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71.
研究了在三种固体超强酸催化下醛(酮)自身的羟醛缩合反应,系统考察了反应时间,催化剂用量等因素对反应的影响,优化了反应条件.同时,对该反应的溶剂效应进行了研究.结果表明,当催化剂用量为2 g/1 mol醛(酮),反应5 h,转化率可达40%,溶剂对该反应有明显的抑制作用.超强酸对各种醛都具有较好的催化活性,其催化醛类化合物自身缩合的转化率都在48%以上,选择性在95%以上,证明固体超强酸对该缩合反应有较好的催化活性和选择性. 相似文献
72.
The adverse effects of injection solvent strength on microbore packed column SFC band broadening are demonstrated and a solventless injection system that eliminates these effects is introduced. The injection system removes solvent in a GC-like manner using a retention gap and an on-column capillary GC syringe. The analyte is delivered to the analytical column in a solvent-free plug of supercritical fluid mobile phase. 相似文献
73.
In the previous paper(Ⅲ), the following equation of solvent effect in organic chemistry was suggested:
Ei=a﹒Ai(1-Va﹒VAi)+d﹒Di(1-Vd﹒VDi)+E0
Where Ei is a physical or chemical property of the substrate in the solvent i and E0 is that in n-hexane. Ai and Di are constants of electron acception and donation effect of the solvent i respectively. VAi and VDi are constants of electron acception and donation space effect of the solvent i respectively, a and d are the sensitivities of E of the substrate vs the change of Ai and Di. Va and Vd are the constants of electron acception and donation space effect of the substrate respectively. In IR spectra E could be substituted by the wavenumber(ν). Ai and VAi have been established for 18 organic solvents (n-C6H14, n-C7H16, cyclohexane, CCl4, Ph-Me, ClCH:CCl2, Et2O, CHCl3, C6H6, CH2Cl2, ClCH2CH2Cl, Ph-NO2, THF, 1,4-dioxane, Et-NO2. MeCO2Et, Me-NO2, Me-CN).
In this paper Di and VDi have been established for these solvents. The equation also has been tested by the νC-X(X=Cl, Br) of five alkylhalides (t-BuCl, n-C5H11Cl, t-BuBr, Et-Br, EtC(H)BrMe) and νC=O of three carboxyl compounds (t-BuCOMe, Me2CO, MHB) and seven organotin compounds [(Ph2MeSiCH2)3SnO2C-C6H4-X-p(X=H-, CH3-, CH3O-, NO2-, F-. Cl-, I-)].
The relationship (ν=ρ﹒σ+ν0) between νC=O of organotin compounds and Hammett constants(σ) of the substituted groups in different solvents was studied and a relationship betweenρ and Ai, VAi, Di, VDi of the solvents was found. 相似文献
Ei=a﹒Ai(1-Va﹒VAi)+d﹒Di(1-Vd﹒VDi)+E0
Where Ei is a physical or chemical property of the substrate in the solvent i and E0 is that in n-hexane. Ai and Di are constants of electron acception and donation effect of the solvent i respectively. VAi and VDi are constants of electron acception and donation space effect of the solvent i respectively, a and d are the sensitivities of E of the substrate vs the change of Ai and Di. Va and Vd are the constants of electron acception and donation space effect of the substrate respectively. In IR spectra E could be substituted by the wavenumber(ν). Ai and VAi have been established for 18 organic solvents (n-C6H14, n-C7H16, cyclohexane, CCl4, Ph-Me, ClCH:CCl2, Et2O, CHCl3, C6H6, CH2Cl2, ClCH2CH2Cl, Ph-NO2, THF, 1,4-dioxane, Et-NO2. MeCO2Et, Me-NO2, Me-CN).
In this paper Di and VDi have been established for these solvents. The equation also has been tested by the νC-X(X=Cl, Br) of five alkylhalides (t-BuCl, n-C5H11Cl, t-BuBr, Et-Br, EtC(H)BrMe) and νC=O of three carboxyl compounds (t-BuCOMe, Me2CO, MHB) and seven organotin compounds [(Ph2MeSiCH2)3SnO2C-C6H4-X-p(X=H-, CH3-, CH3O-, NO2-, F-. Cl-, I-)].
The relationship (ν=ρ﹒σ+ν0) between νC=O of organotin compounds and Hammett constants(σ) of the substituted groups in different solvents was studied and a relationship betweenρ and Ai, VAi, Di, VDi of the solvents was found. 相似文献
74.
Summary In this study, a rapid and efficient semi-micro extraction procedure is presented for the extraction of some higher n-alkanes
from water and soil samples. In the case of water samples n-hexane was used as the organic phase in a phase volume ratio (volume
of aqueous phase/volume of organic phase) higher than 285, while in the case of soil samples, extraction with n-hexane was
carried out in the presence of an excess of 2 M NaCl solution. The extraction rate from soil samples is very high and is better
than Soxhlet extraction, comparable with supercritical fluid extraction. High preconcentration factor in water samples allows
the limits of detection to be in the ng.mL−1 level with the use of gas chromatographic analysis. Flame ionization detector was used for monitoring the analytes. The obtained
recoveries of all studied compounds from both water and soil samples are higher than 90%. This method was successfully used
to determine some n-alkanes in municipal wastewater and contaminated soil. 相似文献
75.
