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431.
Stirring 4,7‐dimethoxy‐1‐indanol in chloroform at room temperature in the presence of a catalytic amount of p‐toluenesulfonic acid gave 4,7‐dimethoxy‐1(H)‐indene in quantitative yield. Other solvents, including benzene, which was the most frequently used one for this reaction, gave mostly polymeric materials. The new method was also effective for dehydration of other electron‐rich benzylic alcohols. 相似文献
432.
433.
α-[Mn(O2CMe)2]: a two-dimensional coordination polymer of the anhydrous manganese acetate polymorphs
Jian Lin Lei Yuan Dong-Wei Guo Gao Zhang Shi-Yan Yao Yun-Qi Tian 《Structural chemistry》2009,20(3):505-508
Abstract Two polymorphs of crystalline anhydrous manganese acetate, α-[Mn(O2CMe)2] (1) and β-[Mn(O2CMe)2] (2), were prepared under temperature-controlled solvothermal dehydration. X-ray single-crystal (and powder) diffractions revealed
that compound 1 crystallizes in monoclinic (a = 9.763(4), b = 4.972(2), c = 6.122(3) ?, β = 102.878(5)°, V = 289.7(2) ?3, Z = 4) space group P2/c. Although it was early prepared, its single crystal structure is firstly determined and known as a two-dimensional (2D) layer
structure; whereas, compound 2 demonstrates a three-dimensional diamondoid (dia-e) structure that people in its early X-ray single-crystal study was not aware of.
Graphical Abstract Anhydrous α-[Mn(O2CMe)2] was discovered in 1967, which two-dimensional layer structure is firstly determined by the X-ray single-crystal analysis.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
434.
Supported hydroxy sodalite (H-SOD) membranes were prepared on α-alumina disks using direct hydrothermal synthesis at 413 K for 3.5 h. The continuity of the membranes was verified using single gas permeation of He and N2 at ambient conditions. The membranes were impermeable to N2 and He, which validated absence of defects in the membrane structure. The membranes were used in dewatering several organic alcohol/water mixtures (organic alcohol being: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, and 2-pentanol). The influence of feed temperature (303–473 K), feed concentration (0–100 mol% alcohol in the feed), and absolute feed pressure (1.6–2.4 MPa) on the water flux were analyzed. The absolute feed pressure had no effect on the water permeance. The membrane exhibited a water/alcohol separation factor larger than 106 and showed excellent thermal, mechanical, and operation stability in continuously dehydrating a water/ethanol mixture (72 mol% water) by pervaporation at 473 K and 2.2 MPa for 125 h. The normalized water flux correlated well with the water feed concentration for the primary alcohols. Below 40 mol% water in mixtures with secondary alcohols the water flux was three orders of magnitude lower. The water mobility through the membrane had an activation energy of ∼15 kJ/mol. 相似文献
435.
P. J. Masset 《Journal of Thermal Analysis and Calorimetry》2009,96(2):439-441
The dehydration of LiCl·H2O was studied under inert helium atmosphere by DTA/TG for different heating rates. The dehydration of LiCl·H2O proceeds through a two step reaction between 99–110 and 160–186°C, respectively. It leads to the formation of LiCl·0.5H2O as intermediate compound. The proposed mechanism is:
and
Based on the temperature peak of the DTA signals the activation energies of the two reactions were determined to be 240 kJ
mol−1 (step 1) and 137 kJ mol−1 (step 2), respectively. 相似文献
436.
In the present study, the zinc‐catalyzed dehydration of a variety of amides with N‐methyl‐N‐(trimethylsilyl)trifluoroacetamide (MSTFA) as a dehydration reagent into the corresponding nitriles has been examined in detail. With the straightforward and commercially available zinc(II)triflate as the precatalyst and MSTFA, an excellent system has been established to afford nitriles in excellent yields and chemoselectivities. After investigation of reaction conditions and the scope and limitations, several efforts were carried out to understand the reaction mechanism. 相似文献
437.
Qing Yu Binbin Yu Hongmei Yang Xue Li Shuying Liu 《Journal of mass spectrometry : JMS》2012,47(10):1313-1321
For identification of ginsenoside enantiomers, electrospray ionization mass spectrometry (ESI‐MS) was used to generate silver complexes of the type [ginsenoside + Ag]+. Collision induced dissociation of the silver‐ginsenoside complexes produced fragment ions by dehydration, allowing differentiation of ginsenoside enantiomers by the intensity of [M + Ag ? H2O]+ ion. In the meanwhile, an approach based on the distinct profiles of enantiomer‐selective fragment ion intensity varied with collision energy was introduced to refine the identification and quantitation of ginsenoside enantiomers. Five pairs of enantiomeric ginsenosides were distinguished and quantified on the basis of the distribution of fragment ion [M + Ag ? H2O]+. This method was also extended to the identification of other type of ginsenoside isomers such as ginsenoside Rb2 and Rb3. For demonstrating the practicability of this novel approach, it was utilized to analyze the molar ratio of 20‐(S) and 20‐(R) type enantiomeric ginsenosides in enantiomer mixture in red ginseng extract. The generation of characteristic fragment ion [M + Ag ? H2O]+ likely results from the reduction of potential energy barrier of dehydration because of the catalysis of silver ion. The mechanism of enantiomer identification of ginsenosides was discussed from the aspects of computational modeling and internal energy. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
438.
439.
M. TunÇ H. ErŞahan S. Yapici S. Şolak 《Journal of Thermal Analysis and Calorimetry》1997,48(2):403-411
In the present study, the kinetic parameters of the thermal decomposition of ulexite were investigated by using TGA data. For the kinetic analysis, the Suzuki and Coats-Redfern methods were applied. It was determined that the process fits a first-order kinetic model, and the value of the activation energies and frequency factors decreased with decreasing particle size, which can be attributed to the increasing particle internal resistance to the escape of water as the grain size increases. The activation energy values were found to be 47.34–60.01 kJ mol–1 for region I and 0.225–1.796 kJ mol–1 for region II for the range of particle size fraction used. The frequency factors were calculated to be 9821.8–524.9 s–1 for region I and 3.05×10–44–2.807×10–5 for region II for the same conditions. 相似文献
440.
通过两因素四水平的正交试验,研究了罗丹明B吸光光度法测定粉煤灰中的Ca含量时,脱水温度及脱水时间对测定结果的影响,确定了最佳脱水温度及时间,并在此条件下进行了加标回收试验,其回收率为97.3%。 相似文献