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Homogeneous Conditions (homogeneous + condition)
Selected AbstractsChemInform Abstract: Synthesis of Some Electron-Rich Aryl(hetaryl)oxiranes under Phase-Transfer and Homogeneous Conditions.CHEMINFORM, Issue 27 2009A. A. Afon'kin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Improved Suzuki,Miyaura Reactions of Aryldiazonium Salts with Boronic Acids by Tuning Palladium on Charcoal Catalyst PropertiesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009François-Xavier Felpin Abstract An improved Suzuki,Miyaura cross-coupling reaction of aryldiazonium tetrafluoroborates with boronic acids catalyzed by a highly active palladium catalyst supported on charcoal is described as an extremely practical and efficient protocol. A properties-activity study of various catalysts clearly established that the optimal catalytic activity was obtained with palladium nanoparticles having a low oxidation degree and uniformly dispersed on the charcoal. The optimized reaction conditions allow the cross-coupling to proceed at room temperature without any base and ligand in technical grade methanol. Although the catalyst could not be recycled, the low palladium contamination of the solvent and product after a simple filtration of the palladium on charcoal (Pd/C) renders the present protocol competitive and safer for the environment compared to more conventional homogeneous conditions. We have highlighted the efficiency of this novel protocol by a short synthesis of the fungicide Boscalid®. [source] Efficient and Practical Cross-Coupling of Arenediazonium Tetrafluoroborate Salts with Boronic Acids Catalyzed by Palladium(0)/Barium CarbonateADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2008François-Xavier Felpin Abstract The cross-coupling reaction of arenediazonium tetrafluoroborate salts with boronic acids catalyzed by the unusual palladium(0)/barium carbonate catalyst is described as an extremely practical and highly efficient alternative to classical homogeneous conditions. Reactions are conducted under mild conditions at room temperature without any base and ligand. The opportunity of preparing unsymmetrical terphenyls in a one-pot process is also demonstrated. Finally, the power of this methodology is highlighted by the synthesis of Bifenazate. [source] Cationic Carboxylato Complexes of Dirhodium(II) with Oxo Thioethers: Catalysts for Silane Alcoholysis under Homogeneous and Liquid-Liquid Biphasic ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2007Andrea Biffis Abstract A set of cationic dirhodium(II) complexes with oxo thioethers was prepared and employed as catalysts for the silane alcoholysis reaction. The complexes were found to be highly active under homogeneous conditions, both in the absence and in the presence of a solvent, including coordinating solvents such as N,N -dimethylformamide; the catalysts could be conveniently employed in concentrations as low as 0.01 mol,%, and a maximum TON of 30000 was recorded after 24,h. The same catalysts were also employed under liquid-liquid biphasic conditions with an ionic liquid as the catalyst-containing phase: comparable catalytic activity was observed under these conditions, and the catalyst-containing phase could be recovered and recycled. A chiral cationic dirhodium(II) complex was also prepared in the frame of this work; kinetic resolution of a racemic alcohol was attempted with this catalyst, unfortunately without success. [source] Cyclohexene hydrogenation using Group VIII metal complexes as catalysts in heterogeneous and homogeneous conditionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2001E Quiroga Abstract The stability and catalytic behaviour of a ruthenium complex with chloride and tridecylamine as ligands were studied. The hydrogenation of cyclohexene carried out in mild conditions, both in homogeneous and heterogeneous conditions, was used as a test reaction. FTIR and XPS results show that the active species is the complex itself, which is stable under the reaction conditions. XPS determination shows that the ruthenium complex is tetra-coordinated, suggesting that its formula is [RuCl2(NH2(CH2)12CH3)2]. This ruthenium complex supported on ,-Al2O3 is more active and sulfur-resistant than the same complex unsupported and even more than a nickel complex with the above mentioned ligands. The Ru complex, supported or not, is also more active and sulfur-resistant than a conventional Ru/,-Al2O3 catalyst evaluated in the same operational conditions. © 2001 Society of Chemical Industry [source] Complete dissolution and hydrolysis of wood in hot waterAICHE JOURNAL, Issue 10 2008Zhen Fang Abstract When willow and water were heated rapidly (7,16°C/s) to high temperatures and high pressures, most of willow (90 vol %) dissolved in water at 341°C in 2.5 s without complete dissolution. Adding 0.8 wt % Na2CO3, complete dissolution of willow (concentration up to 35 vol %) was observed at 329,367°C and water densities of 322,787 kg/m3 (14,106 MPa) in 1.5 s. By cooling the solublized willow immediately, micron particles were obtained via precipitation. If heated further to 400°C, willow was completely hydrolyzed to sugars/sugar oligomers in 14.6 s at homogeneous conditions. A flow reactor was proposed to completely solubilize willow for the production of micron particles, sugars, bio-fuels and chemicals continuously. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Radical clocks and electron transfer.