstraction from ethylbenzene by triplet anthraquinone: k₁=1.1×10⁷ M^–1 s^–1 (error of estimation 25%).

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( ) -CH : k₁=1.1×10⁷ M^–1–1 ( 25%)

     

Thermal dissociation of basic aluminium ammonium sulfate in vacuum

A mathematical model of the thermal decomposition of basic aluminium ammonium sulfate has been developed. The construction of the model consisted in simulation of TG and DTG curves, with the use of kinetic parameters identified on the basis of results obtained in measurements of the rate of thermal dissociation of the compound under isothermal and non-isothermal conditions.

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Zusammenfassung Es wurde das mathematische Modell fur thermische Zersetzung des basischen Ammoniumaluminiumsulfats bearbeitet. Die Struktur des Modells bestand in der Nachbildung von thermogravimetrischen Kurven TG, DTG mittels der kinetischen Parameter, die auf Grund der isothermen und der nichtisothermen Ergebnisse der Untersuchungen nach der Dissoziationsgeschwindigkeit von Verbindungen identifiziert wurden.

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Résumé Un modèle mathématique décrivant la décomposition thermique du sulfate basique d'aluminium et d'ammonium est présenté.La méthode consiste à simuler les courbes thermogravimétriques TG et TGD à l'aide des paramètres cinétiques identifiés sur la base des résultats des déterminations isothermes et nonisothermes de la vitesse de la dissociation du composé.

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. , , .

     

Influence of oxygen compound structural elements of stretching vibration frequency of surface hydroxy groups

Stretching vibration frequencies of OH groups ( OH) in acidic oxygen compounds are determined by the electrostatic characteristics (E_p) of the polyhedron containing this group. Empirical dependence of OH various hydroxy groups on the number and nature of their binding cations is suggested.

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, OH- ( OH) (). .

     

Solvent effects on the initial and transition states for the solvolysis of trans-dichlorobis-(N-methylethylenediamine) cobalt(III) complex in water–dimethyl sulfoxide mixtures

Solvent effects on the initial and transition states for the solvolysis of the trans-dichlorobis-(N-methylethylenediamine)cobalt(III), (meen), complex have been investigated in the 25–55 °C range in aqueous DMSO mixtures, of varying solvent composition up to 60% by vol. The log of the first order rate constant, k, varies non-linearly with the reciprocal of the dielectric constant at the same temperature, due to differential solvation of the initial and transition states. The changes in the enthalpy, H , and entropy, S , of activation with the mole fraction of the co-solvent show extrema at the composition range where the change in solvent structure occurs. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the effect of solvent structure on the complex ion in the transition state dominates the initial state and that this effect increases as the mole fraction of co-solvent increases.     

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 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.

     

Surface redox properties of Rh/AlPO4 and Rh/AlPO4?SiO2 catalysts

Electron donor and acceptor properties of AlPO₄ and AlPO₄–SiO₂ (2080 wt. %) supported rhodium catalysts have been studied. It was observed that the effect of metal deposition on both electron acceptor and donor properties depend on the support and precipitation agent. AlPO₄ supported rhodium showed better acoeptor than donor properties, while for Rh/AlPO₄–SiO₂, the acceptor properties were superior. However, the effect of metal on the redox properties is slight.

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AlPO₄ QlPO₄ SiO₂ (2080 .%). ]ye . AlPO₄ , , Rh/AlPO₄–SiO₂ . , - .

     

The mechanism of thermal decomposition of Co(NO3)2 · 2H2O

The mechanism of thermal decomposition of Co(NO₃)₂ · 2H₂O was found to involve stages in which Co(NO₃)₃ and Co₂O₃ · H₂O are formed both of which decompose to Co₃O₄. During the process, the total cobalt enters the +3 oxidation state, which is consistent with the results reported by Mehandjiev [2].

