The effect of the conditions for the preparation of iron oxide nanoparticles on their catalytic characteristics in the oxidation of CO

The catalytic characteristics of systems prepared by mechanically mixing iron oxide nanoparticles, produced in the thermolysis of carboxylate complexes at 300–750°C, with aluminum oxide in the oxidation of CO were studied. It was shown that increase in the size of the iron oxide nanoparticles leads to decrease in the catalytic activity of the samples as a result of their different structural and textural characteristics, which change in relation to the synthesis conditions. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 300–305, September–October, 2006.     

Influence of preparation procedure on the surface chemistry and catalytic characteristics of FeZSM-5 zeolite in selective oxidation of benzene to phenol

The influence of preparation procedure on the nature of active centers, surface chemistry, and catalytic characteristics of FeZSM-5 zeolite in selective oxidation of benzene to phenol using N₂O as an oxidizing agent was studied.     

Solvent effect on molecular characteristics of polybutadiene and on the kinetic heterogeneity of catalytic systems based on TiCl4

Solvent effect on the molecular characteristics of polybutadiene and on the kinetic heterogeneity of catalytic systems based on TiCl₄ was studied.     

The effect of synthesis procedure on the catalytic performance of isostructural ZIF‐8

We demonstrate the synthesis of isostructural zeolitic imidazole framework (ZIF‐8) using four distinct synthetic methods. Subsequently, the variations in physicochemical properties were analyzed through the catalytic reaction of CO₂ cycloaddition of epoxide. It was thus demonstrated that simply by changing the type of synthetic method for the preparation of ZIF‐8, the physicochemical properties were changed significantly which in turn influenced the catalytic activity of ZIF‐8. It was found that the synthetic method affected the crystal growth and consequently influenced the physicochemical properties which are crucial aspects in metal–organic framework applications. There is an almost exponential relationship between the reactivity of various ZIF‐8 samples in CO₂ cycloaddition of epoxide and the surface area, CO₂ adsorption and pore volume.     

The influence of the nature of surfactants and dispersion medium on the catalytic effect of reverse micellar systems

The catalytic effect of reverse micellar systems in alkaline hydrolysis of phosphonic acid esters is to a considerable extent determined by the structure of the substrate and surfactant and the nature of the oil phase but weakly depends on the surface potential of the aggregates. AOT-butanol-decane-water, sodium dodecyl sulfate-butanol-decane-water, and cetyltrimethylammonium bromide-butanol-decane-water microemulsions exhibit specific catalytic properties rather than catalytic properties intermediate between those of the surfactant-alkane-water and surfactant-alkanol-water three-component systems.     

The effect of the nature of hydrophilic ionic liquid on the catalytic activity of horseradish and soybean peroxidases

The kinetics of guaiacol oxidation by hydrogen peroxide and tert-butyl hydroperoxide catalyzed by horseradish and soybean peroxidases in the presence of 1-butyl-3-methylimidazolium acetate and tet-rafluoroborates of 1-butyl-3-methylimidazolium and N-butyl-4-methylpyridinium are studied and compared. The inhibiting effect of acetate ionic liquid on both peroxidases that occurred via the noncompetitive type is found; the Michaelis and inhibition constants have been calculated. Causes of different degrees of inhibition of the catalytic activity of plant peroxidases by ionic liquids are discussed. The advantages of their application compared to the polar molecular organic solvents are demonstrated.     

An efficient of Grignard-type procedure for the preparation of gem-diallylated compound

An efficient and a new procedure for the conversion of various carboxylic acid derivatives into the corresponding gem-diallylated compound under mild reaction condition has been developed. The triallylaluminum mediated Grignard-type addition of carboxylic acid derivative was utilized as a key operation to affect the transformation. The procedure is operationally simple, giving good to excellent product yields for a broad range of substrates. The chemoselectivity and regioselectivity of triallylaluminum were also demonstrated.     

The preparation and properties of 1,4-diazaphenoselenazine

The preparation and properties of 1,4-diazaphenoselenazine are described and compared with those of 1,4-diazaphenothiazine. Experiments leading to nitro and chloro derivatives and also ring-cleavage products of both the selenium and sulphur-containing heterocycles are also described.     

