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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.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
3.
Alberti G Brunet E Dionigi C Juanes O de La Mata MJ Rodríguez-Ubis JC Vivani R 《Angewandte Chemie (International ed. in English)》1999,38(22):3351-3353
The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space. 相似文献
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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
7.
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
8.
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
9.
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
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