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排序方式: 共有130条查询结果,搜索用时 23 毫秒
1.
Palladium-containing zeolites catalyze the cycloisomerization of diethyl diallylmalonate to dimethylcyclopentenes. When the reaction is carried out in toluene, the performance of the palladium catalyst depends on the pore size of the zeolites. At 60 °C, palladium adsorbed on large pore size Beta zeolite (pore size ∼7.4 Å) is more active than medium pore size ZSM-5 (pore size ∼5.4 Å). This lower activity of ZSM-5 compared to Beta is attributable to the restricted diffusion of reagent and products through the ZSM-5 channels as compared to Beta zeolite. However, due to the gas-like diffusion characteristic of the supercritical state, the activity of ZSM-5 increases and becomes identical to that of Beta zeolite using supercritical CO2 as medium. 相似文献
2.
J. A. Munoz Leyva M. Callejón Mochón N. Moreno Diaz A. Sánchez Misiego 《Mikrochimica acta》1984,84(3-4):295-302
Summary Dimedone bisthiosemicarbazone monohydrochloride has been examined to evaluate its usefulness as a reagent for rapid and sensitive Spectrophotometric determination of chlorate (0.5–5.0 ppm) by oxidation of the reagent in 70% perchloric acid medium and measurement of the yellow product. The molar absorptivity at 417 nm is 1.86×104 l·mole–1·cm–1. The relative standard deviation is 1.6% for 2.5 ppm of chlorate.
Spektropbotometrische Bestimmung von Chlorat mit Dimedonbisthiosemicarbazon-monocblorhydrat (I)
Zusammenfassung Die Verwendbarkeit von I als Reagens für die rasche und empfindliche spektrophotometrische Bestimmung von 0,5–5,0 ppm Chlorat durch Oxydation von I in 70%iger Perchlorsäure und Messung des gelben Reaktionsproduktes wurde untersucht. Die molare Absorptivität bei 417 nm beträgt 1,86×104 l·mol–1·cm–1. Die relative Standardabweichung beträgt 1,6% für 2,5 ppm Chlorat.相似文献
3.
Jose R. Cabrero‐Antonino Dr. Antonio Leyva‐Pérez Prof. Dr. Avelino Corma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(35):11107-11114
The triflimide iron(III) salt [Fe(NTf2)3] promotes the direct hydration of terminal and internal alkynes with very good Markovnikov regioselectivities and high yields. The enhanced carbophilic Lewis acidity of the FeIII cation mediated by the weakly‐coordinating triflimide anion is crucial for the catalytic activity. The iron(III) metal salt can be recycled in the form of the OPPh3/[Fe(NTf2)3] system with similar activity and selectivity. However, spectroscopic and kinetic studies show that [Fe(NTf2)3] hydrolyzes under the reaction conditions and that catalytically less active Brønsted species are formed, which points to a Lewis/Brønsted co‐catalysis. This triflimide‐based catalytic system is regioselective for the hydration of internal aryl‐alkynes and opens the door to a new synthetic route to alkyl ketophenones. As a proof of concept, the synthesis of two antipsychotics Haloperidol and Melperone, with general butyrophenone‐like structure, is shown. 相似文献
4.
Multisite Organic–Inorganic Hybrid Catalysts for the Direct Sustainable Synthesis of GABAergic Drugs
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Dr. Antonio Leyva‐Pérez Dr. Pilar García‐García Prof. Dr. Avelino Corma 《Angewandte Chemie (International ed. in English)》2014,53(33):8687-8690
Multisite organic–inorganic hybrid catalysts have been prepared and applied in a new general, practical, and sustainable synthetic procedure toward industrially relevant GABA derivatives. The domino sequence is composed of seven chemical transformations which are performed in two one‐pot reactions. The method produces both enantiomeric forms of the product in high enantiopurity as well as the racemate in good yields after a single column purification step. This protocol highlights major process intensification, catalyst recyclability, and low waste generation. 相似文献
5.
Luis D. Vargas Gustavo A. Chapela Orlando Guzmán Pedro Díaz Leyva Rodrigo Sánchez 《Molecular physics》2020,118(9-10)
We analyse by discrete molecular dynamics the self-assembly of SW trimer particles that contain a different number of attractive and repulsive spheres. They also have different geometries: linear, obtuse, rectangular and equilateral. We identify that some of these molecules exhibit liquid–vapour equilibria while others do not. For all of them, we show the morphological phase diagram built up from the different supra-molecular structures formed by each type of trimer. We simulated 14 different systems with a total of 321 states. The main features of the supra-molecular structures depend only on the composition and geometry of the trimer: triple SW trimers do not form supra-structures, double SW trimers and single SW trimers form monolayers, bilayers and worm-like micelles. The liquid–vapour coexistence properties are also exhibited. These trimers can be used to model complex amphiphiles beyond the standard ones, such as the Gemini and the Bola surfactants as well as colloidal particles. 相似文献
6.
7.
We examine the mutual synchronization of a one-dimensional chain of chaotic identical objects in the presence of a stimulus applied to the first site. We first describe the characteristics of the local elements, and then the process whereby a global nontrivial behavior emerges. A propensity criterion for networking is introduced, consisting in the coexistence within the attractor of a localized chaotic region, which displays high sensitivity to external stimuli, and an island of stability, which provides a reliable coupling signal to the neighbors in the chain. Based on this criterion, we compare homoclinic chaos, recently explored in lasers and conjectured to be typical of a single neuron, with Lorenz chaos. 相似文献
8.
Elisa Leyva Socorro Leyva-Ramos Rogelio Jiménez-Cataño Telma A. de Luna-Méndez Agobardo Cárdenas-Chaparro 《合成通讯》2017,47(6):604-608
Reaction of o-halonitrobenzenes with sodium azide under reflux of DMF/H2O gives benzofuroxans in one step in moderate to good yields. This is a faster methodology compared to the conventional procedure involving the preparation and subsequent pyrolysis of o-nitrophenyl azides. For comparison, the reaction was also performed under phase-transfer catalysis. 相似文献
9.
Introduction to focus issue: mesoscales in complex networks 总被引:1,自引:0,他引:1
10.
Francisco Eduardo de Sousa Filho João Hermínio da Silva Antônio Álamo Feitosa Saraiva Deyvid Dennys S. Brito Bartolomeu Cruz Viana Bruno Tavares de Oliveira Abagaro Paulo de Tarso Cavalcante Freire 《Brazilian Journal of Physics》2011,41(4-6):275-280
X-ray diffraction was combined with X-ray energy-dispersion, Fourier-transform infrared, and Raman spectroscopies to study the fossilization of a Cretaceous specimen of the plant Brachyphyllum castilhoi, a fossil from the Ipubi Formation, in the Araripe Sedimentary Basin, Northeastern Brazil. Among the possible fossilization processes, which could involve pyrite, silicon oxide, calcium oxide, or other minerals, we were able to single out pyritization as the central mechanism producing the fossil, more than 100 million years ago. In addition to expanding the knowledge of the Ipubi Formation, this study shows that, when combined with other experimental techniques, Raman spectroscopy is a valuable tool at the paleontologist’s disposal. 相似文献