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Solvent Media (solvent + media)
Selected AbstractsCorrelation analysis of reactivity in the oxidation of anilines by nicotinium dichromate in nonaqueous mediaINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2006D. S. Bhuvaneshwari The kinetics of oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate (NDC) in different organic solvent media in the presence of p -toluenesulfonic acid (TsOH) has been investigated. The rate of the reaction is zero order with respect to substrate, first order in NDC, and is found to increase with increase in [TsOH]. The various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species-anilines reaction (k2) correlates with Hammett's substituent constants affording negative reaction constants. The effect of para- and meta-substituents on the oxidation rates confirms to Swain et al.'s substituent constants F and R, both with negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and E while showing satisfactory correlation with Kamlet,Taft's solvatochromic parameters (,, ,, and ,*). © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 657,665, 2006 [source] Effect of solvent and structure on the kinetics and mechanism of the aquation of bromopentaamine cobalt(III) complex in binary aqueous mixturesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2004Gehan M. El-Subruiti The kinetics of aquation of bromopentaamine cobalt(III) complex have been investigated spectrophotometrically in aqueous-organic solvent media using acetonitrile, urea, and dimethyl sulfoxide as co-solvents at 45 , T (°C) , 65. The logarithms of rate constant of the aquation reaction vary nonlinearly with the reciprocal of the dielectric constant for all cosolvent mixtures, indicating a specific solute,solvent interaction. Also, the rate constants are correlated with the total number of moles of water and the organic solvents. However, the solvent effects on the solvation components of the enthalpy of activation, ,H,, and the entropy of activation, ,S,, have been studied. Analysis of the solvent effect confirmed a common Id mechanism for the aquation of the cobalt(III) complex. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:494,499, 2004 [source] Enantioselective Reduction of 4-Fluoroacetophenone at High Substrate Concentration using a Tailor-Made Recombinant Whole-Cell CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Harald Gröger Abstract A practical and highly efficient biocatalytic synthesis of optically active (R)-4-fluorophenylethan-1-ol has been developed based on reduction of the corresponding 4-fluoroacetophenone in the presence of a tailor-made recombinant whole-cell biocatalyst, containing an alcohol dehydrogenase and a glucose dehydrogenase. The reaction proceeds in a pure aqueous solvent media at a substrate concentration of ca. 0.5,M, and gives the desired product with high conversion (>95,%), good yield (87,%) and with an excellent enantioselectivity of >99,% ee. In addition, activity tests further showed that also the analogous 2- and 3-fluoroacetophenones are promising substrates. [source] Preparation and Characterisation of Pd Nanoclusters in Hyperbranched Aramid Templates to be used in Homogeneous CatalysisMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 12 2003Daniela Tabuani Abstract In the present paper the potential use of hyperbranched (HB) aramids as metallic solution stabilisers and carriers for homogeneous catalysis is outlined. Aramids, synthesised either from A2,+,B3 reagents [namely, p -phenylenediamine (PPD) and trimesic acid (TMA)] or from an AB2 monomer [i.e., 5-(4-aminobenzamido)isophtalic acid, named ABZAIA], have been used to stabilise palladium nanoclusters dispersed in two solvent media, namely N,N, -dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The influence of the nature of the polymeric support as well as of the solvent medium on both cluster dimensions and stability of the solutions has been investigated. Indeed, the interactions between the polymeric support and the metallic precursor (PdCl2), as revealed by 1H NMR spectroscopy, involve only the amino groups of the HB aramids. Metal nanocluster dimensions and stability are strongly dependent on the polymer used as a stabilizer. Transmission electron microscopy (TEM) analysis has shown that the presence of HB polymer in the solution reduces cluster dimensions and allows the obtaining of stable systems. The low concentration of NH2 end groups in the poly(AB2) system leads to the formation of Pd particles of rather low dimensions with a high