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Reaction Media (reaction + media)
Selected AbstractsAtom Transfer Carbonylation Using Ionic Liquids as Reaction Media.CHEMINFORM, Issue 19 2007Takahide Fukuyama 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, please click on HTML or PDF. [source] Ionic Liquid [omim][PF6] as an Efficient and Recyclable Reaction Media for the Cyanosilylation of Aldehydes Without Lewis Acid or Any Special Activation.CHEMINFORM, Issue 33 2005Zhi-Liang Shen Abstract For Abstract see ChemInform Abstract in Full Text. [source] Novel Potentiometric Sensors of Molecular Imprinted Polymers for Specific Binding of ChlormequatELECTROANALYSIS, Issue 2 2008Ayman Abstract Molecularly imprinted polymers (MIP) were used as potentiometric sensors for the selective recognition and determination of chlormequat (CMQ). They were produced after radical polymerization of 4-vinyl pyridine (4-VP) or methacrylic acid (MAA) monomers in the presence of a cross-linker. CMQ was used as template. Similar non-imprinted (NI) polymers (NIP) were produced by removing the template from reaction media. The effect of kind and amount of MIP or NIP sensors on the potentiometric behavior was investigated. Main analytical features were evaluated in steady and flow modes of operation. The sensor MIP/4-VP exhibited the best performance, presenting fast near-Nernstian response for CMQ over the concentration range 6.2×10,6,1.0×10,2,mol L,1 with detection limits of 4.1×10,6,mol L,1. The sensor was independent from the pH of test solutions in the range 5,10. Potentiometric selectivity coefficients of the proposed sensors were evaluated over several inorganic and organic cations. Results pointed out a good selectivity to CMQ. The sensor was applied to the potentiometric determination of CMQ in commercial phytopharmaceuticals and spiked water samples. Recoveries ranged 96 to 108.5%. [source] Synthesis and Characterization of Single-Crystalline Lanthanum Fluoride with a Ring-Like NanostructureEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2009Yang Tian Abstract LaF3 ring-like nanostructures with a diameter of less than 2 ,m have been fabricated by a facile, effective, and environmentally friendly molten salt synthesis route in which NaNO3 and KNO3 (2:1 molar ratio) act as reaction media and the rare-earth nitrate and NaF as precursor. X-ray diffraction, TEM, HR-TEM, energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy are all used to characterize the as-prepared samples. Experiments peformed with different reaction times indicate that a central-etching of the plates from the inner part towards the edge during nanocrystal growth plays a key role in the formation of LaF3 nanorings since no other templates/surfactants are present in our system. Additionally, the luminescence properties of LaF3 nanorings doped with Eu3+ cation have been investigated andcompared with those of bulk materials and nanoparticles with a size of approximately 50 nm. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Comparative Sol,Hydro(Solvo)thermal Synthesis of TiO2 NanocrystalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2006Xianfeng Yang Abstract Three small inorganic compounds [acetic acid (CH3COOH), nitric acid (HNO3), and hydrochloric acid (HCl)] andfive small organic compounds [n -butyl alcohol (CH3CH2CH2CH2OH), 1,2-propanediol (CH2OHCHOHCH3), propane-1,3-dicarboxylic acid (HOOCCH2COOH), butane-1,4-dicarboxylic acid (HOOCCH2CH2COOH), and ethylenediamine (H2NCH2CH2NH2)] with different donors (Cl,, NO3,, OH, COO,, and NH2) are used respectively and comparatively in different reaction media for tailoring the sol,hydrothermal synthesis of TiO2 nanocrystals at a specific reaction temperature and/or for different reaction times. Both anatase and rutile with a variety of nanostructures such as nanocubes, nanorods, nanoneedles, and their self-assembled nanospheres are selectively grown. Well-defined and crystalline anatase nanocrystals with a narrow size distribution are prepared in the presence of n -butyl alcohol. With the use of HCl, nanoneedles and their assembled nanospheres of phase-pure rutile are obtained under much less drastic conditions, even at 100 °C and for only two hours. The effects of the reaction media, synthesis temperatures, and aging times on the structures and shapes of the products are investigated in detail by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Catalysis by Ionic Liquids: Significant Rate Acceleration with the Use of [pmIm]Br in the Three-Component Synthesis of DithiocarbamatesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2008Brindaban C. Ranu Abstract An easily accessible neutral ionic liquid, 1-methyl-3-pentylimidazolium bromide, promoted a one-pot three-component condensation of an amine, carbon disulfide, and an activated alkene/dichloromethane/epoxide to produce the corresponding dithiocarbamates in high yields at room temperature. The reactions are very fast in ionic liquids relative to those in other reaction media. These reactions do not require any additional catalyst or solvent. The ionic liquid can be recovered and recycled for subsequent reactions. A plausible mechanism is suggested. