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991.
An equilibrium-limited heterogeneous catalytic reaction, propene metathesis is suitable for process intensification via sorption enhanced reaction. In this work, we investigate the effect of catalyst/adsorbent configuration for propene metathesis in conjunction with pressure swing reaction. The catalyst and adsorbent configuration variations were defined in terms of packing heterogeneity index (PHI) and their effects were investigated experimentally and theoretically. Model predictions were tested against experimental data with variable PHI and adsorption/reaction conditions, including the absence of heterogeneity and of separation process. The product 2-butene was strongly adsorbed and retained by the intermediate adsorbent layers, thereby increasing reactant concentration in the reaction zone and enhancing conversion and rate of reaction in the subsequent layer. Model predictions were found to agree reasonably with experimental data and were used to elucidate the mechanism and optimizing principle for such reactors. 相似文献
992.
Metal‐Free Reduction of CO2 with Hydroboranes: Two Efficient Pathways at Play for the Reduction of CO2 to Methanol
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Christophe Das Neves Gomes Enguerrand Blondiaux Dr. Pierre Thuéry Dr. Thibault Cantat 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):7098-7106
Guanidines and amidines prove to be highly efficient metal‐free catalysts for the reduction of CO2 to methanol with hydroboranes such as 9‐borabicyclo[3.3.1]nonane (9‐BBN) and catecholborane (catBH). Nitrogen bases, such as 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD), 7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (Me‐TBD), and 1,8‐diazabicycloundec‐7‐ene (DBU), are active catalysts for this transformation and Me‐TBD can catalyze the reduction of CO2 to methoxyborane at room temperature with TONs and TOFs of up to 648 and 33 h?1 (25 °C), respectively. Formate HCOOBR2 and acetal H2C(OBR2)2 derivatives have been identified as reaction intermediates in the reduction of CO2 with R2BH, and the first C?H‐bond formation is rate determining. Experimental and computational investigations show that TBD and Me‐TBD follow distinct mechanisms. The N?H bond of TBD is reactive toward dehydrocoupling with 9‐BBN and affords a novel frustrated Lewis pair (FLP) that can activate a CO2 molecule and form the stable adduct 2 , which is the catalytically active species and can facilitate the hydride transfer from the boron to the carbon atoms. In contrast, Me‐TBD promotes the reduction of CO2 through the activation of the hydroborane reagent. Detailed DFT calculations have shown that the computed energy barriers for the two mechanisms are consistent with the experimental findings and account for the reactivity of the different boron reductants. 相似文献
993.
Effect of the sol–gel route on the textural characteristics of silica imprinted with Rhodamine B
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Cícero de Coelho Escobar João Henrique Zimnoch dos Santos 《Journal of separation science》2014,37(7):868-875
A series of silica xerogels that support Rhodamine B as a template were synthesized using distinct sol–gel routes, namely, acid‐catalyzed routes, a base‐catalyzed route, acid‐catalyzed with base‐catalyzed (two steps) hydrolytic routes, and a FeCl3‐catalyzed nonhydrolytic route. The extraction methods (thermal, Soxhlet, water washing, and ultrasound) were also evaluated. The resulting xerogels were characterized through porosimetry using nitrogen adsorption/desorption. The samples were further analyzed through small‐angle X‐ray scattering, Fourier transform infrared spectroscopy, and SEM. The preparation route affected the materials’ textural properties. Extraction was optimized using acid and two‐step routes. The acid route from Rhodamine B to Rhodamine 6G generated the highest selectivity factor (2.5). The nonhydrolytic route produced the best imprinting factor. Competitive adsorption was also used, from which the approximate imprinting factor was 2. The cavity shape generated during the production of the imprinted silica dictates the adsorption behavior, not the magnitude of the surface area. 相似文献
994.
Mauricio Gomes Constantino Milton Beltrame Jr. Gil Valdo José da Silva Julio Zukerman-Schpector 《合成通讯》2013,43(2):321-329
A 12-step synthesis of the natural product (+)-Artemisinin, very active against malaria, is described. (-)-Isopulegol, which already contains two of the asymmetric centers of (+)-Artemisinin in the correct absolute configuration, was used as starting material. 相似文献
995.
Robson M. Matos Luiz Carlos Gomes de Lima Edward de Souza Ana Lúcia Americano Barcelos de Souza Miriam Bernardes Gomes de Lima Délio Soares Raslan 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2859-2870
Herein we report synthetic routes for the preparation of 2-chloro-1,3,2-dioxarsenane 1 , O,O'-bis(5,5-dimethyl-1,3,2-dioxarsenane)-2,2-dimethyl-1,3-propanediol 3 , 2-chloro-1,3,2-dioxaphosphorinane 4 , and 2-fluoro-1,3,2-dioxaphosphorinane 5 . The new synthetic routes described here have the advantage to be simple, very clean and to lead to the desired compounds in very good yields. Compound 2-fluoro-1,3,2-dioxarsenane 2 also was prepared in good yield and is described here for the first time. Compounds 1-5 were fully characterized on the basis of NMR spectroscopic studies. Semi-empirical structural studies have been carried out and the results show that 1 and 2 exist as a mixture of two conformers, whereas only one conformer for 4 and 5 have been found. Variable temperature 1 H NMR studies reveal a fluxional behaviour for 1 and a mechanism for the inter-conversion between its two conformers is proposed. 相似文献
996.
