共查询到20条相似文献,搜索用时 15 毫秒
1.
LIU Yu-Gang FEI Chang-PeiInstitute of Chemistry Chinese Academy of Sciences Beijing ChinaCHAN Tak-HangDepartment of Chemistry McGill University Montreal PQ Canada HA K 《中国化学》1994,12(1):85-94
The alkylation reaction of guanine and N-acetylguanine with model compounds such as isopropyl bromide or 4-heptyl tosylate were studied. The reaction conditions such as temperature, solvent, base, and catalyst were examined for their effects on the reaction rate, and the yield and regioselectivity of the coupling reaction. The highest yield was obtained by using DMSO as the solvent. The reaction proceeded in a homogenous manner to give higher yield of 9-N and 7-N substituted product in a mole ratio of 1:1. The ratio could be raised to 2:1 if dibenzo-18-crown-6 was used as a catalyst. Using the above procedure, three carba-DHPG analogues bearing different 1'-C alkyl side chains were synthesized. 相似文献
2.
3.
Mark C. Finzel John Delong Martin C. Hawley 《Journal of polymer science. Part A, Polymer chemistry》1995,33(4):673-689
The bulk phase kinetics of an epoxy (DGEBA) /amine (DDS) thermoset have been studied using DSC, FTIR, and 13C-NMR. In the absence of catalyst, the reaction was found to involve a main exothermic reaction between epoxide and amine hydrogen and a side reaction between tertiary amine formed in the main reaction and epoxide. The main reaction was exothermic while the side reaction had no discernable exotherm. Etherification did not occur to any significant extent. Since only the main reaction is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydrogen were consumed at different rates as a way of following the side reaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above mechanism by identifying the formation of a quaternary ammonium ion/alkoxide ion pair as a reaction product of tertiary amine and epoxide. This mechanism has been successfully fit to a rate law valid over the entire extent of reaction. The rate constant for the epoxy/amine addition reaction was found to depend on hydroxide concentration (extent), reaction temperature, and glass transition temperature and included contributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not affect the overall system Tg. Both reactions were second order. The rate constants for the main reaction first increase with increasing extent due to autocatalysis by hydroxide before decreasing due to the diffusion limit caused by gelation and vitrification. © 1995 John Wiley & Sons, Inc. 相似文献
4.
[reaction: see text] The tandem intramolecular Michael-aldol reaction was studied as a tool for the construction of the C-ring of hexacyclinic acid. By changing the reaction conditions it was possible to selectively obtain either the kinetic or the thermodynamic product. Retro-aldol reaction and subsequent epimerization provides four individual cyclopentane derivatives that can be incorporated as building blocks in natural product syntheses. 相似文献
5.
Maxim A. Mironov Maria N. Ivantsova Maria I. Tokareva Vladimir S. Mokrushin 《Tetrahedron letters》2005,46(23):3957-3960
An accelerating effect of nucleophilic additives was revealed for the Passerini multi-component reaction. The influence of aqueous solutions on the reaction rate was studied in detail and the direct involvement of water in the bond-making step was attributed as the basis of an accelerating effect. Other nucleophiles were tested as alternatives to water; as a result N-hydroxysuccinimide is proposed as an accelerant of the Passerini reaction. 相似文献
6.
7.
8.
Häger M Olsson U Holmberg K 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6107-6115
A nucleophilic substitution reaction between 4-tert-butylbenzyl bromide and potassium iodide has been performed in oil-in-water microemulsions based on various C12Em surfactants, i.e., dodecyl ethoxylate with m number of oxyethylene units. The reaction kinetics was compared with the kinetics of reactions performed in other self-assembly structures based on very similar surfactants and in homogeneous liquids. The reaction was fastest in the micellar system, intermediate in rate in the microemulsions, and most sluggish in the liquid crystalline phase. Reaction in a Winsor I system, i.e., a two-phase system comprising an oil-in-water microemulsion in equilibrium with excess oil, was equally fast as reaction in a one-phase microemulsion. The reactions in microemulsion were surprisingly fast compared to reaction in homogeneous, protic liquids such as methanol and ethanol. The rate was independent of the microstructure of the microemulsion; however, the rate was very dependent on the type of surfactant used. When the C12Em surfactant was replaced by a sugar-based surfactant, octyl glucoside, the reaction was much more sluggish. The high reactivity in microemulsions based on C12Em surfactants is belived to be due to a favorable microenvironment in the reaction zone. The reaction is likely to occur within the surfactant palisade layer, where the water activity is relatively low and where the attacking species, the iodide ion, is poorly hydrated and, hence, more nucleophlic than in a protic solvent such as water or methanol. Sugar surfactants become more hydrated than alcohol ethoxylates and the lower reactivity in the microemulsion based on the sugar surfactant is probably due to a higher water activity in the reaction zone. 相似文献
9.