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] SN2 Displacement by Bromide Ions in Dichloromethane , The Role of Reverse MicellesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006Lucia Brinchi Abstract Reverse micellar systems are of interest as reaction media because they are powerful models for biological compartmentalization, enzymatic catalysis and separation of biomolecules. Solutions of ionic surfactants in apolar solvents may contain reverse micelles, but they may also contain ion pairs, or small clusters, with waters of hydration. We studied the bimolecular reaction in CH2Cl2 solutions of cationic tetraalkylammonium bromide salts (onium salts), such as cetyltrimethylammonium bromide (CTABr), cetyltripropylammonium bromide (CTPABr) and tetra- n -butylammonium bromide (TBABr). Methylnaphthalene-2-sulfonate (,-MeONs), its 6-sulfonate derivative (,-MeONsS,) as the 2,6-lutidinium salt and methyl-5- N,N,N,trimethylammonium naphthalene-1-sulfonate (,-MeONsNT+) as the trifluoromethanesulfonate salt react with Br, in CH2Cl2. First-order rate constants, kobs, increase linearly and similarly for the three substrates with increasing concentrations of the onium salts. Reactions are faster with TBABr than they are with CTPABr and CTABr, and the reactivity of the three substrates is in the order: ,-MeONsNT+ >> ,-MeONsS, > ,-MeONs. The reactions are inhibited by the addition of H2O, but CTABr tolerates H2O in large excess. At [H2O]/[CTABr] = w0 , 6, "water-pool" reverse micelles form, and kobs for all three substrates is then independent of w0. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Intramolecular Opening of ,-Lactams with Amines as a Strategy Toward Enzymatically or Photochemically Triggered Activation of Lactenediyne ProdrugsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2003Luca Banfi Abstract In order to develop a general strategy for selective activation of designed enediyne prodrugs belonging to the "lactenediyne" family, we studied the scope of intramolecular transamidation of simple monocyclic ,-lactams bearing a tethered amine. The effect of substituents, of reaction media, and of the type of tether, on the rate of transamidation is disclosed. The possibility of triggering the transamidation event under mild conditions by the action of suitable enzymes or UV light was demonstrated on model monocyclic ,-lactams. Finally, the strategy of intramolecular opening of the ,-lactam leading to a larger seven-membered ring was employed on a lactenediyne, demonstrating that ring enlargement could unleash the reactivity of the enediyne moiety. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Ligand-Free and Heterogeneous Palladium on Carbon-Catalyzed Hetero-Suzuki,Miyaura Cross-CouplingADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Yoshiaki Kitamura Abstract A ligand-free and heterogeneous palladium on carbon (Pd/C)-catalyzed hetero-Suzuki,Miyaura coupling reaction has been developed. The protocol enables the construction of both heterocyclic-alicyclic and heterocyclic-heterocyclic biaryl derivatives in good to excellent yields. Furthermore, Pd/C could be reused. The time-course study clarified that palladium was leached into the reaction media as the reaction proceeded and then completely deposited on the carbon support. [source] Sharpless Asymmetric Dihydroxylation of Olefins in WaterSurfactant Media with Recycling of the Catalytic System by Membrane NanofiltrationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2008Abstract This paper presents a new and more sustainable alternative approach for the Sharpless catalytic asymmetric dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric dihydroxylation of 1-hexene in a 1.5,mM sodium cholate aqueous solution, using N -methylmorpholine N -oxide (NMO) as co-oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn-over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields. [source] The transient nature of maximum maleic anhydride grafting of polypropylene: A mechanistic approach based on a consecutive reaction model.