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用无梯度反应器在1.1MPa,628K到713K范围内研究了低浓度乙烯和苯在ZSM-5催化剂上烷基化反应的动力学规律.实验发现,乙烯的转化速率与苯分压无关;苯生成乙苯的选择性随苯分压增加而增高,但与乙烯分压无关.实验结果清楚地表明;乙烯在活性位上的吸附是反应的控制步骤;苯的吸附属弱吸附,吸附粒子既不成为活性分子,也不影响乙烯的吸附,但有效地阻止了乙烯的双分子聚合反应,使烷基化反应顺利进行. 相似文献
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Two analytical procedures based on the generation of volatile tributyltin derivatives, their separation by headspace solid-phase microextraction (HS SPME) and subsequent determination using plasma optical emission spectrometry (OES) have been developed for the selective determination of trace tributyltin (TBT) in the presence of other butyltins and inorganic tin in sediments without the use of chromatography. A microwave-assisted leaching of tin compounds from the sediment using 25%v/v acetic acid is applied for sample pretreatment. The first method takes advantage of TBT chloride releasing from the lecheate after adding 3 M hydrochloric acid, and subsequent separation of the analyte by HS SPME using Carboxen-poly(dimethylsiloxane) (CAR/PDMS). The second method involves the use of masking agents, namely ethylenediaminetetraacetic acid (EDTA) and diphenylcarbazone (DFC), which form stable chelates with monobutyltin (MBT) and dibutyltin (DBT), respectively, followed by the ethylation of tributyltin at pH 5 using sodium tetraethylborate (NaBEt4) solution. The final concentration of NaBEt4 is 0.05%w/v. The parameters affecting the TBT derivatisation and separation by HS SPME have been optimised including the selection of SPME fibre coating (PDMS, CAR/PDMS), the amount of masking agents and NaBEt4 added, sorption time (2–40 min) and sorption temperature (25–60°C). Higher sensitivity and robustness are attained with the method involving ethylation derivatisation, leading to the limit of detection (LOD) of 3 ng L?1. The selective release of TBT is observed from aqueous solutions, where the concentrations of MBT and DBT were in 2–50-fold excess to TBT. The SPME-TD-MIP-OES methods have been validated against several certified reference materials (CRMs), including SOPH-1 marine sediment, PACS-2 marine sediment and BCR 646 freshwater sediment. 相似文献
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Isotope ratio measurements characterizing 202Hg/200Hg in NIST SRM 3133 Mercury Standard Solution were undertaken by multicollector inductively coupled plasma mass spectrometry
employing NIST SRM 997 Tl for mass bias correction by use of the slope and the intercept obtained from a natural logarithmic
plot of each session of measurements of 202Hg/200Hg against 205Tl/203Tl. The calculated value of 1.285333 ± 0.000192 (mean and one standard deviation, n = 40) for the mass bias corrected 202Hg/200Hg was then used for mass bias correction of other Hg isotope pairs. Ratios of 0.015337 ± 0.000011, 1.68770 ± 0.00054, 2.3056 ± 0.0015,
1.3129 ± 0.0013, 2.9634 ± 0.0038, and 0.67937 ± 0.0013 (expanded uncertainty, k = 2) were obtained for 196Hg/198Hg, 199Hg/198Hg, 200Hg/198Hg, 201Hg/198Hg, 202Hg/198Hg, and 204Hg/198Hg, respectively. Reduction of Hg(II) to Hg0 in solutions of SRM 3133 was then undertaken using SnCl2, NaBH4, UV photolysis in the presence of formic acid, and ethylation of Hg(II) using NaBEt4. These reactions induced significant isotope fractionation with maximum values of 1.17 ± 0.07, 1.08 ± 0.09, 1.34 ± 0.07, and
3.59 ± 0.09‰ (one standard deviation, 1SD, n = 5) for δ
202/198Hg relative to the initial isotopic composition in the solution following 85–90% reduction of the Hg by SnCl2, NaBH4, UV photolysis, and ethylation with NaBEt4, respectively. Mass-dependent fractionation was found to be dominant for all reduction processes.
Figure Mass dependence of fractionation for all samples from Hg fractionation experiments using NaBEt4. Solid lines are the theoretically predicted MDF based on δ′ 202/198
Hg using equation 7. Error bars displayed are one standard deviation of the mean of 5 measurements of each sample 相似文献
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Oleg Kulinkovich Vladimir Isakov Dzmitry Kananovich 《Chemical record (New York, N.Y.)》2008,8(5):269-278
Interaction of titanium(IV) isopropoxide with ethylmagnesium bromide and its higher homologs leads to the generation of alkoxytitanacyclopropane species, which are able to act in the reactions with unsaturated compounds as 1,2‐dicarbanionic alkylating agents. The present review is focused on the processes of intermolecular regio‐ and stereoselective alkylation of carboxylic esters and allylic alcohol derivatives with alkoxytitanacyclopropane reagents. The oxophilicity of the titanium atom and its tendency to form sterically crowded ate complexes are probably the main factors providing a high level of selectivity of these transformations. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 269–278; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20155 相似文献
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Otis Evans Peter Kauffman Anne P. Vonderheide Larry J. Wymer Jeffrey N. Morgan 《Microchemical Journal》2009,92(2):155-164
The concurrent determination of pesticidal and non-pesticidal organotin compounds in several water matrices, using a simultaneous in situ ethylation and liquid–liquid extraction followed by splitless injection mode capillary gas chromatography with pulsed flame photometric detection, is described. The speciation analysis of nine organotin compounds includes low molecular weight–low boiling (non-pesticidal) and high molecular weight–high boiling analytes (pesticidal) of significant environmental interest. The minimum time for sodium tetraethylborate alkylation, using mechanical agitation, is determined to be 15 min in order to ensure the complete derivatization of the entire list of analytes. The utilization of a “hot needle” and a rapid injection rate is shown to be an efficacious means to eliminate “mass” or “needle” discrimination when determining the mixture of organotin compounds. Method detection limits are calculated to be in the low ng L− 1 range. The final method is applied to various water samples; storm water from the Cincinnati area demonstrated low native levels of three of the organotin compounds. 相似文献
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Study of the catalytic ethylation of p-t-butyltoluene in the presence of organosodium compounds, and of toluene in the presence of organopotassium compounds, was carried out at an ethylene pressure of 40 bar. Various yields of different products were obtained after 23 h of reaction in the presence of different tertiary polyamines used to complex and solubilize the organoalkali compounds. A higher initial ethylation rate was observed in the presence of organosodium than in the presence of organopotassium species. However, the thermal stability of organopotassium species being higher, much higher yields were observed in their presence in catalytic ethylation reactions than those observed previously. The results obtained concerning metallation or ethylation of hindered alkylaromatics may be interpreted by an anionic mechanism and the activation by a steric effect. 相似文献