tendency to aggregate. All prepared solutions are stable under inert atmosphere for at least a month, with an improved stabilisation when using the poly(A2,+,B3) system for more than five months. A TEM micrograph of poly(ABZAIA)/Pd from a DMSO solution. [source] A New Method to Test the Effectiveness of Sunscreen Ingredients in a Novel Nano-surface Skin Cell MimicPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2006Rajagopal Krishnan Photophysical properties of sunscreens are commonly studied in solvent media, which do not mimic the skin, or in complex artificial skin systems, which are difficult to handle. In an earlier study, we showed that polystyrene nanosphere suspensions mimic the mixed polarity environment of skin cell systems. This paper presents a new method to quantify the effectiveness of sunscreens in the polystyrene nanosphere environment. This method utilizes the intrinsic UV-B fluorescence of polystyrene nanospheres. We studied three UV-B sunscreens by this new method and compared their extinction coefficients with observed values in solvent. The values follow the trend observed in solvents, but the ratio of their extinction coefficient in solvent to the value obtained by this new method is 1.3,1.8 instead of 1. This difference might be caused by the mixed polarity or the microgeometry of the nanosphere system. Regardless of the difference in the extinction coefficients, this new system can be used to test hundreds of chemicals for their sunscreening potential in a cost-effective way. One marked advantage of this new method is its ability to test both hydrophobic and hydrophilic sunscreening chemicals in the same environment. This is virtually impossible for current solvent-based models, which require different solvents for hydrophobic and hydrophilic chemicals. The new method also allows the simultaneous evaluation of a host of photophysical properties of sunscreening chemicals. [source] Influence of solvent on the structures of two one-dimensional cobalt(II) coordination polymers with tetrachloroterephthalateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Yong-Qin Fang The title cobalt coordination polymers, catena -poly[[[aquatripyridinecobalt(II)]-,-tetrachloroterephthalato] pyridine solvate], {[Co(C8Cl4O4)(C5H5N)3(H2O)]·C5H5N}n, (I), and catena -poly[[[diaquadipyridinecobalt(II)]-,-tetrachloroterephthalato] 1,4-dioxane trihydrate], {[Co(C8Cl4O4)(C5H5N)2(H2O)2]·C4H8O2·3H2O}n, (II), have been prepared with tetrachloroterephthalic acid (H2BDC-Cl4) under different solvent media. Both complexes form infinite cobalt(II),tetrachloroterephthalate polymeric chains. In (I), two independent CoII ions are six-coordinated through N3O3 donor sets in slightly distorted octahedral geometries provided by two carboxylate and three pyridine ligands, and one water molecule. The structure of (II) contains two independent CoII atoms, each lying on a twofold axis, which adopt a tetragonally distorted N2O4 octahedral geometry via two carboxylate groups, two pyridine ligands and two water molecules. The different stoichiometry of coordinated and solvent guest molecules leads to different two-dimensional supramolecular networks, with (I) utilizing C,H..., and weak ,,, interactions and (II) utilizing mainly conventional hydrogen bonding. [source] The effects of conformation and solvation on optical rotation: Substituted epoxides,CHIRALITY, Issue 3-4 2008Shaun M. Wilson Abstract The vapor-phase optical rotation (or circular birefringence) of (S)-1,2-epoxybutane, (S)-epichlorohydrin, and (S)-epifluorohydrin has been measured at the nonresonant excitation wavelengths of 355 nm and 633 nm by means of Cavity Ring-Down Polarimetry (CRDP). Complementary solution-phase studies were performed in a wide variety of dilute solvent media to highlight the pronounced influence of solute,solvent interactions. Density functional theory calculations of optical activity have been enlisted to unravel the structural and electronic provenance of experimental observations. Three stable, low-lying conformers have been identified and characterized for each of the targeted chiral species, with thermal (relative population weighted) averaging of their antagonistic chiroptical properties allowing specific rotation values to be predicted under both isolated and solvated conditions. For (S)-epichlorohydrin and (S)-epifluorohydrin, a self-consistent isodensity polarizable continuum model (SCI-PCM) has been exploited to gain further insight into the underlying nature of solvation effects. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] | ||||||||||