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Abstract This article compares the batch solution and molten state chemical modification of an atactic polypropylene to yield a grafted polypropylene. Short reaction times appear to be sufficient and indeed necessary for the highest graft yields to be obtained if degradative processes occurring in both reaction media are to be avoided. The consecutive reactions for the optimized grafting reaction pathway were proposed for the solution process in an earlier article. The present work attempts to correlate this pathway with that of the molten state process. Grafted succinic anhydride groups react with two resorcine molecules to yield grafted succinyl-fluorescein groups. This work considers the resorcine units as true molecular probes, to be able to stabilize and activate the complexes formed between the succinic anhydride groups and the propylene sequence. This work shows the unsteady and later dynamic character of the process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 345,351, 2007 [source] Enhancement of activity and selectivity in lipase-catalyzed transesterification in ionic liquids by the use of additivesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2007Francisco J Hernández-Fernández Abstract BACKGROUND: Seven ionic liquids (ILs) based on 1-alkyl-3-methylimidazolium cation in combination with hexafluorophosphate and bis{(trifluoromethyl)sulfonyl}imide anions were tested as reaction media for lipase-catalyzed transesterification in low water conditions. With the aim of improving the activity and/or selectivity of the lipase, various treatments were applied to ionic liquid media such as equilibration with aqueous solutions of salts, NaHCO3 or Na2CO3, or the addition of a catalytic amount of a non-reactive organic base to the reaction mixture, triethylamine. RESULTS: The treated ionic liquids were shown to be excellent media for lipase-catalyzed ester synthesis by transesterification compared with conventional organic solvents, such as n -hexane. All treatments were found to enhance the synthetic activity of the enzyme, the best results being achieved with the addition of triethylamine. The addition of a catalytic amount of this base to the ILs resulted in a significant increase in both the synthetic activity and selectivity values. For instance, the synthetic activity in [emim+][TfN2,] was enhanced more than 12 times and the selectivity increased from 86% to 95% when triethylamine was used. CONCLUSION: These treatments could be easy-to-use approaches to improve the efficiency of enzymatic reactions in ionic liquids when the reaction does not proceed smoothly. Copyright © 2007 Society of Chemical Industry [source] Stochastic simulation of physicochemical processes performance over supported metal nanoparticlesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2008Evgenii V. Kovalyov Abstract The statistical lattice model has been proposed which permits one to take into account the change in the shape and surface morphology of the nanoparticle under the influence of the reaction media. The influence of monomolecular and dissociative adsorption on the particles equilibrium shape and surface morphology has been studied. It has been shown that by taking into account of attraction "adsorbate-metal" the reshaping of the initial hemispheric particle into cone-shaped one occurs induced by adsorption, similar to the experimentally observed reversible reshaping of active nanoparticles. The model reaction A+B2 has been studied taking into account the roughening of the active particle surface and the spillover phenomena of the adsorbed Aads species over the support surface. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] SUBCRITICAL WATER EXTRACTION OF CAFFEINE FROM BLACK TEA LEAF OF IRANJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2008ANVAR SHALMASHI ABSTRACT This study examines subcritical water extraction (SCWE) of caffeine from black tea leaf. The effects of various operating conditions such as water temperature (100, 125, 150 and 175C), water flow rate (1, 2 and 4 g/min), mean particle size (0.5, 1 and 2 mm) on extraction yield and rate were determined. SCWE at 175C, water flow rate of 2 g/min and mean particle size of 0.5 mm were found to be able to recover 3.82% (w/w) of caffeine present in the black tea leaf within 3 h of extraction. In comparison to the SCWE, conventional hot water extraction showed 3.30% (w/w) extraction yield. It was found also that pressure had no effect on extraction yield and rate. PRACTICAL APPLICATIONS Recently, subcritical water has become of great interest as an alternative solvent for extraction of natural active compounds. Subcritical water, as a green solvent, can be used in many different fields of