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Zusammenfassung Es wurde gefunden, daß der Zersetzungsmechanismus von Co(NO₃)₂ · 2H₂O Schritte umfaßt, bei denen Co(NO₃)₃ sowie Co₂O₃ · H₂O gebildet werden, beides weiterzerfallend zu Co₃O₄. Während des Vorganges erreicht das Gesamtkobalt die Oxidationsstufe +3, was mit Ergebnissen von Mehandjiev übereinstimmt [2].

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, , CO₃O₄. , .

     

UV-VIS spectroscopic study of interaction and transformation of allyl alcohol on zeolites HZSM-5

Formation of alkenylcarbenium ions has been proved during transformation of allyl alcohol on zeolite HZSM-5.

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HZSM-5.

     

Study of hydroisomerization of n-hexane on natural mordenite catalyst

A mordenite-containing rock sample from the Tokaj Mountains (Hungary) and its various forms modified by chemical treatment have been tested for catalytic properties during isomerization of n-hexane. Addition of Pt to the catalyst leads to a sharp decrease in the rate of cracking and in the rate of deactivation and this results in a catalyst of high selectivity for hexane isomers.

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(), , , , -. Pt , .

     

Poissonian stationary distribution in a class of detailed balanced reactions

We investigate those detailed balanced (vectorial) complex chemical reactions that belong to the class of simple Markovian population processes and show that there is no chemical reaction with independent reaction rates having a Poissonian stationary distribution. There exists, however, a manifold of reactions with dependent (as given) reaction rates and with Poissonian stationary distribution.

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() , , , . , () .

     

Kinetics of carbonyl triplet reactions in water

The presence of urea during the gelling of AlPO₄–Al₂O₃ catalysts (AlPO₄/Al₂O₃ weight ratio =3) has been studied with respect to its effect on the porous texture and surface acidity of the resulting gels. An increase in pore volume and mean pore radius with no modification in surface acidity is found when the AlPO₄–Al₂O₃ catalyst is modified by the addition of 5 mol% urea in the AlPO₄ solution.

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, AlPO₄/Al₂O₃ ( AlPO₄/Al₂O₃=3) . , AlPO₄/Al₂O₃ 5 .% AlPO₄ - .

     

Nonempirical calculations of water adsorption on bridged structural fragments of aluminosilicate

Within the discussion of the possibility to apply semiempirical methods for chemisorption calculations, nonempirical calculations of two types of adsorption complexes of H₂O molecule with bridged structural fragments of aluminosilicate have been carried out.

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, .

     

Effect of hydrothermal treatment on catalytic properties of superhigh-silica zeolites

The effect of hydrothermal treatment of decationized superhigh-silica zeolite on the mechanism of n-hexane conversion has been studied. It has been established that thermosteam modification sharply decreases the cracking activity and increases the selectivity to aromatization reactions. Zeolite acidity markedly decreases, but its crystal structure does not become amorphous.

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-. . .

     

Catalytic decomposition of N2O on La2Cu0.5M0.5O4 (M=Co, Ni, Cu and Zn)

Decomposition of N₂O has been studied over La₂Cu_0.5M_0.5O₄ (M=Co, Ni, Cu and Zn) between 380 and 485°C at 50 torr initial pressure of N₂O to understand the mutual interaction of two different active metal ions of the same concentration and valence in deciding the physico-chemical and catalytic properties. A multicenter type of adsorption of N₂O has been visualized and it is found that the rate is governed by the electronic factor.

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N₂O La₂Cu_0,5M_0,5O₄ (M=Co, Ni, Cu Zn) 380–485°C N₂O, 50 . , - . N₂O. .

     

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) . , . . , . . , .

     

Poly(vinylpyridine) complexes of palladium as hydrogenation catalysts. Effect of polymeric ligand structure

The title complexes exhibit high catalytic activity, selectivity and stability in hydrogenation of allyl alcohol. The structure of a polymeric ligand (i.e. the position of the nitrogen atom in the pyridine ring) affects catalyst activity. According to the hydrogenation rates of allyl alcohol, the complexes studied are arranged in the sequence: P4VP-Pd>P2VP-Pd>P2M5VP-Pd.

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, - - . ( ) . : 4->2-Pd>25-.