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991.
Whereas tropinone derived nonaflate 3 was no suitable precursor for Heck-reactions, the related carbamate 7 was an excellent substrate for palladium-catalyzed processes. Nonaflate 7 was either isolated in excellent yield by LDA treatment of ketone 5 followed by trapping with NfF (nonafluorobutanesulfonyl fluoride) or generated in situ by fluoride-catalyzed reaction of silyl enol ether 6 with NfF. The desired 1,3-diene 8 was prepared by conventional Heck-reaction of nonaflate 7 with methyl acrylate in almost quantitative yield. Alternatively, the one-pot nonaflation-Heck protocol starting from silyl enol ether 6 provided 8 in good yield. The couplings of acrylonitrile or phenyl vinyl sulfone were also performed with in situ generated 7 and they afforded the expected 1,3-dienes 9 and 10 in good yields. The Sonogashira-reaction with phenylacetylene also started from silyl enol ether 6 and provided enyne 11 via 7 in good yield. A Diels-Alder reaction of 1,3-diene 8 with N-phenyl maleimide at 100 °C furnished tetracyclic adduct 12 in good yield, with excellent diastereofacial selectivity, but with low endo-exo-selectivity. Nonaflate 14 was easily obtained from the corresponding unsaturated bicyclic ketone 13. It behaved differently in an attempted Heck-reaction and mainly led to fragmentation products 15 and 16, whereas the expected 1,3-diene 17 was formed only as minor component. However, 14 could successfully be used in a Sonogashira-reaction with phenylacetylene to afford compound 18. These transformations demonstrate the great potential of tropinone derived alkenyl nonaflates for diversity oriented syntheses of interesting compounds containing an 8-azabicyclo[3.2.1]octane scaffold. 相似文献
992.
Zong ChunYan Gao QingYu Wang YuMei Feng JiaMin Mao ShanCheng Zhang Lu 《中国科学B辑(英文版)》2007,50(2):205-211
The ferroin-catalyzed Belousov-Zhabotinsky(BZ) reaction,the oxidation of malonic acid by acidic bromate,is the most commonly investigated chemical system for understanding spatial pattern forma-tion. Various oscillatory behaviors were found from such as mixed-mode and simple period-doubling oscillations and chaos on both Pt electrode and Br-ISE at high flow rates to mixed-mode oscillations on Br-ISE only at low flow rates. The complex dynamic behaviors were qualitatively reproduced with a two-cycle coupling model proposed initially by Gy?rgyi and Field. This investigation offered a proper medium for studying pattern formation under complex temporal dynamics. In addition,it also shows that complex oscillations and chaos in the BZ reaction can be extended to other bromate-driven nonlinear reaction systems with different metal catalysts. 相似文献
993.
Virginie Gueu Hongpeng You Tomokatsu Hayakawa Masayuki Nogami 《Journal of Sol-Gel Science and Technology》2007,41(3):231-236
Fluorescence and spectral hole burning properties of Eu3+ ions were studied in nanocrystals-precipitated SnO2-SiO2 glasses. The glasses were prepared to contain various amount of Eu2O3 using the sol-gel method, in which SnO2 nanocrystals were precipitated by heating in air. In the glasses containing Eu2O3 less than 1%, the Eu3+ ions were preferentially doped in the SnO2 nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons
and holes excited in SnO2 crystals. The SnO2 nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence
intensities of the Eu3+ ions. With the increasing Eu2O3 concentration, the amount of SnO2 nanocrystals decreased and the Sn4+ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities
and the hole depth to decrease. 相似文献
994.
Mesoporous amorphous MnO<Subscript>2</Subscript> as electrode material for supercapacitor 总被引:1,自引:0,他引:1
Mao-Wen Xu Dan-Dan Zhao Shu-Juan Bao Hu-Lin Li 《Journal of Solid State Electrochemistry》2007,11(8):1101-1107
A kind of novel mesoporous, electrochemical active material, amorphous MnO2 has been synthesized by an improved reduction reaction and using supramolecular as template. The synthesized sample was characterized
physically by thermogravimetric analysis, X-ray diffraction, transmission electron microscope (TEM), and Brunauer–Emmett–Teller
(BET) surface area measurement, respectively. Electrochemical characterization was performed using cyclic voltammetry and
chronopotentiometry in 2 mol/l KOH aqueous solution electrolyte. The results of BET and TEM analysis indicated that supramolecular
template plays an important role in the process of big specific surface area mesoporous material forming. After sintering
at 200 °C, the sample still remained an amorphous structure, and its specific capacitance reached 298.7 F/g and presented
a very stable capacitance after 500 cycles. In addition, the electrochemical process, such as ion transfer and electrical
condition, was also investigated with electrochemical impedance spectroscopy. 相似文献
995.
996.