applications. In recent years, extraction of flavors, fragrances and antioxidant components from plant materials, and hydrolysis of carbohydrates, vegetable oils and fatty acids have been widely investigated by many researchers. Using subcritical water for analytical purposes, for soil remediation and applying it as a reaction media are some other interesting fields for practical applications. Subcritical water is an excellent solvent for caffeine as well as many other organic compounds but is safer than the organic solvents that are used for caffeine extraction. [source] Poly(ethyleneglycol): A versatile and recyclable reaction medium in gaining access to benzo[4,5]imidazo[1,2- a]pyrimidines under microwave heatingJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2009Shu-Liang Wang Polyethylene glycol is found to be a nontoxic and recyclable reaction medium for the microwave-assisted, one-pot, multicomponent reactions of aromatic aldehydes with 2-aminobenzimidazole and 1,2-diphenylethanone in the presence of potassium carbonate. This environmentally friendly microwave protocol offers ease of operation and enables recyclability of reaction media and synthesis of a variety of substituted benzo[4,5]imidazo[1,2- a]pyrimidine derivatives. It is an efficient, promising, and green synthetic strategy to construct benzo[4,5]imidazo[1,2- a]pyrimidine skeleton. J. Heterocyclic Chem. (2009). [source] Advancement of Fischer-Tropsch synthesis via utilization of supercritical fluid reaction mediaAICHE JOURNAL, Issue 4 2010Nimir O. Elbashir Abstract The Fischer Tropsch Synthesis (FTS) reaction has been studied and for nearly a century for the production of fuels and chemicals from nonpetroleum sources. Research and utilization have occurred in both gas phase (fixed bed) and liquid phase (slurry bed) operation. The use of supercritical fluids as the reaction media for FTS (SCF-FTS) now has a 20-year history. Although a great deal of progress in SCF-FTS has been made on the lab scale, this process has yet to be expanded to pilot or industrial scale. This article reviews the research activities involving supercritical FTS and published in open literature from 1989 to 2008. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Conformation-dependent side reactions in interstrand-disulfide bridging of trimeric collagenous peptides by regioselective cysteine chemistryJOURNAL OF PEPTIDE SCIENCE, Issue 5 2002Barbara Saccá Abstract Conversion of single-chain or disulfide-bridged dimeric collagenous peptides into Cys(Npys) derivatives as activated species for subsequent regioselective thiol/disulfide exchange reactions leads to side products whose origin and nature was determined by HPLC and ESI-MS. In both cases the high tendency of the educts to self-associate into triple-helical homotrimers, as assessed by their dichroic properties in the reaction media, is responsible for the failure of this well established cysteine chemistry. Only by optimizing the synthetic strategy or by exploiting a kinetic control of the reaction, could these conformation-dependent limitations be more or less efficiently bypassed for the regioselective assembly of heterotrimeric collagen model peptides crosslinked with artificial cystine knots. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd. [source] Nucleophilic and acid catalyst behavior of a protic ionic liquid in a molecular reaction media.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2009Part Abstract This work presents a new approach using ionic liquids, namely ethylammonium nitrate. The aim was to analyze how the addition of small amounts of a protic ionic liquid to a pure molecular solvent, modifies the microscopic characteristics of a reaction medium. In order to achieve this, a kinetic study of nucleophilic aromatic substitution reactions between 1-fluoro-2,4-dinitrobenzene and 1-butylamine or piperidine was developed in this type of binary mixtures. We have detected nucleophiles competition originated by the presence of the ionic solvent at very low concentrations, observing the ethylamine derivative as the main substitution product. Moreover, in the light of previous results we have confirmed that the protic ionic liquid can act as both Brönsted acid and/or nucleophile. In this connection, we have selected the nucleophilic addition of amines to carbonyl compounds as reaction model. The protic ionic liquid in the presence of aromatic aldehydes substituted by electron-donating groups makes possible the formation of the corresponding imines with good yields. The results demonstrated that the influence of the protic ionic liquid is very important in the course of both reaction systems. Copyright © 2008 John Wiley & Sons, Ltd. [source] Highly fluorinated compounds induce phase separation in, and nanostructuration of liquid media.