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901.
M. Lundbäck 《Polymer Degradation and Stability》2006,91(5):1071-1078
Plaques of branched polyethylene stabilized with 0.1 wt.% 4,4′-thiobis(6-tert-butyl-3-methylphenol) [Santonox® R] were aged at different temperatures between 75 and 95 °C in anaerobic (nitrogen or water) and aerobic (air or water saturated with air) media. Antioxidant concentration profiles were obtained by oxidation induction time (OIT) measurements using differential scanning calorimetry. Results obtained by high performance liquid chromatography of extracts confirmed that the gradual decrease in OIT with increasing ageing time was due to migration of antioxidant to the surrounding medium. The antioxidant concentration profiles along the plaque thickness direction were flat in the plaques aged in the non-aqueous media indicating that the migration of antioxidant to the surrounding medium was controlled by the low evaporation rate at the material boundary. Crystals of antioxidant were detected by optical microscopy on the samples exposed to nitrogen. The similarity of the antioxidant concentration profiles obtained after ageing in nitrogen and in air suggested that the fraction of the antioxidant oxidized is negligible in comparison with the loss of antioxidant by migration to the surrounding media. The antioxidant concentration profiles along the plaque thickness direction obtained after ageing in water were less flat, suggesting faster dissolution in the water phase than evaporation in the case of non-aqueous ageing. The antioxidant diffusivity could be determined from the aqueous experiments and was in reasonable agreement with data reported by Moisan. For the samples exposed to water, the loss of antioxidant was faster from the samples exposed to water saturated with air. This difference is attributed to a faster degradation of the antioxidant in the oxygen-containing water phase increasing the mass transport from the polymer phase boundary to the water phase. 相似文献
902.
《Tetrahedron: Asymmetry》2006,17(19):2761-2767
Two novel chiral spiro nitrogen-containing ligands, 7,7′-bis(2-pyridinecarboxamido)-1,1′-spirobiindane (abbreviated as SIPAD) and 7,7′-bis(2-quinolinecarboxamido)-1,1′-spirobiindane (abbreviated as SIQAD), were conveniently prepared from 1,1′-spirobiindane-7,7′-dicarboxylic acid in high yields (85% and 84%, respectively) in two steps. The cobalt complexes prepared in situ from Co(OAc)2 and the ligands have been proven to be efficient catalysts for the asymmetric Michael addition reaction of malonates to chalcone derivatives. The alkylation products were obtained in high yields with moderate enantiomeric excesses under mild reaction conditions. 相似文献
903.
《Journal of photochemistry and photobiology. A, Chemistry》2006,177(2-3):248-252
Steady-state and time resolved luminescence quenching measurements of (2T/2E)Cr(phen)33+ were used to investigate the association of phenols to sodium dodecyl sulfate (SDS) micelles. Steady-state results show the quenching process occurs in the micellar pseudo phase. Scatchard plots indicate that the process is a partition between aqueous and micelles. The k+ and k− rate constant have been evaluated from time resolved data and the binding constants were obtained. The trend found in the K's were 4-H-Ph < 2,6-diMe-Ph < 4-Br-Ph. We concluded that it is possible to use *Cr(phen)33+ as a luminescent probe to determine association parameters for quenchers to micelles of SDS. 相似文献
904.
Mono-η-arenebis(trimethylphosphine(rhenium chemistry: alkyl,hydrido, halogeno and olefin derivatives
《Polyhedron》1986,5(8):1363-1370
Co-condensation of rhenium atoms with a benzene-trimethylphosphine mixture gives the dimer [Re(ν-C6H6)(PMe3)2]2 which is a precursor to the new compounds Re(η-C6H6)(PMe3)2R (R = H, Cl, I, Me, Et, CHCH2 or Ph), [Re(η-C6H6)(PMe3)2X2]BF4 (X2 = H2 or HI), [Re(η-C6H6)(PMe3)2H2][BF4]2, and [Re(η-C6H6)(PMe3)2L]BF4 (L = η-C2H4 or CO). Co-condensation of manganese atoms with benzene-trimethylphosphine gives Mn(η-C6H6)(PMe3)2H. 相似文献
905.
《Polyhedron》1986,5(7):1297-1301
The irradiation of Fe(III) protoporphyrin IX [Fe(III)PPIX) in a thoroughly deoxygenated 35% ethanol-water solution containing pyrazine (pyz) leads to changes in the visible spectrum that are indicative of Fe(II)PP species formation. With a large excess of pyz the spectrum is similar to that of the Fe(II) pyridine hemochrome, suggesting that the monomer Fe(II)PP(pyz)2 is formed. With a lower pyz content, the photochemically formed bis-pyz complex converts to a polymeric Fe(II)PP species. A similar photochemical behaviour is observed when piperazine or 4,4′-bipyridine are used as bridge ligands instead of pyz. The origin of the absorptions characteristic of the photoreaction products is discussed on the basis of the dependence of the spectra on the nature of the bridge ligands. 相似文献
906.
