Home About us Contact
|
Home About us Contact | ||
|
|
||
Various Reaction Parameters (various + reaction_parameter)
Selected AbstractsLewis Basic Ionic Liquids-Catalyzed Conversion of Carbon Dioxide to Cyclic CarbonatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Zhen-Zhen Yang Abstract A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed. [source] Metal-Free and Copper-Promoted Single-Pot Hydrocarboxylation of Cycloalkanes to Carboxylic Acids in Aqueous MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Marina Abstract A simple and effective method for the transformation, under mild conditions and in aqueous medium, of various cycloalkanes (cyclopentane, cyclohexane, methylcyclohexane, cis - and trans -1,2-dimethylcyclohexane, cycloheptane, cyclooctane and adamantane) into the corresponding cycloalkanecarboxylic acids bearing one more carbon atom, is achieved. This method is characterized by a single-pot, low-temperature hydrocarboxylation reaction of the cycloalkane with carbon monoxide, water and potassium peroxodisulfate in water/acetonitrile medium, proceeding either in the absence or in the presence of a metal promoter. The influence of various reaction parameters, such as type and amount of metal promoter, solvent composition, temperature, time, carbon monoxide pressure, oxidant and cycloalkane, is investigated, leading to an optimization of the cyclohexane and cyclopentane carboxylations. The highest efficiency is observed in the systems promoted by a tetracopper(II) triethanolaminate-derived complex, which also shows different bond and stereoselectivity parameters (compared to the metal-free systems) in the carboxylations of methylcyclohexane and stereoisomeric 1,2-dimethylcyclohexanes. A free radical mechanism is proposed for the carboxylation of cyclohexane as a model substrate, involving the formation of an acyl radical, its oxidation and consequent hydroxylation by water. Relevant features of the present hydrocarboxylation method, besides the operation in aqueous medium, include the exceptional metal-free and acid-solvent-free reaction conditions, a rare hydroxylating role of water, substrate versatility, low temperatures (ca. 50,°C) and a rather high efficiency (up to 72% carboxylic acid yields based on cycloalkane). [source] Miniemulsion polymerization of a fluorinated acrylate copolymer: Kinetic studies and nanolatex morphology characterizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Qinghua Zhang Abstract A stable fluoroacrylate copolymer emulsion was successfully prepared by miniemulsion polymerization with fluoroacrylate, lauryl methylacrylate, and methyl methacrylate as monomers. Extremely hydrophobic fluoroacrylate, instead of conventional cosurfactants, was used as a reactive cosurfactant to stabilize the miniemulsions. The results indicated that fluoroacrylate retarded Ostwald ripening and allowed the production of stable miniemulsions. The chemical compositions of the copolymer were studied with Fourier transform infrared and 1H-NMR. The average composition of the copolymers prepared with miniemulsions was in good agreement with the feed ratio according to 1H-NMR from the integration ratios corresponding to typical protons of the individual monomers. The particle size distribution and morphology of the latex particles were determined with laser particle analysis and transmission electron microscopy. The particle size of the latex underwent no change in the process of miniemulsion polymerization, but the particle size distributions were broader than those of conventional emulsion polymerization. The effects of various reaction parameters, including the temperature and concentrations of the emulsifier and initiator, on the miniemulsion polymerization were also investigated, and the polymerization rate and conversion increased with increasing concentrations of nonylphenol polyethoxylate (with an average of 40 ethylene oxide units per molecule), cetyltrimethylammonium, and 2,2,-azobisisobutyronitrile. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 641,647, 2007 [source] Study of Laser-Induced Photopolymerizations by Optical PyrometryMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 15 2004Patrick Lin Abstract Summary: Studies of the 355 nm laser induced free radical and cationic photopolymerization reactions of mono- and multifunctional monomers were conducted. These investigations were carried out with the aid of a specially constructed optical pyrometry instrument that provides rapid, reproducible temperature versus time profiles for these fast photopolymerization reactions. Using this technique, the effects of various reaction parameters and monomer structures on the rate and extent of the photopolymerization reactions were examined. Optical pyrometry instrument for the monitoring of laser-induced photopolymerizations. [source] Self and nonself recognition of chiral catalysts: The origin of nonlinear effects in the amino-alcohol catalyzed asymmetric addition of diorganozincs to aldehydesTHE CHEMICAL RECORD, Issue 2 2001Ryoji Noyori Abstract Asymmetric addition of dialkylzincs to aldehydes in the presence of (2S)-3- exo -(dimethylamino)isoborneol [(S)-DAIB] exhibits various nonclassical phenomena. The enantiomeric excess (ee) of the alkylation product, obtained with partially resolved DAIB, is much higher than that of the chiral amino alcohol, while the rate decreases considerably as the ee of DAIB is lowered. The asymmetric amplification effects reflect the relative turnover numbers of two enantiomorphic catalytic cycles, where an essential feature is the reversible homochiral and heterochiral dimerization of the coexisting enantiomeric DAIB-based Zn catalysts. The interplay between the thermodynamics of the monomer/dimer equilibration and the kinetics of alkylation reaction strongly affect the overall profile of asymmetric catalysis. The self and nonself recognition of the chiral Zn catalysts is a general phenomenon when (S)-DAIB is mixed with its enantiomer, diastereomer, or even an achiral ,-amino alcohol. The degree of nonlinearity is highly affected not only by the structures and purity of catalysts but also by various reaction parameters. The salient features have been clarified on the basis of molecular weight measurements, NMR and X-ray crystallographic studies of organozinc complexes, and kinetic experiments, as well as computer-aided quantitative analysis. © 2001 John Wiley & Sons, Inc. and The Japan Chemical Journal Forum Chem Rec 1:85,100, 2001 [source] Modellierung und Simulation von Chemiereaktoren , Aspekte einer zeitgemäßen IngenieurausbildungCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 1-2 2005J. Hagen Prof. Abstract Die Durchführung chemischer Prozesse in der Technik unter möglichst optimalen Bedingungen setzt ein Grundverständnis für die Arbeitsweise von Chemiereaktoren voraus. Grundlage der Modellierung von Chemiereaktoren sind die Stoff- und Wärmebilanz und die Kinetik der Reaktion. Nur in einfachen Fällen lassen sich analytische Lösungen für Problemstellungen aus der Praxis durch Integration der Differentialgleichungen finden. Das in der Chemieingenieurausbildung eingesetzte Softwarepaket POLYMATH ist sehr anwenderfreundlich und einfach zu erlernen. Es wird u.,a. eingesetzt, um gekoppelte Differentialgleichungen simultan zu lösen und Datenanalyse durch Regression durchzuführen. Mit einem einmal aufgestellten Modell lässt sich der Einfluss verschiedener Reaktionsparameter auf den Gesamtprozess leicht nachvollziehbar simulieren. Modeling and Simulation of Chemical Reactors , Aspects of a Modern Education of Engineers Understanding how chemical reactors work lies at the heart of almost every chemical processing operation. Basis information for modeling and simulation of chemical reactors is needed from mass transfer, heat transfer and chemical kinetics. Only simple problems from practice can be solved analytically by means of integration of the differential equations. POLYMATH is a extremely user-friendly software package which makes modeling easy for the education of chemical engineers and chemists. POLYMATH is used to numerically solve coupled differential equations simultaneously or to find kinetic parameters in rate expressions by regression. Using an identified model the influence of various reaction parameters on the overall process can be simulated easily. [source] | |||||||||||||