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2006Possible impact on, use in chemical reactivity control Abstract Liquid perfluorocarbons-like supercritical CO2 -provide valuable reaction media that can facilitate the separation of reaction products and the recovery of catalysts. Chemistry in fluorous media requires that some of the protagonist molecules, and in particular the catalysts, be grafted with one or more perfluoroalkylated chains. These chains, due to powerful hydrophobic and lipophobic effects, tend to self-assemble and induce the formation of a variety of nanocompartmented supramolecular architectures and colloids, such as micelles, vesicles, tubules, monolayers, and emulsions, thus generating microheterogenicity in the reaction medium. Fluorinated amphiphiles are, for example, known to generate fibrous gels in fluorous, organic, and aqueous media. Phase separation, nanocompartmentation, and interface-driven parameters can thus complicate otherwise simple chemistry. Conversely, they can provide useful micro- and nanoreactors and templates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4251,4258, 2006 [source] Stabilizer-free dispersion copolymerization of maleic anhydride and vinyl acetate.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2005Abstract A novel dispersion copolymerization of maleic anhydride (MAn) and vinyl acetate (VAc) without adding stabilizer is developed, which gives uniform copolymer microspheres with tunable sizes. Some principal factors affecting the microspheres, such as reaction time, monomer concentration and feed ratio, reaction media, and cosolvent, were investigated. It was found that the stabilizer-free dispersion copolymerization of MAn and VAc is a rapid process, and the particle size grows in accordance with the evolution of polymerization. The chemical composition of the copolymer microspheres was characterized by FT-IR and 13C NMR spectroscopies. Over a wide range of monomer concentrations, the microspheres can always be formed and stably dispersed, with uniform sizes ranging from 180 nm to 740 nm. The yield of copolymer microspheres reaches a maximum at 1:1 feed ratio of MAn to VAc, owing to the alternating copolymerization between the binary monomers by a known charge-transfer-complex mechanism. However, the diameter of microspheres drastically increases when MAn content is enhanced. Only some specific alkyl ester solvents, such as n -butyl acetate, isobutyl acetate, n -amyl acetate, are desirably fit for this unique stabilizer-free dispersion polymerization. Furthermore, we found that when some acetone is added as a cosolvent, the copolymer microspheres can still be formed, with much larger diameters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3760,3770, 2005 [source] A Novel, Facile Method for the Preparation of Uniform, Reactive Maleic Anhydride/Vinyl Acetate Copolymer Micro- and NanospheresMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2004Chang-Min Xing Abstract Summary: A novel, stabilizer-free dispersion polymerization with alkyl esters as reaction media gives uniform alternating microspheres of maleic anhydride (MAn)/vinyl acetate (VAc) copolymer. The diameter of the copolymer microspheres could be precisely controlled from 80 to 750 nm by changing the monomer concentration or feed ratio. Moreover, this new type of copolymer microspheres with reactive anhydride groups on the surface has good solubility in common nontoxic solvents such as water and ethanol. SEM image of the powder surface of copolymer microspheres formed at [MAn],=,[VAc],=,1.5 M. [source] Biphasic oligomerization of ethylene with nickel complexes immobilized in organochloroaluminate ionic liquidsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2009Lixia Pei Abstract Ethylene was selectively oligomerized by nickel complexes such as (PPh3)2NiBr2 and (PPh3)2NiCl2 immobilized in chloroaluminate ionic liquid in biphasic catalytic reactions. The influence of reaction parameters such as reaction media, reaction temperature and Et2AlCl:Ni molar ratio was also evaluated. Turnover frequency up to 24000 mol C2H4/(mol Ni h) was achieved under mild reaction conditions (0.5 atm and 40 °C). GC-MS analyses showed that the obtained oligomers completely consist of C4 and C6. The olefinic products can be easily separated from the catalytic ionic liquid phase by simple decantation, and the nickel catalyst can be reused without a significant decrease in turnover frequency and change of the distribution of the olefinic products. Copyright © 2009 John