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2005Comparison of crown ether effects on the reactivity of potassium, magnesium towards 1-bromo-2-(3-butenyl)benzene. Abstract The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis -dicyclohexano-18-crown-6 or tert -butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia,33% tert -butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal,solution interface. More specifically, the non-observation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright © 2005 John Wiley & Sons, Ltd. [source] Controlled radical polymerization of 2-hydroxyethyl methacrylate with a hydrophilic ruthenium complex and the synthesis of amphiphilic random and block copolymers with methyl methacrylate,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2002Yusuke Fuji Abstract A hydrophilic ruthenium complex with ionic phosphine ligands {1: RuCl2[P(3-C6H4SO3Na)(C6H5)2]2} induced controlled radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in methanol under homogeneous conditions; the initiator was a chloride (R-Cl) such as CHCl2COPh. The number-average molecular weights of poly(HEMA) increased in direct proportion to monomer conversion, and the molecular weight distributions were relatively narrow (Mw/Mn = 1.4,1.7). A similar living radical polymerization was possible with (MMA)2 -Cl [(CH3)2C(CO2CH3)CH2C(CH3)(CO2CH3)Cl] as an initiator coupled with amine additives such as n -Bu3N. In a similar homogeneous system in methanol, methyl methacrylate (MMA) could also be polymerized in living fashion with the R-Cl/1 initiating system. Especially for such hydrophobic polymers, the water-soluble ruthenium catalyst was readily removed from the polymers by simple washing with an aqueous dilute acid. This system can be applied to the direct synthesis of amphiphilic random and block copolymers of HEMA and MMA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2055,2065, 2002 [source] Blocking Two-level Factorial ExperimentsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2007Murat Kulahci Abstract Blocking is commonly used in experimental design to eliminate unwanted variation by creating more homogeneous conditions for experimental treatments within each block. While it has been a standard practice in experimental design, blocking fractional factorials still presents many challenges due to differences between treatment and blocking variables. Lately, new design criteria such as the total number of clear effects and fractional resolution have been proposed to design blocked two-level fractional factorial experiments. This article presents a flexible matrix representation for two-level fractional factorials that will allow experimenters and software developers to block such experiments based on any design criterion that is suitable with the experimental conditions. Copyright © 2006 John Wiley & Sons, Ltd. [source] Measurement of Homogeneous Kinase Activity for Cell Lysates Based on the Aggregation of Gold NanoparticlesCHEMBIOCHEM, Issue 8 2007Jun Oishi When the charge sticks. A kinase activity screening system based on the aggregation of gold nanoparticles induced by cationic substrate peptides as coagulants has been constructed. The system can conduct and monitor kinase reactions under homogeneous conditions and has been successfully applied to the kinase assay of cell lysates. [source] Modeling of Particle Layer Detachment under Consideration of Transient Kinetic EffectsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2010Q. Zhang Abstract Particle layers tend to build up on walls in many filtration and separation processes, calling for periodic removal in order to keep the device running. Important factors are the adhesion of the layer on the substrate and the cohesion of the particles in the layer. Models describing such layer detachment generally assume constant and homogeneous conditions for the forces acting on the layer. But in reality detachment is extremely nonstationary concerning place and time, primarily due to changing conditions for the forces on the one hand and changes in the particle layer morphology on the other. This paper describes a model and a simulation considering such transient kinetic effects on filter cake detachment. Diverse computing results are presented and discussed. [source] Tuning of Electronic Properties of Single-Walled Carbon Nanotubes under Homogenous ConditionsCHEMPHYSCHEM, Issue 6 2009Yutaka Maeda Prof. Abstract Reversible and non-bonding interaction between SWNTs and ODCB is observed from the analyses of visible near-infrared absorption data and Raman spectroscopies (see spectra). The solvent effect on SWNTs effectively controls the electronic structure of SWNTs under homogeneous conditions. The dispersion of single-walled carbon nanotubes (SWNTs) in o -dichlorobenzene (ODCB) is studied. Reversible and non-bonding interaction between SWNTs and ODCB is observed from the analyses of visible near-infrared (Vis-NIR) absorption data and Raman spectroscopy. This interaction should be one of the important factors for stable dispersion of SWNTs in ODCB. The solvent effect on SWNTs effectively controls the electronic structure of SWNTs under homogeneous conditions. [source] Alkyne Hydroarylation in Ionic Liquids Catalyzed by Palladium(II) ComplexesCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 7 2010Andrea Biffis Dr. Abstract The efficiency of dicarbene palladium(II) complexes and of simple palladium(II) acetate as catalysts for alkyne hydroarylation under liquid-liquid biphasic conditions involving an ionic liquid as the catalyst-containing phase is investigated. The results obtained under these conditions, both in terms of activity and selectivity, are compared with those previously obtained under homogeneous conditions. The catalytic efficiency of the systems is found to be markedly dependent on the nature of the anion of the ionic liquid. Suitable anions are found to significantly improve the catalytic performance in comparison to homogeneous conditions. Preliminary investigations on the recyclability of the system as well as the on advantages of using an acidic ionic liquid are also carried out. 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