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排序方式: 共有418条查询结果,搜索用时 718 毫秒
41.
Patricia Amouzegh Annie Finiels Patrick Geneste Erick Ginestar Patrice Moreau 《Catalysis Letters》1995,34(3-4):389-394
The acylation reaction of 2-butylbenzofuran withp-anisoyl chloride andp-anisic acid in the presence of faujasite type zeolites, in the liquid phase, is reported. A good initial selectivity to the 3-acylated derivative is obtained, but the selectivity decreases with time. This result is explained by the involvement of a deacylation-reacylation process. 相似文献
42.
We recently described an improved method to synthesize poly(ether-ketones) or PEKs. It utilized an optimized mixture of polyphosphoric acid (PPA) and P2O5 that is not only milder, less corrosive and less expensive than super-acid media, but also can play the multiple roles of solvent, Friedel-Crafts catalyst and dehydrating agent. The as-prepared PEKs from such a highly viscous reaction medium displayed unexpected, thermally induced relaxation exotherms regardless of the amorphous or semi-crystalline nature of polymer. This thermal behavior was not observed for the formally identical polymers [viz. pPEK or poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene] which is normally semi-crystalline) that were separately prepared in a much less viscous mixture of methanesulfonic acid and P2O5 (Eaton's reagent) or N-methyl-2-pyrrolidinone (NMP). Such an observation was first made when both samples of pPEKs were subjected to the same thermal history and the thermal relaxation exotherms were observed only for the pPEK sample that was prepared in PPA/P2O5 medium. Further confirmation of viscosity-and-shear-induced strain stored in the as-synthesized PEKs was provided by a systematic annealing study with differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) analysis and Fourier-transform infrared spectroscopy (FT-IR). Based on these data, pPEK was successfully compression-molded in the temperature range of 230-250 °C which is more than 100 °C below its melting temperature. 相似文献
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对-氟苯酚与硫酸二甲酯进行酚甲醚化得到对-氟苯甲醚,然后在AlCl3催化下与顺丁烯二酸酐进行Friedel-Crafts酰基化,进一步去甲基化得到4-(4-氟-2-苯酚)-4-氧代-2-丁烯酸,在碱性条件下,经自身环化得到6-氟-4-氧代-3,4-二氢-2H-1-苯并吡喃-2-甲酸,关环步骤的收率为81%;最后在乙酸介质中,用5%Pd/C催化加氢得到外消旋的6-氟-3,4-二氢-2H-1-苯并吡喃-2-羧酸。该工艺总收率为51.87%,具有合成路线短、收率高、原料易得、条件温和、操作简单的特点,适宜工业化生产。 相似文献
46.
磷钨酸铯催化合成对甲氧基苯乙酮 总被引:3,自引:2,他引:1
以磷钨酸铯(Cs2.5H0.5PW12O40)为催化剂合成了对甲氧基苯乙酮(p-MOAP),采用傅里叶变换红外光谱、X射线衍射、N2吸附和NH3程序升温脱附等方法对Cs2.5H0.5PW12O40催化剂进行了表征;考察了Cs2.5H0.5PW12O40催化剂活化温度、反应条件及反应产物等对苯甲醚乙酰化反应的影响。表征结果显示,多孔性的Cs2.5H0.5PW12O40催化剂保持了H3PW12O40的Keggin结构和酸强度,但酸量明显小于H3PW12O40。实验结果表明,适宜的p-MOAP合成条件为:300℃下活化的Cs2.5H0.5PW12O40催化剂用量为0.18g(以20mmol乙酸酐计)、n(苯甲醚):n(乙酸酐)=10、反应温度115℃、反应时间40min。在此条件下进行了4次重复实验,p-MOAP的收率达61.3%~64.8%、选择性达96.10%~96.80%。苯甲醚乙酰化反应的产物p-MOAP和醋酸对Cs2.5H0.5PW12O40催化剂的活性具有抑制作用。 相似文献
47.
采用两步浸渍法制备了硅胶负载磷钨酸铯催化剂Cs2.5H0.5PW12O40/SiO2,将其用于催化合成对甲氧基苯乙酮(p-MOAP)。采用X射线衍射、傅里叶变换红外光谱和NH3程序升温脱附等技术对Cs2.5H0.5PW12O40/SiO2催化剂进行了表征,考察了Cs2.5H0.5PW12O40负载量、催化剂用量、反应物配比、反应温度、反应时间等对p-MOAP合成反应的影响。表征结果显示,Cs2.5H0.5PW12O40和Cs2.5H0.5PW12O40/SiO2催化剂保持了H3PW12O40的Keggin结构,且Cs2.5H0.5PW12O40/SiO2催化剂中Cs2.5H0.5PW12O40主要聚集在载体表面。实验结果表明,优化的合成p-MOAP工艺条件为:Cs2.5H0.5PW12O40负载量为30%(质量分数)的Cs2.5H0.5PW12O40/SiO2催化剂用量为4%(占总物料的质量分数)、苯甲醚与乙酸酐的摩尔比为10、反应温度100℃、反应时间120min。在此条件下,使用新鲜催化剂时,p-MOAP的收率达到83.4%,选择性达到96.1%。 相似文献
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Tomoshige Fujino Taishi Kondo Prof. Dr. Hiroaki Suga Prof. Dr. Hiroshi Murakami 《Chembiochem : a European journal of chemical biology》2019,20(15):1959-1965
Flexizymes are tRNA acylation ribozymes that have been successfully used to facilitate genetic code reprogramming. They are capable of charging acid substrates onto various tRNAs and tRNA analogues. However, their minimal RNA substrate has not been investigated. Here we have designed fluorescently labeled short RNAs corresponding to the four, three, and two bases (4bRNA, 3bRNA, 2bRNA) at the tRNA 3′-end and explored the minimal RNA substrate of flexizymes, dFx and eFx. 3bRNA was the observed minimal RNA substrate of the flexizymes, but the efficiency of acylation of this short RNA was two to three times lower than that of 4bRNA. The efficiency of acylation of 4bRNA was comparable with that of the microhelix, a 22-base RNA conventionally used as a tRNA analogue for analyzing acylation efficiency. We also compared the efficiencies of acylation of the microhelix and 4bRNA with various acid substrates. Thanks to the short length of 4bRNA, its acyl-4bRNA products exhibited larger mobility shifts in gel electrophoresis than those exhibited by acyl-microhelix products with every substrate tested. This indicated that 4bRNA was an ideal RNA substrate for analyzing the efficiency of acylation by flexizymes. 相似文献
50.
邻硝基对甲苯胺合成方法的改进 总被引:2,自引:0,他引:2
将对甲苯胺用冰醋酸酰化,得对甲基乙酰苯胺,然后以二氯乙烷为溶剂经硝酸硝化后直接滴加到稀 NaOH 溶液中中和、水解制得邻硝基对甲苯胺。此工艺与国内目前采用的传统合成工艺相比,生产周期短,反应总收率从79.9%提高到88.3%。 相似文献