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Different Organic Solvents (different + organic_solvent)
Selected AbstractsKinetics and mechanism of the oxidative regeneration of carbonyl compounds from oximes by pyridinium bromochromateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2006Pradeep K. Sharma The oxidative deoximination of several aldo- and keto-oximes by pyridinium bromochromate (PBC), in dimethylsulfoxide, exhibited a first-order dependence on both the reductant (oxime) and the oxidant (PBC). The oxidation of ketoximes is slower than that of aldoximes. The rates of oxidation of aldoximes correlated well in terms of the Pavelich,Taft dual substituent-parameter equation. The low positive value of polar reaction constant indicated a nucleophilic attack by a chromate-oxygen on the carbon. The reaction is subject to steric hindrance by the alkyl groups. The reaction of acetaldoxime has been studied in 19 different organic solvents. The solvent effect has been analyzed by Taft's and Swain's multiparametric equations. A mechanism involving the formation of a cyclic intermediate, in the rate-determining step, has been proposed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 364,368, 2006 [source] Kinetics and mechanism of the oxidation of some ,-hydroxy acids by 2,2,-bipyridinium chlorochromateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2002Vinita Kumbhat The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by 2,2,-bipyridinium chlorochromate (BPCC) in dimethylsulphoxide leads to the formation of corresponding oxoacids. The reaction is first order each in BPCC and the hydroxy acids. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the form: kobs = a + b [H+]. The oxidation of ,-deuteriomandelic acid exhibited a substantial primary kinetic isotope effect (kH/kd = 5.29 at 303 K). Oxidation of p -methylmandelic acid was studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 248,254, 2002 [source] Solubility and phase separation of poly(L,D -lactide) copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Marja Rissanen Abstract In this study, the solubility and precipitation properties of medical-grade stereocopolymers were investigated. The solubility of the polymers was tested with eight different organic solvents and four nonsolvents. The solubility of poly(L,D -lactide) stereocopolymers was highly dependent on the L/D ratio of the copolymer. The phase-separation ability was tested by cloud-point titration with a solvent and a nonsolvent. The solvent was in all cases dichloromethane, and the nonsolvents were n -hexane, methanol, ethanol, and isopropyl alcohol. The results showed that n -hexane was the most efficient nonsolvent. Methanol and ethanol showed quite similar precipitation properties. Isopropyl alcohol was the least efficient nonsolvent of those studied. Also, the L/D ratio of the copolymer had an effect on the precipitation properties. The precipitation happened most easily when the L content was high. The molecular weight of the copolymer had only a slight effect on the phase separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis, characterization, and comparison of properties of novel fluorinated poly(imide siloxane) copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Anindita Ghosh Abstract Four new poly(imide siloxane) copolymers were prepared by a one-pot solution imidization method at a reaction temperature of 180°C in ortho -dichlorobenzene as a solvent. The polymers were made through the reaction of o -diphthaleic anhydride with four different diamines,4,4,-bis(p -aminophenoxy-3,3,-trifluoromethyl) terphenyl, 4,4,-bis(3,-trifluoromethyl- p -aminobiphenyl ether)biphenyl, 2,6-bis(3,-trifluoromethyl- p -aminobiphenyl ether)pyridine, and 2,5-bis(3,-trifluoromethyl- p -aminobiphenylether)thiopene,and aminopropyl-terminated poly dimethylsiloxane as a comonomer. The polymers were named 1a, 1b, 1c, and 1d, respectively. The synthesized polymers showed good solubility in different organic solvents. The resulting polymers were well characterized with gel permeation chromatography, IR, and NMR techniques. 1H-NMR indicated that the siloxane loading was about 36%, although 40 wt % was attempted. 