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231.
Metal‐Free Catalyst for the Chemoselective Methylation of Amines Using Carbon Dioxide as a Carbon Source
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Dr. Shoubhik Das Felix D. Bobbink Prof. Dr. Gabor Laurenczy Prof. Dr. Paul J. Dyson 《Angewandte Chemie (International ed. in English)》2014,53(47):12876-12879
N‐methylation of amines is an important step in the synthesis of many pharmaceuticals and has been widely applied in the preparation of other key intermediates and chemicals. Therefore, the development of efficient methylation methods has attracted considerable attention. In this respect, carbon dioxide is an attractive C1 building block because it is an abundant, renewable, and nontoxic carbon source. Consequently, we developed a highly chemoselective, metal‐free catalytic system that operates under ambient conditions for the N‐methylation of amines. 相似文献
232.
Preparation and characterization of Mg-Al hydrotalcite-like compounds containing cerium 总被引:2,自引:0,他引:2
Hydrotalcite-like compounds (HTlcs) containing Mg(2+), Al(3+), and Ce(3+) in the hydroxide layer and with carbonate as charge-balancing anion have been prepared by a co-precipitation (at constant pH) method. The Al/Ce ratio in the final product depends on the concentration in the initial solution. The crystallinity of the layered materials decreases with the increase in cerium content, probably, due to the distortions introduced by the large difference in the ionic radii of the cations. All the synthesized materials were characterized by XRD, FT-IR spectroscopy and TG/DTA. The textural properties were determined from low-temperature nitrogen adsorption-desorption measurements. 相似文献
233.
Biosorption of Cr(VI) ions from aqueous solutions: kinetics, equilibrium, thermodynamics and desorption studies 总被引:2,自引:0,他引:2
Cr(VI) is a major water pollutant from industrial effluent whose concentration is to be reduced within the permissible limit. Present study reports a systematic evaluation of six different natural adsorbents for the removal of Cr(VI) from aqueous solutions in batch process. The adsorption kinetic data were best described by pseudo-second order model. The values of mass transfer coefficient for Cr(VI) adsorption indicated that the velocity of the adsorbate transport from the bulk to the solid phase was quite fast. The effective diffusivity of Cr(VI) removal for all the adsorbents were of the order of 10(-10) m(2)/s which suggested chemisorption of the process. The adsorption process was jointly controlled by film diffusion and intraparticle diffusion. Maximum monolayer adsorption capacities onto the natural adsorbents used were comparable to the other natural adsorbents used by other researchers. The thermodynamic studies and sorption energy calculation using Dubinin-Radushkevich isotherm model indicated that the adsorption processes were endothermic and chemical in nature. FT-IR studies were carried out to understand the type of functional groups responsible for Cr(VI) binding process. Desorption study was carried out with different concentration of NaOH solutions. Application study was carried out using electroplating industrial wastewater. 相似文献
234.
Debaki Ghosh Souradeep Basu Monisha Singha Joyee Das Prabuddha Bhattacharya Amit Basak 《Tetrahedron letters》2017,58(21):2014-2018
Three crescent shaped heterocycle-fused phenanthrene based systems 1–3 have been synthesized starting from benzene (or substituted benzene) 1,2-bis-propargyl alcohols. Bis-alkylation with propargylic bromides provided the key intermediate, the bis-propargyl bis-ethers. In spite of the possibility of many competing reactions, the latter underwent facile double Garratt-Braverman cyclization to provide compounds 1–3 in near quantitative yield, in a striking reaction involving the formation of four C–C bonds in a single step. Compounds 1–3 showed binding interaction with DNA, predominantly, via groove binding along with partial intercalation (combilexins). Molecular docking study supported the proposed binding modes. 相似文献
235.
Madhumala Ghosh Devkumar Das Chandan Chakraborty Ajoy K. Ray 《Micron (Oxford, England : 1993)》2010,41(7):840-846
This paper aims at introducing an automated approach to leukocyte recognition using fuzzy divergence and modified thresholding techniques. The recognition is done through the segmentation of nuclei where Gamma, Gaussian and Cauchy type of fuzzy membership functions are studied for the image pixels. It is in fact found that Cauchy leads better segmentation as compared to others. In addition, image thresholding is modified for better recognition. Results are studied and discussed. 相似文献
236.
237.
AC Conduction and Time–Temperature Superposition Scaling in a Reduced Graphene Oxide–Zinc Sulfide Nanocomposite
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Koushik Chakraborty Poulomi Das Sankalpita Chakrabarty Dr. Tanusri Pal Dr. Surajit Ghosh 《Chemphyschem》2016,17(10):1518-1523
We report, herein, the results of an in depth study and concomitant analysis of the AC conduction [σ′(ω): f=20 Hz to 2 MHz] mechanism in a reduced graphene oxide–zinc sulfide (RGO–ZnS) composite. The magnitude of the real part of the complex impedance decreases with increase in both frequency and temperature, whereas the imaginary part shows an asymptotic maximum that shifts to higher frequencies with increasing temperature. On the other hand, the conductivity isotherm reveals a frequency‐independent conductivity at lower frequencies subsequent to a dispersive conductivity at higher frequencies, which follows a power law [σ′(ω)∝ωs] within a temperature range of 297 to 393 K. Temperature‐independent frequency exponent ′s′ indicates the occurrence of phonon‐assisted simple quantum tunnelling of electrons between the defects present in RGO. Finally, this sample follows the “time–temperature superposition principle”, as confirmed from the universal scaling of conductivity isotherms. These outcomes not only pave the way for increasing our elemental understanding of the transport mechanism in the RGO system, but will also motivate the investigation of the transport mechanism in other order–disorder systems. 相似文献
238.
Ciprian Dragan Adrian Samuila Subhankar Das Dan Iancu Mihai Bilici Lucian Dascalescu 《Journal of Electrostatics》2009,67(2-3):184-188
The aim of this study is to refine the understanding of the tribo-electrostatic phenomena that can affect the efficiency of suction-type dilute-phase transport systems. The study was conducted with mm-size ABS-PC particles, a granular material originating from genuine information technology wastes. The tribo-charging process was modelled using the response surface method of experimental design. The controlled variables were the granular material feed rate and the aspirating air speed rate. The monitored variable was the charge imparted to a well-defined section of the duct and which is equal to the charge transferred to the particles passing through that section of the pneumatic transport system. An induction type sensor connected to an electrometer has been employed for the measurements. The data were processed by a virtual instrument developed in LabView. A commercial software package was employed for estimating the effects of the various factors and predicting the optimum operating conditions, which were then confirmed by a final experiment. 相似文献
239.
Venkata Reddy Regalla RamaKrishnam Raju Addada Venkat Swami Puli Abhishek S. Saxena Anindita Chatterjee 《Tetrahedron letters》2017,58(24):2344-2346
A short and efficient method for the stereoselective synthesis of Dendrodolide L has been developed from inexpensive and commercially available starting material. This convergent synthesis utilizes Jacobsen kinetic resolution, regioselective ring-opening of epoxide and Yamaguchi macrolactonization as key steps. 相似文献
240.
The stereoselective synthesis of (+)-goniodiol, a cytotoxic styryllactone, has been accomplished in 10 steps starting from inexpensive and readily available d-manitol and δ-gluconolactone involving the direct and straightforward reaction conditions of Grignard addition, chain elongation, and hydroboration, thus making the synthesis simple and convenient. 相似文献