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21.
A highly active catalytic system for the carbonylation of meso- and terminal epoxides to β-lactones is described. The active catalyst, analogous to Coates' catalyst, is generated in situ from commercially available (TPP)CrCl and Co(2)(CO)(8). This practical system circumvents the preparation of air sensitive cobaltate salts, operates at low catalyst loadings, and allows the carbonylation of functionalized, sterically demanding and heterocyclic meso-epoxides. 相似文献
22.
An analytical study is performed on steady, laminar, and fully developed forced convection heat transfer in a parallel plate
channel with asymmetric uniform heat flux boundary conditions. The channel is filled with a saturated porous medium, and the
lower and upper walls are subjected to different uniform heat fluxes. The dimensionless form of the Darcy–Brinkman momentum
equation is solved to determine the dimensionless velocity profile, while the dimensionless energy equation is solved to obtain
temperature profile for a hydrodynamically and thermally fully developed flow in the channel. Nusselt numbers for the lower
and upper walls and an overall Nusselt number are defined. Analytical expressions for determination of the Nusselt numbers
and critical heat flux ratio, at which singularities are observed for individual Nusselt numbers, are obtained. Based on the
values of critical heat flux ratio and Darcy number, a diagram is provided to determine the direction of heat transfer between
the lower or upper walls while the fluid is flowing in the channel. 相似文献
23.
Murray SJ Müller-Bunz H Ibrahim H 《Chemical communications (Cambridge, England)》2012,48(50):6268-6270
A family of congested aryliodanes based on an anti-dimethanoanthracene backbone has been synthesised and two diaryliodonium salts and the iodyl derivative characterised by X-ray analysis. The latter shows a rare water coordination to the iodine(V) centre in the solid state. Applications of these reagents in functional group transfer reactions are reported. 相似文献
24.
Infusion-induced changes in the phenolics, antioxidant and colour propeties of St John’s wort (genus, Hypericum; specie, Hypericum perforatum L.) teas were studied for the first time. SJW teas prepared as three different infusions and coded as three (3?min), six (6?min) and twelve minutes (12?min). Investigation of phenolic compounds were performed by LC-DAD-ESI-MS/MS. A total of 18 phenolics including six chlorogenic acids, three phenolic acids, seven flavonoids and two naphtodianthrones were detected. It is worth noting that the phenolic profiles of St John’s wort teas were similar. However, the quantities of phenolic compounds individually and totally changed significantly for different infusion times. The highest total concentration was detected in 12?min (60.03?mg/L), followed by 6?min (54.81?mg/L) and 3?min (33.07?mg/L). The main difference for different infusion times was the hyperoside found as the most abundant phenolic only in 3?min samples. However, for 6?min and 12?minin infusions, chlorogenic acid was the most dominant phenolic compound. Similar to phenolics, antioxidant capacity of tea infusions showed an increasing trend with the extension of infusion time. 相似文献
25.
Hasim Yilmaz Ummihan Yilmaz 《高分子科学》2007,(3):245-252
In this study, the electrorheological (ER) behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil (SO) medium was investigated. Sedimentation stabilities of suspensions (c = 5 wt%) prepared using these talc powder powders were determined to be 78 days. The ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. The shear stress of talc powder suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and showed a typical shear thinning non-Newtonian visco-elastic behavior. Effects of frequency on the ER activity of talc powder/SO system were also investigated. 相似文献
26.
Gibson SE Ibrahim H Pasquier C Peplow MA Rushton JM Steed JW Sur S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(1):269-276
Metal isocyanides have been used and studied by organometallic chemists for many years and, as a result, they have a rich and interesting chemistry. The nature of metal-free isocyanides and the methods of making isocyanide complexes, however, has resulted in the vast majority of studies to date being performed with structurally simple isocyanides. We report here a new approach to the synthesis of isocyanide ligands that involves the reaction of a metal carbonyl ligand with the anion of a phosphoramidate. As phosphoramidates can be synthesised in one step from amines, our method means that the structural diversity of readily available amines, particularly chiral amines, can now be incorporated into isocyanide ligands. 相似文献
27.
Angle-resolved X-ray photoelectron spectroscopy and contact-angle measurements guided by a signal attenuation model are utilized to extract molar composition and anion enrichment in the vacuum interface of a binary ionic liquid mixture, having a common quaternary ammonium cation and two different anions. By using the intensity ratio of the F1s peaks belonging to the two different anions recorded at the full electron take-off angle range, from 0° to 80°, we have determined that only a fractionally covered and anion enriched surface layer can predict the AR-XPS data, which is also consistent with surface tension measurements. Moreover, the more bulky and non-spherical anion enrichment is evident even at the conventional and the so assumed bulk sensitive take-off angle of 0°. This methodology provides a surface enrichment factor of the molecular ions and clearly serves as an experimental evidence for recently debated surface layering and/or island structure in ionic liquid systems. 相似文献
28.
Surangkhana Martwiset Ozgur Yavuzcetin Michael Thorn Craig Versek Mark Tuominen E. Bryan Coughlin 《Journal of polymer science. Part A, Polymer chemistry》2009,47(1):188-196
Polyacrylates containing a different number of 1H‐1,2,3‐triazole groups per repeat unit have been synthesized via conventional free radical polymerization. These polymers were characterized by nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Proton conductivity measurements were made using impedance spectroscopy. Introduction of more than one triazole per repeat unit did not result in an increase in conductivity as there was an accompanying increase in glass transition temperature (Tg). A maximum conductivity of 17.5 μS/cm was obtained at 200 °C under anhydrous condition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 188–196, 2009 相似文献
29.
Titanium tetra-n-butoxide, Ti(OBun)4, and zirconium tetra-n-butoxide, Zr(OBun)4, were reacted with some well-known dioxime and monoxime ligands such as dimethylglyoxime (DMG), salicylaldoxime (SO) and
acetone oxime (AO). The structures of the resulting complexes have been determined by elemental analysis, i.r. and 1H-n.m.r. spectroscopy. The complexation ratio of both Ti(OBun)4 and Zr(OBun)4 was found to be 1:2 with DMG and SO. On the other hand, both 1:1 and 1:2 complexation ratios of the same metal alkoxides
were observed with the ligand AO. 相似文献
30.
哈斯穆 《新疆大学学报(理工版)》1998,15(2):78-85
在本文中,通过研究已经出版发行的《新疆维吾尔自治区小比例尺地图投影》的各种变形特点及其存在的精度问题,并设计出一种精度较高,适合于新疆实际情况的投影-斜轴等面积方位投影。经过严格计算,得出本投影的数据,在此基础上系统地分析地分析它的长度变形,优点和缺点等问题,以供给制图生产部门使用或参考。 相似文献