Wiley & Sons, Ltd. [source] Catalytic behaviors of enzymes attached to nanoparticles: the effect of particle mobilityBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2003Hongfei Jia Abstract Nanoparticles provide an ideal remedy to the usually contradictory issues encountered in the optimization of immobilized enzymes: minimum diffusional limitation, maximum surface area per unit mass, and high effective enzyme loading. In addition to the promising performance features, the unique solution behaviors of the nanoparticles also point to a transitional region between the heterogeneous (with immobilized enzymes) and homogeneous (with soluble free enzymes) catalysis. The particle mobility, which is related to particle size and solution viscosity through Stokes-Einstein equation, may impact the reaction kinetics according to the collision theory. The mobility-activity relationship was examined through experimental studies and theoretical modeling in the present work. Polystyrene particles with diameters ranging from 110,1000 nm were prepared. A model enzyme, ,-chymotrypsin, was covalently attached to the nanoparticles up to 6.6 wt%. The collision theory model was found feasible in correlating the catalytic activities of particles to particle size and solution viscosity. Changes in the size of particles and the viscosity of reaction media, which all affect the mobility of the enzyme catalyst, evidently altered the intrinsic activity of the particle-attached enzyme. Compared to KM, kcat appeared to be less sensitive to particle size and viscosity. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng84: 406,414, 2003. [source] PPh3 -Catalyzed Reactions of Alkyl Propiolates with N -Tosylimines: A Facile Synthesis of Alkyl 2-[aryl(tosylimino)methyl]acrylate and an Insight into the Reaction MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2010Huimin Liu Abstract A new PPh3 -catalyzed synthesis of alkyl 2-[aryl(tosylimino)methyl]acrylates from propiolate and N -tosylimine has been developed. Deuterium-labelling experiments show that the reaction mechanism involves several hydrogen-transfer processes, which are not the turnover-limiting step and strongly rely on the nature of the reaction media. The stable phosphonium,enamine zwitterion, which was proven to play an important role in the catalytic cycle, has been isolated and characterised by X-ray analysis. [source] An Efficient Hybrid, Nanostructured, Epoxidation Catalyst: Titanium Silsesquioxane,Polystyrene Copolymer Supported on SBA-15CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2007Lei Zhang Abstract A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single-site titanium active center, was immobilized successfully by in-situ copolymerization on a mesoporous SBA-15-supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380,m2,g,1) and pore volume (,0.46,cm3,g,1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert -butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two-phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites. [source] Diastereoselective Synthesis of Five- and Seven-Membered Rings by [2+2+1], [3+2], [3+2+2], and [4+3] Carbocyclization Reactions of ,-Substituted (Alkenyl)(methoxy)carbene Complexes with Methyl Ketone Lithium EnolatesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2005José Barluenga Prof. Dr. Abstract ,-Substituted alkenylcarbene complexes react with methyl ketone lithium enolates to give different carbocyclization products depending on the structure of the lithium enolate, on the metal of the carbene complex, and on the reaction media. Thus, the reactions of aryl and alkyl methyl ketone lithium enolates with ,-substituted alkenyl chromium and tungsten carbene complexes in diethyl ether afford 1,3-cyclopentanediol derivatives derived from a formal [2+2+1] carbocyclization reaction. However, the lithium enolates of acetone and tungsten complexes furnish formal [3+2+2] carbocyclization products. In the case of alkynyl methyl ketone lithium enolates, competitive formal [2+2+1] and [3+2] carbocyclization reactions occur and 1,3-cyclopentanediol and 3-cyclopentenol derivatives are formed. Conversely, alkenyl methyl ketone lithium enolates react with alkenylcarbene complexes under the same reaction conditions to form 2-cycloheptenone derivatives by a formal [4+3] carbocyclization reaction. Finally, when the reaction was performed in the presence of a coordinating medium, the [3+2] carbocyclization pattern was observed independently of the nature of the methyl ketone lithium enolate used. Los complejos alquenilcarbeno , -sustituidos reaccionan con enolatos de litio de metil cetonas para dar diferentes productos de