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排序方式: 共有161条查询结果,搜索用时 15 毫秒
1.
Josinira A. Amorim Osvaldo Chiavone-Filho Márcio L.L. Paredes Krishnaswamy Rajagopal 《Fluid Phase Equilibria》2007
High-pressure density data for cyclohexane + n-hexadecane mixtures at a wide temperature range was modeled with several classical equations of state (EOS) and correlative models. A modification for softening the co-volume and another for a volume scaling of the Peng–Robinson EOS (VS-PR) were proposed. The VS-PR model is able to correlate the pure component experimental data employing only five adjustable parameters, with root-mean-square deviation (RMSD) between calculated and experimental densities essentially within the experimental error. This result is superior to widely used approaches, i.e., a six parameter Tait model and six parameter volume translations (temperature and pressure dependent) for Peng–Robinson and Patel–Teja EOS. The VS-PR model also represents well the isobaric thermal expansion and the isothermal compressibility coefficients of the pure cyclohexane, a small naphthenic substance as well as a long chain n-alkane hydrocarbon, n-hexadecane. When modeling the mixture data, the use of VS-PR model of pure components along with the Redlich–Kister expansion, truncated at the first term, the density was correlated within a RMSD only 60% greater than the experimental error. The proposed model is able to accurately represent all the tested mixture data with a relatively small number of parameters. 相似文献
2.
The catalytic system methylaluminoxane (MAO) and bis(n-butylcyclopentadienyl)zirconium dichloride ((nBuCp)2ZrCl2) was immobilized on commercial silica, silica-alumina and aluminophosphate calcined at different temperatures. The properties of the supports were determined by using N2 adsorption-desorption isotherms at 77 K, FT-IR spectroscopy and SEM. After aluminium and zirconium impregnation, the catalysts were analyzed by ICP-AES, FT-IR and UV-vis spectroscopy. Ethylene polymerizations were carried out in a Schlenk tube at 70 °C and 1.2 bar of ethylene pressure. The polyethylene obtained was characterized by GPC, DSC and SEM.Catalysts supported on silica-alumina exhibited higher polymerization activity than those supported on silica and aluminophosphate. Besides, the activity of MAO/(nBuCp)2ZrCl2 catalytic system supported on silica-alumina and aluminophosphate decreased strongly with support calcination temperature, while remained almost constant when silica was employed as support. All these experimental features suggest a role of the support acid properties and hydroxyl group population in the generation of active polymerization species. 相似文献
3.
Garcia Ruano JL Alcudia A del Prado M Barros D Maestro MC Fernandez I 《The Journal of organic chemistry》2000,65(10):2856-2862
The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported. 相似文献
4.
Elisa Paredes 《Tetrahedron》2007,63(18):3790-3799
Thermal reactions between nitronaphthalenes and butadienes were studied. It was demonstrated that these reactions are capable of undergoing the normal electron demand Diels-Alder reaction, with a variety of dienes affording the phenanthrene derivatives. The influence of the extension and type of substitution was also discussed. When the electron-withdrawing activation of the naphthalenic nucleus or the donor properties of the dienes were not enough, N-naphthylpyrroles were detected as main product, suggesting that a competitive reaction would probably take place. The results clearly confirmed the dienophilic nature of nitronaphthalenic double bonds and provided an alternative procedure for phenanthrene derivatives and N-naphthylpyrroles' synthesis. The relative reactivity of the reactants and the viability of the reactions were discussed from a theoretical point of view. 相似文献
5.
6.
Francisco Faria M. Victoria Martín M. Carmen Paredes Amelia Tito 《Journal of heterocyclic chemistry》1987,24(5):1269-1274
Cycloaddition of diazomethane to pyrrolinones 1a,b,d,e affords only one regioisomer as a mixture of the epimeric pyrrolopyrazolines 2 and 2 ′,4-Halo derivatives 1f,g react with diazomethane to give the two possible regioisomers 2 and 3. The regio- and stereochemistry of the adducts is evidenced by the 1H-nmr data. The primary adducts originated from the halopyrrolinones suffer dehydrohalogenation to give aromatized products, which by further methylation give derivatives of type 7, 8, 10 and 11. 相似文献
7.
Villar-Rodil S. Paredes J. I. Martínez-Alonso A. Tascón J.M.D. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):37-43
The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to
get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main
stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and
morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR)
and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
9.
10.
Conjugated addition of alcohols to 9-hydroxy-and 9-methoxy-1, 4-anthraquinone, in the presence of a strong acid and an oxidant, affords the 2-alkoxy- and 3-alkoxy-substituted regioisomer, respectively. 相似文献