The nature of permeability anisotropy and catalytic activity

The phenomena of permeability anisotropy and an increase in the rates of catalytic reactions in porous membranes modified with highly dispersed catalytic systems were analyzed. A model of stochastic gas motions was proposed; this model is based on the hypothesis of the specific interaction of molecules with the inner surface of pores resulting in a nonisotropic distribution of molecules over traveling directions. The effects of asymmetric gas transfer in porous and gradient-porous membranes were considered to explain differences in the rates of heterogeneous catalytic reactions in a nanoporous membrane reactor under changes in the direction of supplying a reaction mixture. From the model proposed, it follows that the transversal diffusion of gas molecules is most probable in the porous medium of a ceramic membrane with a pore-size distribution gradient from large to small pores along the flow direction. This diffusion results in an increase in the frequency of molecular collisions with the wall of a microchannel and, correspondingly, in an increase in the contact time. The model proposed explains the intensification of a number of heterogeneous catalytic reactions performed in the porous media of catalytic porous membranes.     

Ni-SiW12／MCM-41催化剂的制备与催化性能研究

加氢转化是石油炼制工业中的一项重要工艺,近年来,随着石油工业对中间馏分油需求的持续增长和环保要求的日益苛刻,加氢转化技术面临着巨大挑战。目前对C6以下正构庚烷异构化反应的研究较多,对庚烷等长链正构烷烃异构化研究在国外已有报道,在国内对长链烷烃异构化的研究刚处于起     

Semi-automatic catalytic titrations based on the 1,4-dihydroxyphthalimide dioxime/iodate/nickel system

Summary A new system, in which the nickel-catalysed oxidation of 1,4-dihydroxyphthalimide dioxime by iodate as the indicator reaction, is described. This system can be used for semi-automatic titration of aminopolycarboxylic acids because of their inhibitory effect on the indicator reaction. Amounts of EDTA and DCTA in the range 700–6000g were determined with an error of about 1%. The method has also been used for the indirect catalytic titrimetric determination of Ni(II), Hg(II) and Fe(III) with good results.

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Zusammenfassung Die von Nickel katalysierte Oxydation von 1,4-Dihydroxyphthalimiddioxim durch Jodat wird als neue Indikator-Reaktion beschrieben. Sie kann für die halbautomatische Titration von Aminopolycarbonsäuren wegen deren Hinderungseffekt auf diese Reaktion verwendet werden. Mengen von 700 bis 6000 g ÄDTA und DCTA wurden mit einem Fehler von etwa 1% bestimmt. Außerdem wurde die Reaktion für die indirekte katalytische Titration von Ni(II), Hg(II) und Fe(III) mit gutem Erfolg angewendet.

     

The nature and function of the catalytic centres of the DMSO reductases

Density functional theory calculations have been performed to probe aspects of the function of the reaction centres of the DMSO reductase enzymes, in respect of catalysis of oxygen atom transfer (OAT). The first comparison between Mo and W at the active site of these enzymes has been accomplished by a consideration of the reaction profile for OAT from DMSO to [MoIV(OMe)(S2C2H2)2]1- versus that for the corresponding reaction with [WIV(OMe)(S2C2H2)2]1-. Both reaction profiles involve two transition states separated by a well-defined intermediate; however, whilst the second transition state (TS2) is clearly rate-limiting for the Mo system, the two transition states have a similar energy for the W system. The activation energy for OAT from DMSO to [WIV(OMe)(S2C2H2)2]1- is ca. 23 kJ mol-1 lower for the corresponding reaction with Mo, consistent with the significantly faster rate of reduction of DMSO by Rhodobacter capsulatus W-DMSO reductase than by its Mo counterpart. Consistent with the principle of the entatic state, the geometrical constraints imposed by the protein on the metal centre of the Mo- and W-DMSO reductases facilitate OAT by favouring a trigonal prismatic geometry for the transition state TS2 that is close to that observed for the metal in the oxidised form of each of these enzymes. The effects of different tautomers of a simplified form of the pyran ring-opened, dihydropterin state of the molybdopterin cofactor on the reaction profile for OAT have been considered. The major effect, a significant lowering of the activation barrier associated with TS2, is observed for a protonated form of a tautomer that involves conjugation between the pyrazine and metallodithiolene rings.     

