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Reaction Solvent (reaction + solvent)
Selected AbstractsConformationally Biased Selective Alkylation of trans -Cyclohexane-1,2-bis(sulfonamide) Assisted by Solvent-Tuned Protecting Groups: Applications to the Synthesis of a Large Optically Active Polyazamacrocycle,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006Carmen Peña Abstract The selective alkylation of (R,R)-cyclohexane-1,2-bis(sulfonamide) with trityl bromoalkyl ethers has been studied in detail. The major formation of either mono- or dialkylated compounds clearly depends on the right combination of protecting groups and the reaction solvent. An exhaustive study suggests that this effect can be reasonably explained by the conformational preferences of the monoalkylated compounds, which also depend on the reaction medium, solvophobic effects and weak intramolecular interactions. Structural analysis by NOE measurements showed the presence of folded conformations in solution for all the tested examples. Monte Carlo conformational searches supported this proposal, showing a very good correlation between the fraction of folded species and the selectivity towards monoalkylation. Finally, tuning of the reaction conditions, leading to either extended or folded conformations of the monoalkylated synthetic intermediates, was exploited for the efficient synthesis of a large optically active polyazamacrocycle. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Multipurpose box- and azabox-Based Immobilized Chiral CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006Abstract Azabis(oxazolines) can be used as chiral ligands in the copper-catalyzed enantioselective Mukaiyama aldol reaction. When supported on solids, azabis(oxazoline)-copper complexes are more easily deactivated than their analogous bis(oxazoline)-copper complexes, and are not compatible with the use of coordinating solvents in the method of preparation. The performance of the immobilized catalysts (up to 86,% ee) depends on the support and the reaction solvent, with some positive effect on enantioselectivity due to surface effects. The deactivation is not irreversible and the deactivated catalysts show excellent performance in the cyclopropanation reaction, providing added value to the supported multipurpose catalysts. [source] Synthesis of a model cyclic triblock terpolymer of styrene, isoprene, and methyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2002Dimitris Pantazis Abstract The synthesis of a model cyclic triblock terpolymer [cyclic(S- b -I- b -MMA] of styrene (S), isoprene (I), and methyl methacrylate (MMA) was achieved by the end-to-end intramolecular amidation reaction of the corresponding linear ,,,-amino acid precursor [S- b -I- b -MMA] under high-dilution conditions. The linear precursor was synthesized by the sequential anionic polymerization of S, I, and MMA with 2,2,5,5-tetramethyl-1-(3-lithiopropyl)-1-aza-2,5-disilacyclopentane as an initiator and amine generator and 4-bromo-1,1,1-trimethoxybutane as a terminator and carboxylic acid generator. The separation of the unreacted linear polymer from the cyclic terpolymer was facilitated by the transformation of the unreacted species into high molecular weight polymers by the evaporation of the reaction solvent and the continuation of the reaction under high-concentration conditions. The intermediate materials and the final cyclic terpolymer, characterized by size exclusion chromatography, vapor pressure osmometry, thin-layer chromatography, IR and NMR spectroscopy, exhibited high molecular weight and compositional homogeneity. Dilute-solution viscosity measurements were used as an additional proof of the cyclic structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1476,1483, 2002 [source] Preparation of Pie-Shaped and Rugged Aromatic Polyamide ParticlesMACROMOLECULAR REACTION ENGINEERING, Issue 5 2008Yayoi Yoshioka Abstract Aromatic polyamide particles were prepared by reacting diamines and diacid chlorides in a reaction solution containing water. They consisted of submicron-sized pie-shaped or rugged spherical particles with a narrow size distribution. The surface morphology of these particles was found to vary with the volume of water added, the reaction solvent, and the monomer concentration, but the degree of crystallinity of the particles obtained was almost the same. In addition, the molecular weight of the resulting material depended on the volume of water added and the monomer concentration. During the particle formation process, the degree of crystallinity was set at the initial stage, and thereafter the morphology and the molecular weight changed gradually with reaction time. [source] Enhanced Glucose to Fructose Conversion in Acetone with Xylose Isomerase Stabilized by Crystallization and Cross-LinkingBIOTECHNOLOGY PROGRESS, Issue 5 2004Kati M. Vilonen The effects of acetone and ethanol on glucose to fructose conversion catalyzed by soluble and cross-linked crystalline (CLXIC) xylose isomerase were studied. Relative to pure buffer solvent, the fructose production rate was more than doubled in 50% acetone. The same kind of increase in the isomerization rate was not seen with ethanol. Increase both in acetone and in ethanol concentration in the reaction solvent enhanced the production of fructose. At 50 °C in pure buffer solvent the reaction mixture contained 49% fructose in equilibrium and in 90% acetone the fructose equilibrium content was 64%. Furthermore, CLXIC was relatively stable in the presence of high concentration of acetone: 70,80% of activity was left after incubation for 24 h at 50 °C in buffer solutions (pH 7.2) containing 10,90% acetone. In buffer containing 50% ethanol only 2% of the initial activity of CLXIC was retained after 24 h at 50 °C. Soluble xylose isomerase was considerably less stable than CLXIC in both acetone- and ethanol-containing solutions. These results show that the addition of acetone enhances the production of fructose from glucose by enhancing the reaction rate and shifting the equilibrium toward fructose. However, xylose isomerase must be in the form of cross-linked crystals for maximal activity and stability. [source] Subcritical Water Reaction Behavior of D -Glucose as a Model Compound for Biomass Using Two Different Continuous-Flow Reactor ConfigurationsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2009T. Saito Abstract Recently, cellulosic materials have been considered as a useful resource for the recovery of valuable chemicals and liquid fuels, etc. Cellulose is a homopolymer of D -glucose, which is often used as a model compound for biomass. Reactions of D -glucose in subcritical water as the reaction solvent were conducted using a single-flow-type reactor (S1) and an admixture-type reactor with feed and preheated-water flow (S2) at temperatures from 200 to 240,°C, pressures from 15 to 20 MPa, residence times from 40 to 120 s, and initial feed concentrations of 1.5,10 wt %. D -Glucose was converted into aldehydes, organic acids and furans, with mainly organic acids obtained at 240,°C. D -Glucose decomposition using reactors S1 and S2 revealed that the conversion rate of D -glucose was promoted more using S2 than by S1. The yield of furans with S1 was higher than with S2, while the yield of organic acids from S1 was lower than that from S2. [source] Surface modification of inorganic oxide particles with silane coupling agent and organic dyesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2001Jun Lin Abstract The silane coupling agent 3-glycidoxypropyl trimethoxylsilane (GPS) was grafted onto the surface of silica gel, P2 glass beads and TiO2 oxide particles. FT-IR, thermogravimetric and elemental analysis were used to characterize the modified particles. The effects of various factors on the GPS grafting efficiency such as catalyst, GPS concentration, reaction temperature and time were studied. After modification with GPS, the xanthene dye rhodamine B and azo dyes 4-phenylazophenol and 4-phenylazoaniline, respectively, were grafted on to the particles, which were then used as pigment fillers. The colors of the pigments were adjusted by changing the kind of dyes, the concentration, the pH and the reaction solvents. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||