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61.
The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers) with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three room-temperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm(2)im][BF4], where bmim = 1-butyl-3-methylimidazolium and bm(2)im = 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration similar to that observed in methanol, suggesting a parallel behavior. The above reaction also was studied with 2-bromo-3-nitrothiophene, an ortho-like derivative able to give peculiar intramolecular interactions in the transition state, which are strongly affected by the reaction medium. 相似文献
62.
Di Noto V Piga M Giffin GA Quartarone E Righetti P Mustarelli P Magistris A 《Physical chemistry chemical physics : PCCP》2011,13(26):12146-12154
Polybenzimidazoles (PBIs) are among the polymers of choice to prepare membranes for high temperature polymer fuel cells. Poly-2,2'(2,6-pyridine)-5,5'-bibenzimidazole (PBI5N), doped with H(3)PO(4), and acid-doped PBI5N containing 10 wt% of imidazole-functionalized silica membranes were studied with thermogravimetric analysis, differential scanning calorimetry, dynamic-mechanical analysis, infrared spectroscopy, and broadband electric spectroscopy to examine the structure-property relationships. Key results show that: (1) doped PBI5N membranes show thermal decomposition starting at 120 °C, while pristine PBI5N is stable up to 300 °C; (2) the presence of filler increases the acid uptake and decreases the crystallinity of PBI5N; (3) the addition of phosphoric acid reduces the mechanical properties of the membrane, while the addition of filler has the opposite effect; (4) acid-doped membranes have conductivity values on the order of 10(-2)-10(-3) S cm(-1); and (5) membranes exhibit a Vogel-Tamman-Fulcher (VTF) type proton conduction mechanism, where proton hopping is coupled with the segmental motion of the polymer chain. Infrared spectroscopy combined with DFT quantum mechanical calculations was used to assign the experimental spectrum of PBI5N. 相似文献
63.
The Hall angle θ in three V samples (RRR = 80, 120, 140) and two Nb samples (RRR = 57, 66) has been measured in the mixed state in order to elucidate the transport properties in the intrinsic type-II superconductors with intermediate purity. 相似文献
64.
New 4'-methoxybenzyl-, 4'-methylbenzyl-, benzyl-, 3',5'-difluorobenzyl-, 3',5'-dichlorobenzyl-, and 4'-nitrobenzyl-armed monoazatrithia-12-crown-4 ethers were prepared by the reductive amination of monoazatrithia-12-crown-4 with the appropriate benzenecarbaldehyde in the presence of NaBH(OAc)3. Cold electrospray ionization mass spectrometry and X-ray crystallography show that silver complexes with armed monoazatrithia-12-crown-4 ethers bearing aromatic side arms with electron-donating groups or electron-withdrawing groups are coordination polymers and trimers, respectively. The structures of the silver complexes were strongly dependent on the strength of the CH...pi interactions, which are controlled by substituent effects on the aromatic side arms. 相似文献
65.
Renato Noto Paolo Lo Meo Michelangelo Gruttadauria Giuseppe Werber 《Journal of heterocyclic chemistry》1999,36(3):667-674
As a development of our previous work, we performed a kinetic study of the oxidative cyclization reaction of some 2,4-diaryl-substituted aldehyde thiosemicarbazones 1a-n induced by ferric chloride and by cupric perchlorate. The results of cyclization of 1a-n were compared to those of the corresponding 2-methyl derivatives. The kinetic data were analyzed by means of the Hammett's equation. 相似文献
66.
L.L. Noto S.S. Pitale J.J. TerblansO.M. Ntwaeaborwa H.C. Swart 《Physica B: Condensed Matter》2012,407(10):1517-1520
Surface chemical changes of CaTiO3:Pr3+ phosphor material and their effect on the red emission intensity of the 1D2→3H4 transition of Pr3+, upon electron beam irradiation are presented. Red emission at 613 nm was obtained upon probing the surface with a 2 keV electron beam. The surface chemical changes and Pr3+ red emission were monitored using an Auger Electron Spectroscopy (AES) and Cathodoluminescence (CL) spectrometer, respectively. The CL intensity decreased with a decrease in O on the surface at 1×10−8 Torr base pressure and decreased with an increase in O on the surface at 1×10−6 Torr O2. The X-ray Photoelectron Spectroscopy (XPS) revealed that CL degradation at 1×10−6 Torr O2 is due to the formation of CaO and CaOx as well as TiO2/Ti2O3 non-luminescent species on the surface. 相似文献
67.