29Si-NMR confirmed that the low siloxane incorporation was due to a disproportionation reaction of the siloxane chain that resulted in a lowering of the siloxane block length. The films of these polymers showed low water absorption of 0.02% and a low dielectric constant of 2.38 at 1 MHz. These polyimides showed good thermal stability with decomposition temperatures (5% weight loss) up to 460°C in nitrogen. Transparent, thin films of these poly(imide siloxane)s exhibited tensile strengths up to 30 MPa and elongations at break up to 103%, which depended on the structure of the repeating unit. The rheological properties showed ease of processability for these polymers with no change in the melt viscosity with the temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Polystyrene nanocomposite materials by in situ polymerization into montmorillonite,vinyl monomer interlayersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Ahmed Akelah Abstract A different series of new polystyrene,clay nanocomposites have been prepared by grafting polymerization of styrene with vinyl-montmorillonite (MMT) clay. The synthesis was achieved through two steps. The first step is the modification of clay with the vinyl monomers, such as N,N -dimethyl- n -octadecyl-4-vinylbenzyl-ammonium chloride, n -octadecyl-4-vinylbenzyl-ammonium chloride, triphenyl-4-vinylbenzyl-phosphonium chloride, and tri- n -butyl-4-vinylbenzyl-phosphonium chloride. The second step is the polymerization of styrene with different ratios of vinyl-MMT clay. The materials produced were characterized by different physical and chemical methods: (1) IR spectra, confirming the intercalation of the vinyl-cation within the clay interlayers; (2) thermogravimetric analysis (TGA), showing higher thermal stability for PS,nanocomposites than polystyrene (PS) and higher thermal stability of nanocomposites with of phosphonium moieties than nanocomposites with ammonium moieties; (3) swelling measurements in different organic solvents, showing that the swelling degree in hydrophobic solvents increases as the clay ratio decreases; (4) X-ray diffraction (XRD), illustrating that the nanocomposites were exfoliated at up to a 25 wt % of organoclay content; and (5) scanning electron microscopy (SEM), showing a complete dispersion of PS into clay galleries. Also, transmission electron microscopy (TEM) showed nanosize spherical particles of , 150,400 nm appearing in the images. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3739,3750, 2007 [source] The influence of organic solvent and ionic liquids on the selective formation of 2-(2-ethylhexyl)-3-phenyl-1,2-oxaziridine mediated by lipases,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Thiago Bergler Bitencourt Abstract This paper describes the influence of the addition of ionic liquids (ILs) based on [BMIm][X], where [X],=,SCN, Cl, BF4, and PF6, on the chemo-enzymatic oxidation of N -benzyliden-2-ethylhexylamine to form the corresponding E- and Z -isomers of oxaziridines mediated by Pseudomonas sp. (PSL) and Candida antarctica (CAL-B) lipases in various organic solvents at room temperature (25,°C) with urea hydrogen peroxide (UHP). The results showed that the use of different organic solvents in the presence of ILs, critically changes the conversions (5,99%) and the isomeric ratio E:Z, (50,100% E -isomer) of the products formed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Spectroscopic studies of charge transfer complexes of meso -tetra- p -tolylporphyrin and its zinc complex with some aromatic nitro acceptors in different organic solventsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2007Mohamed E. El-Zaria Abstract The charge transfer complex (CTC) formation of 5,10,15,20-tetra(p -tolyl)porphyrin (TTP) and zinc 5,10,15,20-tetra(p -tolyl)porphyrin with some aromatic nitro acceptors such as 2,4,6-trinitrophenol (picric acid), 3,5-dinitrosalicylic acid, 3,5-dinitrobenzoic acid (DNB) and 2,4-dinitrophenol (DNP) was studied spectrophotometrically in different organic solvents at different temperatures. The spectrophotometric titration, Job's and straight line methods indicated the formation of 1:1 CTCs. The values of the equilibrium constant (KCT) and molar extinction coefficient (,CT) were calculated for each complex. The ionization potential of the donors and the dissociation energy of the charge transfer excited state for the CTC in different solvents was also determined and was found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the electron affinity of the acceptors and the nature of the solvent. No CT band was observed between Zn-TTP as donor and DNP or DNB as acceptors in various organic solvents at different temperature. Bimolecular reactions between singlet excited TTP (1TTP*) and the acceptors were investigated in solvents with various polarities. A new emission band was observed. The fluorescence intensity of the donor band decreased with increasing the concentration of the acceptor accompanied by an increase