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排序方式: 共有785条查询结果,搜索用时 156 毫秒
41.
Dr. Dmitry Katayev Kai F. Pfister Timo Wendling Prof. Dr. Lukas J. Gooßen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9902-9905
Various (hetero)arenecarboxylic acids were converted to the corresponding Daugulis amides and nitrated selectively in the ortho‐position in the presence of [CuNO3(PPh3)2] and AgNO2 at 50 °C. A microwave‐assisted saponification allows regenerating the carboxylate group within minutes, which may then be removed tracelessly by protodecarboxylation, or substituted by aryl‐ or alkoxy‐groups via decarboxylative cross‐coupling. 相似文献
42.
为创建洁净高效的酚类化合物硝化工艺,以杂多酸H6PMo9V3O40(PMAV3)为活性组分,硅胶为载体,浸渍法制备了负载型催化剂PMAV3/SiO2,采用红外光谱、X射线衍射谱、N2吸附-脱附法及TG-DSC分析等测试技术对该催化剂的结构及热稳定性进行了表征;考察了该催化剂对多种酚类化合物硝化反应的催化性能。结果显示,该催化剂对多种酚类化合物的硝化反应具有很强的催化活性和区域选择性,产率为83.7%~94.5%,其中苯酚、邻甲酚、邻氯苯酚和邻氟苯酚以邻位硝化产物居多,水杨酸的对位硝化产物占绝对优势;负载催化剂的织构性质与载体相近,但随负载量增加,比表面积逐渐降低;PMAV3/SiO2的热稳定性好于本体PMAV3。催化剂回收容易,重复使用5次,活性基本不变。 相似文献
43.
44.
Chan?Yoon?Jung Hoe?Jin?Hah Seung?Hoon?Han Hong-Woo?Park Sang?Man?KooEmail author 《Journal of Sol-Gel Science and Technology》2005,33(1):81-85
Tin oxide-doped hybrid particles were prepared by a wet chemical process with organic-inorganic (phenyl/silica) hybrid particles in an alcoholic solution. The phenyl/silica hybrid particles, with a diameter of ca. 790 nm were used as a new support material for tin oxide (SnO2) particles from tin(IV) chloride. The surface of the particles was modified via nitration of aromatic groups in the particles, to promote formation of the tin oxide coating on the particles. The thickness and surface morphology of the tin oxide layer coated on the nitrated-phenyl/silica hybrid particles could be controlled by varying the tin(IV) chloride concentration and reaction time. The size and morphology of the resultant particles were investigated with field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The particles obtained were also characterised by infrared (FTIR) and solid-state 13C magic angle spinning nuclear magnetic resonance (13C-CP/MAS NMR) spectroscopy. The effect of processing parameters on the crystallinity and structure of the doped hybrids were confirmed by X-ray diffraction (XRD) patterns. 相似文献
45.
密闭系统中微波辅助萃取机制探讨 总被引:9,自引:2,他引:9
通过与普通加热萃取虎杖中白藜芦醇的产率进行对比 ,对密闭系统中微波辅助萃取的机理进行了探讨。结果表明 ,微波辅助萃取与普通加热萃取二者的活化能相差不大 ,分别为30.06和30.32kJ·mol-1。但微波辅助萃取的表观速率常数约是普通加热萃取的20倍。并且还利用电子扫描显微镜对样品微结构进行了观察 ,研究表明 ,细胞内极性成分如水吸收了微波能后压力迅速增加导致细胞结构的破坏是MAE快速高效的关键 ,由于细胞的破坏 ,萃取剂和萃取目标化合物更容易通过细胞壁 ,加速了扩散速度 ,进而加速了萃取速度。 相似文献
46.
47.
Microwave-assisted thermal desorption (MAD) coupled to headspace solid-phase microextraction (HS-SPME) has been studied for
in-situ, one-step, sample preparation for PAHs collected on XAD-2 adsorbent, before gas chromatography with mass spectrometric
detection. The PAHs on XAD-2 were desorbed into the extraction solution, evaporated into the headspace by use of microwave
irradiation, and absorbed directly on a solid-phase microextraction fiber in the headspace. After desorption from the SPME
fiber in the hot GC injection port, PAHs were analyzed by GC–MS. Conditions affecting extraction efficiency, for example extraction
solution, addition of salt, stirring speed, SPME fiber coating, sampling temperature, microwave power and irradiation time,
and desorption conditions were investigated. Experimental results indicated that extraction of 275 mg XAD-2, containing 10–200 ng
PAHs, with 10-mL ethylene glycol–1 mol L−1 NaCl solution, 7:3, by irradiation with 120 W for 40 min (the same as the extraction time), and collection with a PDMS–DVB
fiber at 35 °C, resulted in the best extraction efficiency. Recovery was more than 80% and RSD was less than 14%. Optimum
desorption was achieved by heating at 290 °C for 5 min. Detection limits varied from 0.02 to 1.0 ng for different PAHs. A
real sample was obtained by using XAD-2 to collect smoke from indoor burning of joss sticks. The amounts of PAHs measured
varied from 0.795 to 2.53 ng. The method is a simple and rapid procedure for determination of PAHs on XAD-2 absorbent, and
is free from toxic organic solvents. 相似文献
48.
49.
微波辅助提取-气相色谱法同时测定中草药中有机磷和氨基甲酸酯农药残留 总被引:1,自引:0,他引:1
建立了中草药中有机磷和氨基甲酸酯类农药同时检测的气相色谱分析新方法.中药材试样依据正交实验的优化条件,用正己烷-丙酮(1∶4,V∶V)混合提取剂进行微波辅助提取,经弗罗里硅土和中性氧化铝混合层析柱净化后,采用HP-5毛细管柱分离,氮磷检测器同时检测中草药中15种有机磷和6种氨基甲酸酯类农药残留量.21种农药在0.01~1.0 mg/L的浓度范围内线性良好,线性相关系数为0.9950~1.000,检出限为0.002~0.01 mg/L.在0.05、0.2、0.5 mg/kg三个添加水平的平均回收率分别为75.11%~128.57%、75.85%~120.71%和76.43%~117.25%,相对标准偏差分别为 3.10%~10.58%、5.27%~9.94%和4.03%~9.03%.方法用于中草药中有机磷和氨基甲酸酯类农药残留的同时检测,结果良好. 相似文献
50.