Intramolecular oxa-conjugate cyclization of α,β-unsaturated thioesters under Br?nsted acid catalysis, inspired by biosynthesis of polyketide natural products, provides a variety of 2,6-cis-substituted tetrahydropyran derivatives with excellent diastereoselectivities. An added bonus of this methodology is that the product tetrahydropyrans could be readily elaborated to various derivatives by exploiting the unique reactivity of the thioester group. 相似文献
68.
K. Yokoyama T. Oka K. Noto 《Physica C: Superconductivity and its Applications》2011,471(21-22):901-904
A pulsed-filed magnetization (PFM) is an important technique for industrial applications of superconducting bulk magnets, and several advanced PFM methods are proposed to enhance the trapped field. In the well-known IMRA method, the channel through the magnetic flux is formed by the flux flow caused by heat generation when applying the strong pulsed-field, and the magnetic flux is made to penetrate into the bulk through the channel in the following pulse application. On the other hand, large applied field leads to large heat generation, and, therefore, the trapped field is decreased greatly.This paper proposes an effective magnetizing method in which the channel composed of magnetic field is artificially formed by field-cooling (FC) using a permanent magnet and the magnetic flux by PFM is induced to the channel. To confirm the validity of this method, the bulk was magnetized by FC using Nd–Fe–B magnets of the rectangular and the ring shapes, and thereafter, a pulsed-field of 6.2 T was applied. As a result, the trapped field of the bulk magnetized by FC using the ring magnet was increased by about 20–25% as compared with that of the conventional PFM, and, moreover, it was observed that the channel was formed partially by measurement of the magnetic field distribution. 相似文献
69.
Dr. Karel Jeřábek Prof. Marco Zecca Dr. Paolo Centomo Federico Marchionda Dr. Luca Peruzzo Dr. Patrizia Canton Dr. Enrico Negro Prof. Vito Di Noto Prof. Benedetto Corain 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(28):9381-9387
Hyper‐cross‐linked resins stemming from a gel‐type poly‐chloromethylated poly(styrene‐co‐divinylbenzene) resin (GT) have been investigated by a multi‐methodological approach based on elemental analysis, scanning electron microscopy, X‐ray microanalysis, and solvent absorption. The hyper‐cross‐linking of the parent resin was accomplished by Friedel–Crafts alkylation of the phenyl rings of the resins with the chloromethyl groups. This produced a permanent pore system comprising both micropores (<2.0 nm in diameter) and mesopores (2.2 nm). The chloromethyl groups that did not react in the hyper‐cross‐linking step were transformed into methylmercaptan groups and the latter were then converted into sulfonic groups by oxidation with hydrogen peroxide. By this procedure the extensive permanent porosity of the parent unsulfonated hyper‐cross‐linked polymer (HGT) was retained by the sulfonated polymer (HGTS). The final exchange capacity of HGTS was determined to be 0.36 mmol g?1. HGTS was easily metalated with PdII and the subsequent reduction of the metal centers with either aqueous sodium borohydride, formaldehyde, or dihydrogen produced three Pd0/HGTS nanocomposites. The metal nanoparticles had diameters in the 1–6 nm range for all the nanocomposites, as determined by TEM, but with somewhat different distributions. When formaldehyde was used, more than 90 % of the nanoparticles were less than 3 nm and their radial distribution throughout the polymer beads was quite homogeneous. These findings show that with this reducing agent the metal nanoparticles are generated within the pore system of the polymer matrix, hence their size is controlled by the dimensions of the pores of the polymeric support. 相似文献
70.
The purpose of this study is to clarify the existence of an ordered and large scale coherent motion in a turbulent plane thermal plume in a thermally-stable stratified fluid inside a comparatively large enclosure. First, the upper part of the thermal plume was carefully observed by a flow visualization. Secondly, a wave form of plume temperature variation was measured. Thirdly, a spectrum analysis was carried out on time series data of the thermal plume. Finally, physical characteristics were investigated on vortices in the thermal plume based on results of the wave form and the spectrum analysis of the plume temperature. As a result, the main conclusions are obtained as follows. (1) An existence of vortices near the upper part of the thermal plume was firstly found by careful flow visualization. (2) From the wave form of temperature variation and the spectrum analysis of the thermal plume, it was clarified that the vortices are generated in the transition state and are transported to the turbulent state. (3) The vortices are ordered and they behave as a large scale coherent motion in the turbulent thermal plume. 相似文献