Endre Nagy 《Central European Journal of Chemistry》2003,1(2):160-177
A heterogeneous, multi-layer mass transfer model is proposed for prediction of the effect of multi-layer packing of catalyst
particles adhered to the gas-liquid interface. The behavior of the mass transfer rate with respect to the multi-layer packing,
to the particle size and mass transfer coefficient without particles is discussed. It is shown that enhancement can be considerably
increased by multi-layer packing compared to that of mono-layer packing, depending on the values of particle size and mass
transfer coefficient. The predicted mass transfer rates using the proposed model was verified with experimental data taken
from the literature. The model presented should be superior to that of published in the literature. 相似文献
997.
New Copper Complexes Containing Phosphaalkene Ligands. Molecular Structure of [Cu{P(Mes*)C(NMe2)2}2]BF4 (Mes* = 2,4,6‐tBu3C6H2) Reaction of equimolar amounts of the inversely polarized phosphaalkene tBuP=C(NMe2)2 ( 1a ) and copper(I) bromide or copper(I) iodide, respectively, affords complexes [Cu3X3{μ‐P(tBu)C(NMe2)2}3] ( 2 ) (X =Br) and ( 3 ) (X = I) as the formal result of the cyclotrimerization of a 1:1‐adduct. Treatment of 1a with [Cu(L)Cl] (L = PiPr3; SbiPr3) leads to the formation of compounds [CuCl(L){P(tBu)C(NMe2)2}] ( 4a ) (L = PiPr3) and ( 4b ) (L = SbiPr3), respectively. Reaction of [(MeCN)4Cu]BF4 with two equivalents of PhP=C(NMe2)2 ( 1b ) yields complex [Cu{P(Ph)C(NMe2)2}2]BF4 ( 5b ). Similarly, compounds [Cu{P(Aryl)C(NMe2)2}2]BF4 ( 5c (Aryl = Mes and 5d (Aryl = Mes*)) are obtained from ArylP=C(NMe2)2 ( 1c : Aryl = Mes; 1d : Mes*) and [(MeCN)4Cu]BF4 in the presence of SbiPr3. Complexes 2 , 3 , 4a , 4b , and 5b‐5d are characterized by means of elemental analyses and spectroscopy (1H‐, 13C{1H}‐, 31P{1H}‐NMR). The molecular structure of 5d is determined by X‐ray diffraction analysis. 相似文献
998.
Ab initio molecular orbital theory and density functional theory have been used to study nine isomers of N7 ionic clusters with low spin at the HF/6-31G*, MP2/6-31G*, B3LYP/6-31G*, and B3LYP/6-311(+)G* levels of theory. All stationary
points are examined with harmonic vibrational frequency analyses. Four N7
+ isomers and five N7
− isomers are determined to be local minima or very close to the minima on their potential-energy hypersurfaces, respectively.
For N7
+ and N7
−, the energetically low lying isomers are open-chain structures (C
2
v
and C
2
v
or C2). The results are very similar to those of other known odd-number nitrogen ions, such as N5
+, N9
+, and N9
−, for which the open-chain structures are also the global minima. This research suggests that the N7 ionic clusters are likely to be stable and to be potential high-energy-density materials if they could be synthesized.
Received: 16 July 2001 / Accepted: 8 October 2001 / Published online: 21 January 2002 相似文献
999.
The ionic liquid 1-N-butyl-3-methylimidazolium chloride ([C4mim]+Cl−) was investigated as reaction media for the homogeneous acylation of cellulose with 2-furoyl chloride in the presence of
pyridine. The preparation of cellulose furoate depending on the reaction conditions, the cellulose type and the pyridine content
was studied. Cellulose furoates with a degree of substitution in the range from 0.46 to 3.0 were accessible, i.e., under mild
conditions, with a low excess of reagent and in a short reaction time. The products were characterized by elemental analysis,
perpropionylation, 1H- and 13C NMR spectroscopy and FTIR spectroscopy.
Thomas Heinze is the member of the European Polysaccharide Network of Excellence (EPNOE), www.epnoe.eu 相似文献
1000.
In this study, poly(N-methylolacrylamide)/polymethylacrylamide (PNMA/PMAA) hybrids were produced successfully by frontal free-radical polymerization
at ambient pressure. In a typical run, the appropriate amounts of reactants (N-methylolacrylamide, NMA; methylacrylamide, MAA) and initiator (ammonium persulfate) were dissolved in dimethyl sulfoxide
at ambient temperature. Frontal polymerization (FP) was initiated by heating the wall of the tube with a soldering iron, and
the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. Once initiated, no further energy
was required for polymerization to occur. The dependences of the front velocity and front temperature on the initiator concentration,
reactant dilution, and NMA/MAA components were thoroughly investigated. The front temperatures were between 69 and 116 °C,
depending on the persulfate concentration. We have also investigated the FP of PNMA/PMAA hybrids with N-methyl-2-pyrrolidone as solvent. Results show that FP can be exploited as a means for the preparation of PNMA/PMAA hybrids
with the potential advantage of higher throughput compared to the traditional mode. 相似文献