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981.
The thermal reaction of HNCO has been studied in a static cell at temperatures between 873 and 1220 K and a constant pressure of 800 torr under highly diluted conditions. The reaction was measurable above 1000 K by FTIR spectrometry. The products detected include CO, CO2, HCN, NH3, and the unreacted HNCO. In this moderate temperature regime, the rates of product formation and HNCO decay cannot be accounted for by a previously established high-temperature mechanism, assuming HNCO → NH + CO (1) as the initiation process. Instead, a new bimolecular reaction, 2HNCO → CO2 + HNCNH (2), has been invoked to interpret the disappearance of HNCO as well as the formation of various products, most importantly CO2. The concentration profiles of all measured species can be quantitatively modeled, throughout the temperature range analyzed, by varying k2 using a modified mechanism. The kinetically modeled values of k2 can be effectively represented by This result agrees closely with that computed with the conventional transition-state theory using the TST parameters predicted by the BAC-MP4 method: The bimolecular reaction takes place via a stable 4-membered ring intermediate which is isoelectronic with diketene; viz. 相似文献
982.
The first discrete, selenium-centered tetranuclear zinc cluster [Zn4(mu4-Se)[Se2P(OPr)2]6] was isolated and characterized. The cluster consists of six edge-bridged dsep ligands with four zinc atoms in a slightly distorted tetrahedron and a mu4-Se atom in the center. In addition, 12 mu2-bridging selenium atoms form a Se12 icosahedron. From variable-temperature 31P NMR studies, it was observed that the cluster [Zn4(Se)[Se2P(OPr)2]6] is partly decomposed to [Zn[Se2P(OPr)2]2] and the monomeric species [Zn[Se2P(OPr)2]2] is further in equilibrium with its dimer [Zn[Se2P(OPr)2]2]2. 相似文献
983.
984.
Cui X Yu SH Li L Biao L Li H Mo M Liu XM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(1):218-223
Selective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag(2)MoO(4) and Ag(6)Mo(10)O(33) can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo(17)O(47), Ag(2)Mo(2)O(7,) Ag(6)Mo(10)O(33) were observed under different pH conditions. Ag(6)Mo(10)O(33) nanowires with uniform diameter 50-60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 degrees C. The melting point of Ag(6)Mo(10)O(33) nanowires were found to be about 238 degrees C. Similarly, Ag(2)WO(4), and Ag(2)W(2)O(7) nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale. 相似文献
985.
锂辉石—石灰石烧结中煤粉代替重油作燃料的研究和实践 总被引:1,自引:0,他引:1
目前世界锂工业原料以锂辉石为主。我国锂辉石储量居世界首位,主要分布于新疆、四川、湖南等地,其中又以四川的储量占全国第一。锂的主要基础化合物LiOHH2O系用锂辉石-石灰石烧结法而得,烧结燃料是影响LiOHH2O产品价格的重要因素之一。过去国内外均采用... 相似文献
986.
987.
We report a ruthenium-catalyzed reaction for various 3-benzyl but-1-ynyl ethers with suitable functionalities. Treatment of these substrates with TpRu(PPh3)(CH3CN)2PF6 (8.0 mol %) catalyst in 1,2-dichloroethane (80 degrees C, 12 h) afforded functionalized 1,3-dienes and benzyl aldehyde in good yields. This process is considered to be a tandem dealkoxylation and transfer hydrogenation. Deuterium-labeling experiments reveal that the migration of different hydrogen atoms proceeds regiospecifically. A plausible mechanism is proposed on the basis of the results of isotope experiment. 相似文献
988.
Densities have been measured for the electrolyte (NaCl, NaBr and NaI)‐monosaccharide (D ‐mannose and D‐ribose)‐water solutions at 298.15 K. These data have been used to calculate the apparent molar volumes of the saccharides (VΦ,S) and electrolytes (VΦ,E) in the studied solutions. Infinite dilution apparent molar volumes, VΦ,S0 and VΦ,E0, have been evaluated, together with the standard transfer volumes of the saccharides (ΔtVS0) from water to aqueous electrolyte solutions and those of the electrolytes (ΔtVE0) from water to aqueous saccharide solutions. It was shown that both the ΔtVS0 and ΔtVE0 values are positive and increase with increasing molalities of sodium halides and saccharides, respectively. Overall, the ΔtVS0 and ΔtVE0 values have the order of NaCl > NaBr > NaI except for NaI‐ribose and NaI‐ribose. Volumetric interaction parameters for the electrolyte‐monosaccharide pairs in water were obtained and interpreted by the stereochemistry of the monosaccharide molecules and the structural interaction model. 相似文献
989.
Liu JA Petzold CJ Ramirez-Arizmendi LE Perez J Kenttämaa H 《Journal of the American Chemical Society》2005,127(37):12758-12759
Laser-induced acoustic desorption combined with mass spectrometry has been used to demonstrate that phenyl radicals can attack dinucleoside phosphates at both the sugar and base moieties, that purine bases are more susceptible to the attack than pyrimidine bases, and that the more electrophilic the radical, the more efficient the damage to dinucleoside phosphates. 相似文献
990.
A high-performance liquid chromatographic method for the simultaneous separation and determination of nine podophyllum lignans and two flavonoids in Podophyllum emodi Wall.var.chinesis Sprague was established. The separation was performed with the following condition: column, Kromasil-C18, 5 μm, 15 × 0.46 cm; solvent A, 25 mM phosphate buffer, pH 2.5; solvent B, methanol; gradient, 50/50/70% B at 0/13/33 min; flow rate, 0.8 mL min?1; detection, UV 270 nm. β-Apopicropodophyllin was used as the internal standard. The samples of P. emodi Wall.var.chinesis Sprague from different sources were examined by the developed method. In addition, three methods for sample preparation were discussed. It is shown from the results that refluxing in chloroform displays high extraction efficiency. 相似文献