Tânia Maria Monteiro Janaína Marques Rodrigues Eliane Cristina Pires do Rego Werickson Fortunato de Carvalho Rocha Juliana Swensson de Mattos Fernanda Figueiredo Nunes Valnei Smarçaro da Cunha Marcus Henrique Campino de la Cruz Vanderléa de Souza 《Accreditation and quality assurance》2013,18(3):197-206
Cachaça is the typical and genuine denomination for the sugar cane beverage produced in Brazil. It has an alcoholic content between 38 and 48 % by volume, at 20 °C, and is obtained from the distillation of fermented sugar cane juice with the possible addition of up to 6 g/L of sugar, expressed by sucrose. This paper aims to outline the approach taken for the certification of the mass fraction of individual alcohols and their associated uncertainties in a cachaça certified reference material (CRM) produced by the Organic Analysis Laboratory of the Chemical Metrology Division of Inmetro. The requirements of ISO Guide 31, ISO Guide 34 and ISO Guide 35 were followed for the certification. This included the assessment of the degree of homogeneity of the material, the short-term stability study to determine the transport conditions, the long-term stability study to establish the shelf life and storage conditions of the CRM and the characterization process. The certified values were determined by two analytical techniques: gas chromatography coupled to mass spectrometry and gas chromatography with flame ionization detection. In order to support the routine testing of cachaça, in helping analytical laboratories validate and standardize their methods, the certified reference material (CRM 02.1/10.003b) was developed and certified for the mass fractions of methanol (9.18 mg/100 g ± 0.82 mg/100 g), 2-butanol (4.15 mg/100 g ± 0.40 mg/100 g), 1-butanol (1.30 mg/100 g ± 0.18 mg/100 g), isobutanol (24.0 mg/100 g ± 1.0 mg/100 g) and 1-propanol (29.4 mg/100 g ± 1.3 mg/100 g) in a spiked cachaça. 相似文献
997.
Cristiane de A. Dias Henrique de Santana Marcos A. L. Nobre Mauro C. Lopes 《Journal of Solid State Electrochemistry》2013,17(7):1967-1976
A simple hybrid synthesis processing method was developed to synthesize γ-MnO2 nanocrystalline particles. The polyol method was modified by the addition of nitric acid in order to allow the synthesizing of single-phase Mn3O4 in a large scale. In the sequence, the acid digestion technique was used to transform Mn3O4 into γ-MnO2. Structural and morphological characterization was carried out by X-ray diffractometry, Infrared and Raman spectroscopy, thermogravimetric analysis, nitrogen adsorption isotherm, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge–discharge measurements. The synthesized material exhibits a specific capacitance of 125.1 F?g?1 at a mass loading of 0.98 mg?cm?2. The relation between structural features and electrochemical activity is discussed by comparing the synthesized material with commercial electrolytic manganese dioxide. 相似文献
998.
Ligia R. Gomes John Nicolson Low Ana S. M. C. Rodrigues James L. Wardell Camillo H. da Silva Lima Marcus V. N. de Souza 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(5):549-555
The compounds N′‐benzylidene‐N‐methylpyrazine‐2‐carbohydrazide, C13H12N4O, (IIa), N′‐(2‐methoxybenzylidene)‐N‐methylpyrazine‐2‐carbohydrazide, C14H14N4O2, (IIb), N′‐(4‐cyanobenzylidene)‐N‐methylpyrazine‐2‐carbohydrazide dihydrate, C14H11N5O·2H2O, (IIc), N‐methyl‐N′‐(2‐nitrobenzylidene)pyrazine‐2‐carbohydrazide, C13H11N5O3, (IId), and N‐methyl‐N′‐(4‐nitrobenzylidene)pyrazine‐2‐carbohydrazide, C13H11N5O3, (IIe), have dihedral angles between the pyrazine rings and the benzene rings in the range 55–78°. These methylated pyrazine‐2‐carbohydrazides have supramolecular structures which are formed by weak C—H...O/N hydrogen bonds, with the exception of (IIc) which is hydrated. There are π–π stacking interactions in all five compounds. Three of these structures are compared with their nonmethylated counterparts, which have dihedral angles between the pyrazine rings and the benzene rings in the range 0–6°. 相似文献
999.
Complete assignments of 1H and 13C NMR spectral data for 7,7′‐dihydroarylnaphthalene lignan lactones
Rosangela da Silva João Henrique Carvalho Batista Carine da Silva Maringolo Paulo Marcos Donate 《Magnetic resonance in chemistry : MRC》2009,47(6):523-526
In this article we present a complete 1H and 13C NMR spectral analysis of three 7,7′‐dihydroarylnaphthalene lignan lactones using modern NMR techniques such as COSY, HSQC, HMBC and NOE experiments. Complete assignment and homonuclear hydrogen coupling constant measurements were performed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
1000.
Maria Isabel Gomes Salema Ana Paula Barbosa-Povoa Augusto Q. Novais 《European Journal of Operational Research》2007
In this work the design of a reverse distribution network is studied. Most of the proposed models on the subject are case based and, for that reason, they lack generality. In this paper we try to overcome this limitation and a generalized model is proposed. It contemplates the design of a generic reverse logistics network where capacity limits, multi-product management and uncertainty on product demands and returns are considered. A mixed integer formulation is developed which is solved using standard B&B techniques. The model is applied to an illustrative case. 相似文献