in the intensity of the new emission. The new emission of the CTCs can be interpreted as a CT excited complex (exciplex). Copyright © 2007 John Wiley & Sons, Ltd. [source] Beneficial properties of lactic acid bacteria isolated from a Rana catesbeiana hatcheryAQUACULTURE RESEARCH, Issue 14 2009Sergio E Pasteris Abstract This work addresses the selection of potentially probiotic lactic acid bacteria (LAB) to be used in raniculture. Thus, strains belonging to the genera Pediococcus pentosaceus, Leuconostoc mesenteroides, Lactococcus lactis and Enterococcus faecium isolated from a Rana catesbeiana hatchery were evaluated for their inhibitory properties against RLS-associated pathogens (Proteus vulgaris, Pseudomonas aeruginosa, Staphylococcus epidermidis) and food-borne bacteria. Cell-free supernatants of LAB strains inhibited the growth of at least one of the pathogens by organic acids, but L. lactis CRL 1584 also produced a bacteriocin-like metabolite. The ability of LAB strains to produce H2O2 in MRS+TMB medium was also studied. Seventy-eight to ninety six per cent of the strains showed some level of H2O2 production. Moreover, different organic solvents were used to determine the hydrophobicity and Lewis acid/base characteristic of LAB strain surfaces. Most of the strains presented hydrophilic properties, but no acidic or basic surface characters. However, some strains isolated from the skin showed a high degree of hydrophobicity and basic components in the cell surface due to their adhesion to chloroform. These properties were not observed in LAB from balanced feed and freshwater. Taking into account general guidelines and the beneficial properties studied, five strains were selected as potential candidates to be included in a probiotic for raniculture. [source] Effect of solvent concentration on the extraction kinetics and diffusivity of Cyclosporin A in the fungus Tolypocladium inflatumBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2007May Ly Abstract The kinetics of solid-liquid extraction and extraction yields of the immunosuppressant drug Cyclosporin A (CyA) from the mycelia of Tolypocladium inflatum were examined in this study. A 2 L stirred, baffled vessel was used to extract CyA from wet mycelia mass. Three different organic solvents were used, namely, methanol, acetone, and isopropanol at different concentrations in aqueous mixtures at room temperature. It was found that the best solvent was acetone at 50% v/v concentration achieving 100% extraction of CyA from the mycelia of T. inflatum. Although acetone proved to be the better solvent for CyA extraction, further studies were performed using methanol. A linear relationship was found between extraction yield of CyA and methanol concentration with 100% CyA extraction at 90% v/v methanol. The partition coefficients of CyA between the solid mycelia phase and the aqueous solvent phase were found to decrease exponentially with increasing methanol concentration. A liquid extraction model was developed based on the diffusion equation to correlate the kinetic data of CyA extraction from the solid mycelia of T. inflatum. Non-linear regression analysis of experimental data was used with the diffusion equation in order to calculate the effective diffusivities of CyA in the mycelia of T. inflatum. For all three organic solvents used, the effective diffusivities of CyA were found to be between 4.41,×,10,15 and 6.18,×,10,14 m2/s. This is the first time CyA effective diffusivities in T. inflatum are reported in the literature. Biotechnol. Bioeng. 2007;96: 67,79. © 2006 Wiley Periodicals, Inc. [source] A New Class of Low-Molecular-Weight Amphiphilic GelatorsCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2005Nils Mohmeyer Abstract A new powerful class of low-molecular-weight amphiphilic compounds has been synthesized and their structure,property relationships with respect to their gelation ability of organic solvents have been investigated. These compounds are able to gel organic solvents over a broad range of polarity. Especially polar solvents such as valeronitrile and ,-butyrolactone can be gelled even at concentrations far below 1 wt,%. It was found that the gelation ability of these asymmetrically substituted p -phenylendiamines depends on a well-balanced relation of the terminal head group, the units involved in hydrogen bonding (amide or urea groups), and on the length of the alkyl chain. With this class of new gelators it is possible to tailor thermal and mechanical properties in different organic solvents and open various application possibilities. [source] | ||||||||||