carbociclación dependiendo de la estructura del enolato de litio, del metal del complejo carbeno y del medio de reacción. Así, la reacción de enolatos de litio de aril y alquil metil cetonas con complejos alquenilcarbeno de cromo y wolframio , -sustituidos en dietil eter origina derivados de 1,3-ciclopentanodiol, derivados de una reacción de carbociclación formal [2+2+1]. Sin embargo, el enolato de litio de la acetona y complejos de wolframio dan lugar a productos de carbociclación formal [3+2+2]. En el caso de enolatos de litio de alquinil metil cetonas, se observa la formación de una mezcla de derivados de 1,3-ciclopentanodiol y 3-ciclopentenol derivados de reacciones de carbociclación formal [2+2+1] y [3+2] competitivas. Por el contrario, los enolatos de litio de alquenil metil cetonas reaccionan con complejos alquenilcarbeno en las mismas condiciones de reacción para generar derivados de 2-cicloheptenona a través de una reacción de carbociclación formal [4+3] Finalmente, cuando la reacción se lleva a cabo en presencia de PMDTA, un medio coordinante, se observa el modelo de carbociclación formal [3+2], independientemente de la naturaleza del enolato de litio utilizado. [source] Methyltrioxorhenium Catalysis in Nonconventional Solvents: A Great Catalyst in a Safe Reaction MediumCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2010Marcello Crucianelli Dr. Abstract The requirement that chemical processes are sustainabable, reflected in waste reduction and the use of safe reagents and reaction conditions, is becoming even more stringent as a result of pressure by society and governments to preserve the environment and protect human health. Catalysis offers numerous benefits related to green chemistry, including lowered energetic reaction requirements; catalytic, rather than stoichiometric, amounts of materials; increased selectivity; lowered consumption of processing and separation agents; and, in many cases, the use of less-toxic compounds. Our research group has for a long time been studying methyltrioxorhenium in the oxyfunctionalization of different substrates, by using H2O2 or its urea-hydrogen peroxide complex as the primary oxidant. In this Review paper we aim to provide a full literature account on the catalytic activity and selectivity of methyltrioxorhenium in the oxyfunctionalization reaction, either in nonconventional solvents or under solvent-free conditions, with a particular emphasis on the use of ionic liquids as green reaction media. [source] Electrochemical reduction of benzoylformic acid in ionic liquidCHINESE JOURNAL OF CHEMISTRY, Issue 9 2003Jia-Xing Lu Abstract Ionic liquids possess a number of unique properties that make them ideal electrolytes. Electrochemical reduction of benzoylformic acid in room temperature ionic liquids as reaction media could be conducted with excellent performances without any additional supporting electrolyte. Electrolysis at glassy carbon electrode results in the formation of mandelic acid in 91% yield. And the electrochemical behavior of benzoylformic acid was investigated with the technique of cyclic voltammetry. [source] The asymmetric synthesis of (R,R)-formoterol via transfer hydrogenation with polyethylene glycol bound Rh catalyst in PEG2000 and waterCHIRALITY, Issue 2 2010Ling Huang Abstract (R,R)-formoterol was synthesized in seven steps with 4-hydroxyl-3-nitro-acetophenone as the starting material. The key intermediate, the chiral secondary alcohol 4, was prepared via Rh-catalyzed asymmetric transfer hydrogenation with (S,S)-PEGBsDPEN as the ligand and sodium formate as the hydrogen donor under mild conditions. With a mixture of PEG 2000 and water as the reaction media, the catalyst system could be recycled four times. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] Chiral synthesis of secondary alcohols using Geotrichum candidumCHIRALITY, Issue 9 2002Kaoru Nakamura Abstract Chiral synthesis of secondary alcohols of both the (S)- and (R)-enantiomer with extremely high enantioselectivities (up to >99% ee) using a biocatalyst, Geotrichum candidum, is reviewed. Resting cell and dried-cell preparation using acetone were applied to oxidation, reduction, and deracemization reactions. Many methods to improve the reactivity and enantioselectivity of the reactions were developed. For example, additives such as secondary alcohols and hydrophobic resin (AmberliteÔ XAD) were used in nonaqueous reaction media such as organic and supercritical solvents as well as in aqueous ones. As a result, optically pure alcohols of both enantiomers were synthesized on a gram scale. Chirality 14:703,708, 2002. © 2002 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||||||||