Prince AP Kleiber P Grassian VH Young MA 《Physical chemistry chemical physics : PCCP》2007,9(26):3432-3439
The heterogeneous chemistry of sulfur dioxide with CaCO(3) (calcite) aerosol as a function of relative humidity (RH) has been studied under isolated particle conditions in an atmospheric reaction chamber using infrared absorption spectroscopy. The reaction of SO(2) with calcite produced gas phase CO(2) as a product in addition to the conversion of the particulate carbonate to sulfite. The reaction extent was found to increase with elevated RH, as has been observed for the similar reaction with HNO(3), but much higher relative humidities were needed to significantly enhance the reaction. Mixed experiments in which calcite aerosol was exposed to both HNO(3) and SO(2) were also performed. The overall reaction extent at a given relative humidity did not appear to be increased by having both reactant gases present. The role of carbonate aerosol as an atmospheric sink for sulfur dioxide and particulate nitrogen and sulfur correlations are discussed. 相似文献
10.
A Taguchi robust design method with an L? orthogonal array was implemented to optimize experimental conditions for the biosynthesis of triethanolamine (TEA)-based esterquat cationic surfactants using an enzymatic reaction method. The esterification reaction conversion% was considered as the response. Enzyme amount, reaction time, reaction temperature and molar ratio of substrates, [oleic acid: triethanolamine (OA:TEA)] were chosen as main parameters. As a result of the Taguchi analysis in this study, the molar ratio of substrates was found to be the most influential parameter on the esterification reaction conversion%. The amount of enzyme in the reaction had also a significant effect on reaction conversion%. 相似文献
11.
Takuya Yoshikawa Teruoki Tago Ayaka Nakamura Aya Konaka Mitsushi Mukaida Takao Masuda 《Research on Chemical Intermediates》2011,37(9):1247-1256
Conversion of glycerol to useful chemicals was examined using a zirconia?Ciron oxide catalyst. An aqueous glycerol solution was used as feedstock, and the catalytic reaction was carried out in a fixed-bed flow reactor at 623?K under atmospheric pressure. Useful chemicals, for example propylene, allyl alcohol, carboxylic acids, and ketones, were obtained from the aqueous glycerol solution. The reaction was found to involve a series of consecutive reactions, with allyl alcohol and carboxylic acids as reaction intermediates which were converted to propylene and ketones, respectively. Moreover, the catalyst had high and stable activity in the reaction of a 50 wt% glycerol solution. 相似文献
12.
The reaction of aryldiazoacetates with enamines catalyzed by copper and rhodium complexes provided γ-ketoesters in good yields. Careful analysis of the crude reaction mixture revealed a substituted enamine as the primary product, which was hydrolyzed over silica gel to give a γ-ketoester as the final product. A reaction mechanism involving nucleophilic addition of an enamine to a metal carbene and subsequent hydrogen transfer was proposed. 相似文献
13.
The reaction between caprolactam and ethanol was performed in near-critical water. The primary product (ethyl-6-aminohexanoate) was identified by GC-MS. The influences of the reaction temperature, residence time, initial ratio (reactant/water), pH, and additives on the yields of ethyl-6-aminohexanoate are discussed. The results showed that the yield of ethyl-6-aminohexanoate could be as high as 98 % with SnCl2 as an additive in near-critical water. At the same time, the reaction between caprolactam and ethanol was estimated by a lumped kinetic equation as a second-order reaction in near-critical water, and the activation energy was evaluated according to the Arrhenius equation under acidic and basic conditions. Based on the results, the reaction mechanism between caprolactam and ethanol in near-critical water is proposed. 相似文献
14.
