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<正>光敏氧化反应是上世纪中叶发展起来的重要有机反应,它以洁净、节能和高效为特点,与传统的热化学氧化方法比较,避免了重金属氧化剂的使用和排放,是一项绿色氧化技术,在对环保日益关注的今天受到化学家们的广泛重视.甾体化合物构成临床药物中的一个大类.从甾体皂甙元降解产物出发可以制备出众多甾体类药物.甾体皂甙元的传统氧化方法是利用化学计量的铬酐作氧化剂,其使用给环境带来极大的污染,因此研究洁净的氧化新方法既具有理论意义,又具有应用前景.本文分别以薯蓣皂甙元和番麻皂甙元为原料,成功地利用光敏氧化反应实现了假甾体皂甙元的环内烯醇双键的氧化断裂,为甾体皂甙元的洁净氧化开辟了新途径.具体研究结果如下: 相似文献
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利用三种方法合成偏诺皂甙类化合物 总被引:1,自引:0,他引:1
利用三种重要的糖苷化方法, 合成了6个偏诺皂甙类化合物(7~12). 在三种合成方法中, 分别选择了单糖及二糖的卤苷供体、三氯亚胺酯供体及硫苷供体(1~6)以考察它们与受体偏诺皂甙元的反应结果. 利用偏诺皂甙元在3位和17位羟基上的位阻差异, 使偏诺皂甙元17位羟基在不被保护的情况下与每种糖供体只在其3位羟基发生选择性反应. 相似文献
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薯蓣皂甙元具有增强心脏收缩力,减慢心率,抗动脉硬化,改善微循环,抗衰老以及抗关节炎等功效.但由于薯蓣皂甙元水溶性非常差,其临床应用受到了很大的限制.迄今为止,只有薯蓣皂甙元水溶性衍生物--皂甙的生产方法及其临床应用(如地奥心血康)报道.为进一步了解薯蓣皂甙元的其它水溶性衍生物的生理活性,我们以薯蓣皂甙元为原料,设计并合成了一系列的薯蓣皂甙元衍生物及其盐(图1和图2)[1-5].这些化合物的水溶性比薯蓣皂甙元明显增加,而且它们对大鼠都具有抗心肌梗死活性. 相似文献
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首次利用薯蓣皂甙元的完整骨架经16步反应以7.6%的总收率合成了骨化三醇(1α,25-二羟基维生素D3)的光化反应前体. 3-苄基保护的薯蓣皂甙元经还原开E/F环产生3,16,26-胆甾三醇-3-苄醚(5). 除去化合物5 C-16羟基后, 其C-26羟基经消除和羟基化反应转移到C-25位. 目标分子A/B环结构单元通过薯蓣皂甙元A/B环的官能团转化被构筑. 按照已知的光化反应, (1S,3R)-胆甾-5,7-二烯-1,3,25-三醇能被转化成为1α,25-二羟基维生素D3. 相似文献
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Akitomo Tachibana 《Journal of mathematical chemistry》1991,7(1):95-110
A geometrical model for estimating the effects of external fields upon a reaction path is proposed. The reaction path is defined as the intrinsic reaction coordinate (IRC) which is treated as a string. The IRC frame is introduced in order to uniquely determine the attitude of the string with respect to the reaction medium. The string is thrown in the external fields of the reaction medium, and slides or rotates, and is deformed. The cell structure attached to the string is also deformed. A perturbational approach to the reaction rate formula is presented. 相似文献
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Photochromic reaction of water insoluble 1,3,3-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2-indoline] (SP) was studied in water with the aid of vesicles and -cyclodextrin (-CD). In both systems, the photochromic reaction of SP was observable in spite of the low solubility of SP in water. In order to examine the microenvironment around the SP and the reaction product, photomerocyanin (MC), in those systems, the spectrum of MC was measured in various organic solvent of various polarity. Decreasing the polarity of the solvent decreased the peak absorbance and shifted the peak wavelength to the long wavelengths. When the vesicles were used, the reactant, SP, and the product, MC, were solubilized in different regions of different polarity. The reaction substrate was then supposed to have moved from the hydrophobic region of the membrane to the hydrophilic one after the photoisomerzation. The photochromic reaction of SP in the presence of -CD was slower than in the vesicles and faster than that in methanol. The polarity in the vesicular membrane and the limited rotation of the reactant in the cavity of -CD may have influenced the reaction rate. The prolonged light irradiation period resulted in a simultaneous photoreaction and polymerization, producing some unknown side reaction. 相似文献
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The reaction of B2H4 with acetylene has been studied by the MNDO method. It is shown that the reaction is exothermic and proceeds in two steps. The first step is the formation of a three-center -complex and this is the rate-determining step of the reaction. The second step is the rearrangement of the -complex to the product and this step requires a very small amount of activation energy. The activation barrier for the diboration reaction is 12.8 kcal/mol.The proposed mechanism is significantly different from those proposed earlier and explains all experimental data relating to this reaction. 相似文献