Improved etherification procedure for the preparation of dibenz[b,f][1,4]oxazepine

The effect of temperature and catalyst on the yield and rate of the etherification reaction between 1 and 2 was investigated and alternative methods for separation of 3 and 4 from the reaction mixture have been described.     

Effect of the catalyst nature and quantity on catalytic olefination

The study of the catalyst nature effect on the catalytic olefination of 4-chlorobenzaldehyde hydrazone by polyhaloalkanes revealed that the best catalysts for the reaction are copper salts. With polyhaloalkanes more active than CCl₄, like CBr₄ and CCl₃Br, the olefination can proceed without catalyst.     

The nature of the indenyl effect

The eta(5)-to-eta(3) coordination shift of cyclopentadienyl (Cp=C(5)H(5)(-)) and indenyl (Ind=C(9)H(7)(-)) ligands in molybdenocene complexes, [(eta(5)-Cp')(eta(5)-Cp)Mo(CO)(2)](2+) (Cp'=Cp or Ind), driven by a two-electron reduction of those species, was studied and compared by means of molecular orbital calculations (B3LYP HF/DFT hybrid functional, DZP basis sets). The results obtained, in terms of optimized geometries, relative energies, and bond analysis parameters, compare well with the experimental data, and verify the well-known indenyl effect, that is, a significantly more facile eta(5)-to-eta(3) rearrangement for the indenyl ligand when compared to cyclopentadienyl. However, the study of the folding of free Cp and Ind, combined with the (eta(5/3)-Cp')-M bond analysis, shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand, such as the traditionally accepted aromaticity gain in the benzene ring formed in eta(3)-Ind complexes. Instead, it is directly related to the Cp'-M bond strength. While the difference in the energy required to fold the two free ligands is negligible (< or =1 kcal mol(-1) for folding angles up to 20 degrees), the (eta(5)-Cp)-M bond is stronger than that of (eta(5)-Ind)-M; however, the opposite situation is found for the eta(3) coordination mode. The net result, for Cp'=Ind, is a destabilization of the eta(5) complexes and a stabilization of the eta(3) intermediates or transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step.     

Influence of the molecular structure and the nature of the solvent on the absorption and fluorescence characteristics of rhodamines

A study of the equilibrium of the molecular forms of rhodamine 19 in aqueous and ethanolic solution is carried out by determining the absorption and fluorescence characteristics of the zwitterionic and the cationic forms of the dye. The optical properties of rhodamine 19 are compared with those obtained for rhodamine 6G and also with those previously reported for rhodamine 3B and for the molecular forms of rhodamine B in water and ethanol. Different aspects of the molecular structure of the rhodamines and solvent effects are discussed, as well as their influence on the photophysical properties of the rhodamines. The aggregation of the molecular forms of rhodamine 19 is also studied in water and ethanol.     

An efficient and improved procedure for preparation of triflyl azide and application in catalytic diazotransfer reaction

An efficient and improved procedure for preparation of triflyl azide and application in catalytic diazotransfer reaction are described. The amount of highly toxic reagents NaN₃ and Tf₂O, is significantly reduced comparing with the previous protocol.     

Solvent effect on catalytic properties of the HCI-DMF-1,1,2,2-tetrachloroethane system

Ionization of 2- and 3-nitroanilines was studied in HCl-DMF-1,1,2,2-tetrachloro-ethane (TCE) solutions at 25 °C. The ionization capability of the medium and basicity constants pK _i of indicators change depending on the ratio of the components. The numerical values of pK _i are found to depend on the analytical composition of the DMF-TCE solvent. The solvent effect on pK _i is associated with a change in the solvation of the nonionized form of the indicators.Translanted fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1446–1449, June, 1996.