《Polyhedron》1986,5(9):1429-1436
A comparative study of the catalyzed decomposition of hydrogen peroxide using the following copper(II) complex salts, Cu(bipy)(S-threo)Cl · 3H2O, Cu(phen)(S-threo)Cl · 2H2O, Cu(bipy)(S-prol)Cl · 2H2O and Cu(phen)(S-prol)Cl · 2H2O has been made. Kinetic parameters were experimentally determined by the polarographic method at 25°C, pH 7.7 and constant ionic strength (μ = 0.1 M NaNO3). The catalytic behavior of the chelate with 2,2′-bipyridine and S-prolinate was also studied at pH 6.5 and 8.5. The reactivity follows the sequence: [Cu(bipy)S-prol] > [Cu(phen)S-prol] > [Cu(bipy)S-threo] > [Cu(phen)S-threo]. Activation energies are very similar to each other. The pH-dependent exchange of the amino acid ligand with hydrogen peroxide seems to be a critical factor in the reaction pathway. Several reaction mechanisms are proposed. 相似文献
907.
《Polyhedron》1986,5(3):707-710
Copper and nickel powders react directly with sodium dithiocarbamates in organic solvents and produce the corresponding metal complexes. The rate constants have been estimated spectrohotometrically. The effects of organic solvents and substituents of the carbamates on the relative reactivity were studied. The results show that copper powder reacts in chloroform more readily than any other system examined. This reaction has been successfully applied to the determination of copper contents in brass and bronze powders. 相似文献
908.
《Polyhedron》1986,5(10):1625-1628
The hydrogenation of imines using RhCl(PPh3)3 and [Rh(PPh3)2(diene)]PF6 as catalyst precursors is effective at room temperature under 1 atm of hydrogen, using alcohols as solvents. A water-diethylether phase-transfer system has been used for a solid imine. A catalytic cycle featuring hydrogen bonding between a coordinated alcohol and an imine, and involving a dialkylamido intermediate, is proposed. 相似文献
909.
《Polyhedron》1986,5(11):1733-1740
Reaction of protonated 2,2′-bipyridine (bpy) with octacyanometalates(IV and V), [M(CN)8]n− (M = Mo or W, n = 3 or 4), gave the following complexes: {(bpyH)3[M(CN)8]·4H2O}, {(bpyH)3(H3O)[M(CN)8]·H2O}, {(bpyH2)2[W(CN)8]·3H2O} and {(bpyH2)K2[W(CN)8]·2H2SO4·7H2O}. These salts were characterized by electron absorption and reflectance spectrometry, IR, Raman and ESR spectrometry, thermo gravimetry and differential thermal analysis, cyclic voltammetry and potentiometry. The solubility of the salts in water and some polar organic solvents has been measured. The intensively coloured salts of molybdenum(IV) and tungsten(IV) have been discussed in terms of the bpyH+-[M(CN)8]4− ion pairs, which exhibit an outer-sphere electron transfer between adjacent redox sites. 相似文献
910.
《Polyhedron》1986,5(11):1821-1827
The dark purple title compound was prepared by reaction of Ru2Cl(O2CCH3)4 with molten 6-fluoro-2-hydroxypyrine (Hfhp) in quantitative yield. Crystals of composition Ru2Cl(fhp)4 were obtained by slow diffusion of hexane into a CH2Cl2 solution of the compound. The crystals belong to the tetragonal space group I4mm with the following unit-cell dimensions: a = b = 10.890(2) Å, c = 13.178(4) Å, α = β = γ = 90.0°, V = 1562.8(6) Å3, and Z = 2. The Ru2Cl(fhp)4 molecule, which has crystallographic 4mm (C4c) symmetry, contains a diruthenium(II,III) unit with a metalmetal bond order of 2.5. The four bridging fhp ligands across the Ru2 unit are oriented in one direction to form a polar molecule. The coordinatioin spheres of the two ruthenium atoms [Ru(1) and Ru(2)] are Ru(2)N(I)4 and Ru(1)Cl(1)O(1)4, respectively. The axial site on Ru(1) is blocked by four F(1) atoms. The Ru(1)Ru(2), Ru(2)Cl(1), Ru(2)O(1) and Ru(1)N(1) distances are 2.284(1), 2.427(3), 1.971(2) and 2.089(4) Å, respectively. The electronic spectrum of the compound in CH2Cl2 shows two strong bands at 552 nm (ε = 4720 M−1 cm−1) and 355 nm ε = 3770 M−1 cm−1). Cyclic voltammetry of Ru2Cl(fhp)4 in CH2Cl2 in the presence of 0.1 M [N(C2H5)4]ClO4 at 100 mV s−1 shows two quasireversible metal-centered one-electron oxication and reduction processes at +1.68 (ΔEp = 120 mV) and −0.01 V (ΔEp = 126 mV), respectively, vs an AgAgCl reference electrode. 相似文献