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The kinetic significance of elementary steps in the liquid-phase reaction of ethylbenzene oxidation inhibited by ionol (2,6-di-tert-butyl-4-methylphenol) was determined with the use of the value method. The nature of the effectiveness of ionol from the class of ortho-substituted phenols was considered. It consists in a ponderable role of the reaction of chain carriers (peroxy radicals) with the inhibitor with a decrease in the contribution of the reverse reaction. In this case, the relatively weak participation of the antioxidant at the step of degenerate chain branching and the high reaction rate constant of the interaction of phenoxy radicals with each other are of considerable importance. The value ranking of steps allowed us to diminish them; this simplified the reaction mechanism under various initial conditions. A satisfactory agreement between base reaction mechanisms, which describe experimental results and the behavior of the inhibited reaction under new reaction conditions, is considered as a reliability criterion for the prediction made. 相似文献
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The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature (T) on the cure kinetics was explored in detail. It was observed that the data of gel time (t gel, i.e. the time when the reaction reaches the gel point) or a specific reaction time (t nc) (defined as the reaction time before which time the influence of confinement of network on the diffusion of reaction components can be neglected) versus T obey certain functional relationship, which was well explained by the cure kinetics model of thermoset network. The cure kinetics for the two-component silicone rubber can be well fitted by the Kamal-Sourour(autocatalyst) reaction model rather than Kissinger model. When the reaction time was before or equal to t nc, the reaction order obtained by the Kamal-Sourour reaction model was 2, which was consistent with the reaction order inferred from the two components chemical reaction when the diffusion of reaction components was not influenced by the formed cross-linked polymer network. When the reaction time was larger than t nc, such as to the end of reaction (t e), the influence of confinement of network on the diffusion of reaction components cannot be neglected, and the reaction order obtained by the Kamal-Sourour reaction model was larger than 2. It was concluded that the confinement effect of network had a greater influence on the cure kinetics of the silicone rubber. The reaction rate constants (k r) under different temperatures were also determined by Kamal-Sourour reaction model. The activation energy (E) for the two-component silicone rubber was also calculated from the results of lnt gel, lnt nc, and lnk r versus 1/T, respectively. The three values of E were close, which indicated that above analyses were self-consistent. 相似文献
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Using currently available thermochemical and kinetic data and estimation methods to analyze the thermochemistry and the kinetic parameters of the elementary reactions involved in the oxidation of HCl and HBr, reaction mechanisms are proposed which account for the previously reported reaction products, the rate law, and the kinetic data. For oxidation of HCl, two competitive pathways, the radical initiation by hydrogen abstraction and the fourcenter reaction pathway, were invoked to account for the observations. In the oxidation of HBr one must invoke a fast surface reaction of the type to account for the reaction. 相似文献
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醇和胺的借氢反应是一种制备胺类化合物的绿色途径。本文介绍了借氢反应的概念,并重点介绍了均相催化的醇和胺之间借氢反应的起源、重要进展以及未来的发展趋势。 相似文献
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The reaction of ethyl chloronitroacetate with carbonyl compounds of the aliphatic series under the conditions of the Reformatsky reaction in ether, THF, or benzene does not proceed with the substitution of the chlorine atom, but by the scheme of the Anri reaction with the formation of ethyl -nitro--chloro--hydroxycarboxylates. The reaction proceeds via the intermediate formation of the zinc salt of ethyl chloronitroacetate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2729–2732, December, 1989. 相似文献
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The combustion behavior of Shuangya Mountain (SYM) coal dust has been investigated by means of TG in this paper. The reaction fraction can be obtained from isothermal TG data. The regressions of g(), an integral function of vs. t for different reaction mechanisms were performed. The mechanism of nucleation and nuclei growth is determined as the controlling step of the coal dust combustion reaction by the correlation coefficient of the regression, and the kinetic equation of the SYM coal dust combustion reaction has been established.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献