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Proton NMR was used to study the complexation reaction of Li+ and Na+ ions with 15-Crown-5 (15C5) in a number of binary acetonitrile (AN)-nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 15C5 was fast on the NMR timescale and only a single population average 1H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of AN in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of the formation constants. In all the solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. Finally, the experimental results were compared with theoretical ones that were obtained from molecular modeling methods. Based on our results, it is most probable that Li+-15C5 in solvent stays in a rather nesting complex form with greater LogKf values, but Na+-15C5 forms a complete perching complex form with lower LogKf values. 相似文献
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Transport in Porous Media - Many processes in nature (e.g., physical and biogeochemical processes in hyporheic zones, and arterial mass transport) occur near the interface of free-porous media. A... 相似文献
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Joshaghani M Gholivand MB Ahmadi F 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(5):1073-1078
The complexation reaction between Cu(2+), Co(2+) and Ni(2+) metal cations with N,N'-bis(salicylidene)-1,2-phenylenediamine (salophen), in three nonaqueous polar solvents such as: acetonitrile (AN), dimethyl sulfoxide (DMSO), methanol (MeOH) and two binary mixtures of AN:DMSO and AN:MeOH at 25 degrees C were studied by spectrophotometric and conductometric methods. All investigated metal ions form 1:1 ML complex which their stability constants were determined and increase as Irving-Williams stability order of Co(2+)相似文献
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A novel potentiometric zirconium - PVC matrix membrane sensor incorporating bis(diphenylphosphino) ferrocene as an electroactive material and tris(2-ethylhexyl)phosphate as solvent mediator is described. In mixed acetate buffer solution of pH 4.8, the sensor displays a rapid and linear response for zirconium ion over the concentration range 1.0 × 10−1 to 1.0 × 10−7 mol L−1 with a good slope of 59.7 ± 0.3 mV per decade and detection limit 1.8 × 10−8 mol L−1. The best performance was obtained with membrane composition 33% PVC, 65% TEHP, 1% NaTPB and 1% ionophore. The proposed electrode revealed excellent selectivity for zirconium ion over a wide variety of alkali, alkaline earth, transition and heavy metal ions and could be used in a pH range of 4.15-7.8. The electrode was applied for at least 1 month without any considerable divergence in the potential responses. The practical utility of the electrode has been demonstrated by its use as an indicator electrode in the potentiometric titration of zirconium ions with sodium fluoride and in determination of zirconium ion in some alloy, tape and waste water samples. 相似文献
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Mohsen Irandoust Mohammad Joshaghani Ezzat Rafiee Mahbubeh Pourshahbaz 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(4):855-859
The complexation reaction between palladium (II) acetate, and 1,1′-bis(diphenylphosphino)ferrocene, DPPF, was investigated in two different deuterated solvents CDCl3 and DMSO at various temperatures using 31P NMR spectroscopy. The exchange between free and complexed DPPF is slow on the NMR time scale and consequently, two 31P NMR signals were observed. At metal ion-to-ligand mole ratio larger than 1, only one 31P NMR signal was observed, indicating the formation of a 1:1 Pd2+–DPPF complex in solution. The formation constant of the resulting 1:1 complexes was determined from the integration of two 31P signals. The values of the thermodynamic parameters (ΔH, ΔS and ΔG298) for complexation were determined from the temperature dependence of stability constants. It was found that, in both solvents, the resulting complex is mainly entirely enthalpy stabilized and the ΔH compensates the TΔS contribution. 相似文献
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A series of insoluble salts of Keggin heteropoly compounds were prepared and used as catalysts for the Mannich-type reaction of benzaldehyde, aniline, and cyclohexanone in water. Among them, Cs2.5H0.5PW12O40 showed excellent catalytic activity. Effects of surfactant, catalyst loading and temperature were studied to introduce the best reaction condition. The optimized reaction conditions were extended to Mannich reaction of various aldehydes, ketones, and amines in water. This rapid procedure afforded structurally divers β-amino ketones with major anti diastereoselectivity. Additionally, four new compounds were reported. The catalyst was recovered and reused for subsequent runs. 相似文献
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The sol-gel derived Co-Mn/TiO catalysts for light olefins production 《燃料化学学报》2014,42(2):212-218
In this research work,two 30%(Co-Mn)/TiO2catalysts were prepared using sol-gel(catalyst A)and coprecipitation(catalyst B)methods.The activity and selectivity to C2~4light olefins in Fischer-Tropsch synthesis(FTS)has been studied in a fixed-bed reactor under different operational conditions.These operational conditions were:temperature220~280℃,and total pressure from0.1~0.6 MPa.The optimum operating conditions were investigated after steady state.As the results shown,the catalyst A was more selective to C2~4olefins(58.7%in 260℃)and catalyst B was more selective to C5+hydrocarbons.Characterization of both catalysts was carried out by using X-ray diffraction(XRD),scanning electron microscopy(SEM)and N2adsorption-desorption measurements methods. 相似文献
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Ezzat Rafiee Akram Fakhri Mohammad Joshaghani 《Journal of heterocyclic chemistry》2013,50(5):1121-1128
Different Keggin‐type heteropolycompounds were used in Pechmann reaction to obtain biologically active coumarins. Effect of solvent, catalyst loading, and molar ratios of substrates was studied to introduce the best reaction condition. The optimized reaction condition was extended to Pechmann reaction of methylacetoacetate with various monohydric and polyhydric phenols. This rapid procedure afforded structurally diverse coumarins with high to excellent yields. Short reaction times, simple work‐up, and mild reaction conditions were advantages of this method. The optimized catalysts were reusable for four runs. 相似文献
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The kinetics of complex formation between palladium(II) acetate, and 1,1’-bis(diphenylphosphino)ferrocene, dppf, in two different deuterated solvents CDCl3 and DMSO-d6 were investigated using 31P NMR spectroscopy. The mole ratio and the 31P-chemical shifts in DMSO-d6 solution revealed the formation of an intermediate, which is gradually converted into the more stable [Pd(dppf)OAc)2] species with a dppf acting as a chelate ligand. In the chloroform solution however, the interaction of metal ion and the ligand resulted directly in the formation of [Pd(dppf)OAc)2] species with a chelating dppf. The rate constant for the complexation reaction was evaluated from computer fitting of the corresponding integration-time data. 相似文献