The condensation of glycerol and adipic acid was studied by 2D correlation spectroscopy in combination with MCR to identify spectral changes associated with this polymerization reaction and to describe the development of structure in the polymer. This biobased polymer is being evaluated for use as a controlled release matrix where the extent of reaction is a key performance parameter. A spectroscopic technique was sought to estimate the extent of reaction and guide product development. FT-IR spectra were collected as the reaction was performed on a temperature programmable ATR assembly fitted to a Bruker Tensor 27 spectrophotometer. The resulting time series was analyzed by 2D correlation spectroscopy. Correlation maps were used to identify bands related to the formation of the polymer and multivariate curve resolution (MCR) was applied to develop a model in terms of pure components. This combined technique offers a rapid method for sample analysis and facilitates the preparation of materials to a specified extent of reaction. 相似文献
15.
室温下FeCl3用于催化三聚异丁烯(TIB)与乙酸酐的酰化反应.发现FeCl3在所研究的催化剂中是最有效的.考察了FeCl3的用量、乙酸酐的用量和反应时间等因素对该酰化反应的影响.该反应产生一种混合物,其中两种产物是主要的.当反应在1 mmol TIB/15 mmol乙酸酐/0.50 mmol FeCl3/0.43 g氯仿和25℃下进行2 h时,生成的两种主要产物的总产率为69%.另外,反应在由沸石和FeCl3或P2O5组成的共催化剂存在下进行.该反应也用HY和H-β沸石之类的多相催化剂进行了尝试.负载FeCl3的HY和H-β沸石催化剂比FeCl3具有更高的催化活性和选择性. 相似文献
16.
17.
这里发现锰化合物能够催化芳香碳-氧键的还原断裂.就我们所知,目前还没有锰催化芳香碳-氧键断裂方面的报道.以二苯并呋喃为底物,对各种反应条件进行优化,得到的较佳反应条件为5% Mn(OAc)2,3当量Li-A1H4,140 ℃温度,四氢呋喃溶剂.在这个反应条件下,多种芳香碳-氧键能够发生还原断裂.甲醇钠的添加能够有效地促进二苯醚等底物的反应.对反应机理进行了初步研究,结果表明反应可能经历自由基过程. 相似文献
18.
以TiO2为载体负载双金属活性组分Ni-Co,采用浸渍法制备催化剂,用于糠醛催化加氢生成环戊酮和环戊醇的反应,并探讨了Ni-Co负载量、反应时间、反应温度、反应压力对其他产物的影响。通过XRD、BET、H2-TPR、SEM等表征方法对催化剂的构成及反应机理进行了讨论。结果表明,分别以一定比例负载金属活性组分制备的Ni-Co/TiO2和Co/TiO2催化剂,在最佳反应条件下环戊酮和环戊醇的生成率达到最高值,分别为53.4%和17.1%。 相似文献
19.
本文以纳米TiO2为催化剂,UV-LED(=365 nm)为紫外光源,在自制的恒温石英玻璃光催化反应器中成功实现了芳香醛的非均相光催化缩醛反应.以乙醇等作为溶剂和反应物,快速高效和高选择性地合成了苯甲醛二乙基缩醛(BDA).在光强为0.6 mw/cm2,苯甲醛初始浓度为0.05 mol/L,催化剂TiO2(P25)用量为5.0 g/L,反应时间为15 min的条件下,苯甲醛二乙缩醛的产率可达99.86%.研究表明,氧气的存在是顺利发生光催化缩醛反应的重要条件.反应液pH值、醇溶剂种类及苯环对位取代基等因素都会对光催化缩醛反应速率和产率产生影响.pH值及醇溶剂的pKa越小,缩醛反应速率越快.苯环上对位取代基会抑制缩醛反应的进行,其中供电子取代基相对吸电子取代基更有利于缩醛反应进行.结合实验,提出了光催化缩醛反应的机理. 相似文献
20.
Elementary chlorine was determined by a thermometric method using potassium iodide as reagent. The temperature rise corresponding to the heat of reaction was proportional to the chlorine content. Iodine formed in the reaction was also determined with sodium thiosulphate. The heat of the chlorine-iodide reaction is about five times that of the iodine-thiosulphate reaction. Direct determination with potassium iodide is simpler and more rapid than the indirect one. 相似文献