Conversion of sulphur compounds in reduced, contaminated sediments that are brought in upland conditions may largely affect the potential mobility of heavy metal contaminants. We applied selected methods for the determination of total sulphur and sulphur fractions in a contaminated sediment in the reduced state and after gradual drying and oxidation during 1 month. Dry ashing, followed by ion chromatographic detection, was reliable for the determination of total sulphur. Good recoveries were obtained in both reference samples and spiked samples. Total sulphur was 14.5±0.6 g kg−1 relative to dry sediment. Wet chemical methods that involve the determination of acid-volatile, Zn–HCl-reducible, chromium-reducible, acetone-soluble and HI-reducible sulphur were used to estimate specific sulphur forms. Results for acetone-soluble sulphur were to high and not consistent with results for other fractions. Major part of sulphur in the sediment (90%) was inorganic. Sulphides were converted partially to sulphate and to intermediary oxidised sulphur compounds upon oxidation of the sediment. The results suggested that the intermediary oxidised sulphur pool in the reduced sediment (2.5 g kg−1) mainly consisted of pyrite, that was not converted during drying and oxidation. No significant changes in organic sulphur were detected. 相似文献
76.
Varughese M. Alexander 《Tetrahedron letters》2005,46(40):6957-6959
Bismuth(III) nitrate pentahydrate is found to be an efficient catalyst for the Pechmann condensation reaction of phenols and β-ketoesters under solvent-free conditions. The reaction protocol is simple and is followed by aqueous work-up leading to the formation of the corresponding coumarin derivatives in good yield and high purity. 相似文献
77.
G.A. Groß 《Thermochimica Acta》2005,432(2):229-240
A silicon chip device with two types of integrated platinum thin film resistors was applied for microcaloric measurements. It was shown that the device is capable of fast characterization of liquid evaporation behaviour and allows the determination of evaporation enthalpies for pure liquids and mixtures. The applicability was demonstrated for a wide range of solvents from nonpolar aliphatic solvents over polar organics to protic solvents (e.g. iso-octane, toluene, acetone, ethanol, methanol and water). The sample volumes were in the range of about 2-5 μL. The determination of transient times, in case of constant power mode, or the power integral over time was used for the fast estimation of binary liquid mixtures. Thermo-resistive measurements of 5 μL droplets of solvent mixtures like methanol/iso-propanol, ethanol/water, iso-octane/iso-propanol and iso-octane/1,4-dioxane showed significant changes in temperature characteristics and evaporation enthalpies in dependence on composition. The applied heating power was about 1 W, which corresponds to measurement times between a few seconds and a minute. 相似文献
78.
交联聚异丁烯酸甲酯型负载树脂的孔结构与分离稀土性能的关系 总被引:3,自引:0,他引:3
本文报导异丁烯酸甲酯型负载树脂的交联度、致孔剂组成和含量对负载树脂孔结构的影响.结果指出,良溶剂和劣溶剂按一定比例混合作为致孔剂,可制备不同孔结构的树脂.致孔剂量增加,树脂表观比重减小,而比表面积、孔体积与平均孔径均增加.交联度从10%增加到35%,表观比重和比表面积增加,而孔体积与平均孔径减小.增加致孔剂所含良溶剂的比例,树脂的表观比重、比表面积增加,而孔体积与平均孔径减小.已制备一系列不同孔结构的2-乙己基膦酸单2-乙己基酯(P507)负载树脂,比较了它们分离La、Ce、Pr、Nd的性能.结果表明,适当孔结构的负载树脂用于萃取色层分离稀土元素具有优良的分离性能. 相似文献
79.
The inducing method for preparing Ag-micelle solution with the use of mixed solvent/nonsolvent, and the morphological characterization of the generated metal–micelles were investigated and reported in this paper. In this method, an Ag containing metal chelate polymer (MCP) raw solution was preprepared by dissolving poly(vinyl acetate) (PVAc)–silver nitrate (AgNO3) MCP in conc. formic acid, and a mixed solvent of HCOOH/H2O with specific water composition was then added to induce the micellization of the MCP chain. The critical water concentration (CWC) that was needed for inducing the formation of the Ag-micelles, and the water concentration at which the flocculation of the Ag-micelles occurred in micellar solution, were studied by measuring the transmittance of the dilute MCP solution; the results showed that a long-lasting MCP solution with stable micelles might be prepared by using a H2O/HCOOH solvent of specific weight ratio 1:1.2. The effect of the AgNO3 concentration on the morphology of the Ag-micelles was also investigated by transmission electron microscopy (TEM). At AgNO3 concentration below 0.5 wt%, the Ag-micelles displayed a variety of core-shell structure; but as the AgNO3 concentration was increased to 1.0–2.0 wt%, micelles that had Ag-solid embedded in the micellar core were observed. 相似文献
80.
Summary The net solvent effect for several solute-solvent pairs has been calculated by using the solvophobic approach for describing the liquid chromatographic process. For the same solutes and solvents the net solvent effect has been experimentally measured by using graphitized carbon black columns in GC and HPLC. A comparison between the measured and calculated values made in terms of normalized free energy changes, indicates that the solvophobic theory is fairly adequate for predicting the sequence of solvent strength and provides a comprehensive explanation of the various interactions occurring in reversed-phase LC. A critical discussion of the deviations of the theory from the experimental data is also presented.Presented at the 14th International Symposium on Chromatography London, September, 1982 相似文献