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361.
Alajos Grün Mátyás Milen Tamás Földesi Péter Ábrányi-Balogh László Drahos 《合成通讯》2013,43(11):1491-1498
Twenty-five amides were synthesized in almost quantitative yields by microwave-assisted condensation of arylacetic acids and 2-aryl-ethylamines under solventless conditions. The N-arylethyl-arylacetylamides are intermediates of the corresponding isoquinoline derivates. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
362.
St. Bóbr 《Mathematische Zeitschrift》1921,10(1-2):1-11
Ohne Zusammenfassung 相似文献
363.
A method is suggested for the determination of submicrogram Cd in quantities by isotope dilution, using substoichiometric extraction into dithizone in chloroform. The applicability of the method was tested in biological samples. Extraction was carried out from a sodium acetate buffer betweenpH 9.7 and 12.0. With amounts of 0.2 μg of Cd, the S.E. was not greater than 0.01 μg. This method is suitable for large scale analysis of trace amounts of Cd in biological materials. 相似文献
364.
Ab initio conformational maps for methoxyethoxymethane (MEM) in both the gas phase and aqueous solution have been constructed using two different approaches. The results obtained allow us to conclude that a rigid conformational map is able to predict the regions of the minima, in the potential energy surface of MEM, in full agreement with those found in the relaxed conformational map, in both phases studied. This is a good indication that ab initio rigid conformational maps may be reliably used to sort the stablest conformers of disaccharides in aqueous solution. Besides that, in the MEM case, the solvation effects do not give rise to any new local minimum in its potential energy surface, but just change the relative energies of the stablest conformers found in the gas phase. This may be an indication that even in aqueous solution the anomeric effect is still the determinant effect defining the conformation of the molecule.Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail 相似文献
365.
R?mulo A.?Ando Cristiano?Raminelli Wagner J.?Barreto Keiko?TakashimaEmail author 《Monatshefte für Chemie / Chemical Monthly》2003,134(10):1321-1331
Summary. The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303K by following the formation of vanadium(IV) spectrophotometrically at 760nm. The oxidation reaction displays fractional order dependence with respect to both the -hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.Received April 8, 2003; accepted May 10, 2003
Published online September 18, 2003 相似文献
366.
Michael G.S. Londesborough Tomáš Jelínek Bohumil Štíbr Michael J. Carr 《Journal of organometallic chemistry》2005,690(11):2835-2839
The reaction of the hypho-[6,7-C2B6H13]− anion (1) with nickelocene and an excess of ‘proton sponge’ (1,8-bis-(dimethylamino-naphthalene)) in boiling acetonitrile leads to the formation of a pair of isomeric trimetallic nickel-boron clusters, [6,7,8-(CpNi)3-1-CB5H6] (2) and [6,7,8-(CpNi)3-2-CB5H6] (3), in a combined yield of 55%. Isomer (2) had been previously prepared from nido-2-CB5H9 but in much lower yield. Isomer (3) is without precedent and has been characterized using multi-nuclear NMR spectroscopy and mass spectrometry. Isomer (3) undergoes conversion to (2) via heating in boiling toluene. In addition to this isomeric pair, an interesting nido dimetallacarborane of constitution [6,6′-(CpNi)2-7,7′-C2B6H8] (4) has been isolated from the same reaction in 5% yield and characterized by single-crystal X-ray diffraction analysis. 相似文献
367.
Amarildo Otavio?Martins Edson Luiz?da Silva Mauro C. M.?Laranjeira Valfredo T.?de FávereEmail author 《Mikrochimica acta》2005,150(1):27-33
This work describes the application of chitosan – chemically modified with 8-hydroxyquinoline – in a simple and efficient preconcentration system using flow injection flame atomic absorption spectrometry (FI-FAAS) for the determination of Pb2+ ions. The efficiency of the chelating resin and the accuracy of the proposed method were evaluated by the metal ion recovery technique in samples of mineral water, potable water and lake water. The recovery of Pb2+ ions from spiked solutions was less than 70% due to matrix effects, which were eliminated by addition of Ba2+ metal ions, resulting in recoveries of approximately 100% for all water samples. Ag+, Cd2+, Cu2+, Mn2+, Ni2+, Zn2+, Hg2+, Ca2+, Mg2+, Cr3+, Al3+ and Fe3+ metal ions were studied with respect to their interference with Pb2+ metal ion determination, and the chelating resin exhibited high selectivity for Pb2+ at pH 7. The analytical properties of merit were obtained using the parameters previously optimized. The method shows high precision with a relative standard deviation (R.S.D.) of 1.1% (n=7) for a solution containing 50µgL–1 of Pb2+ and a detection limit (L.O.D.) of 1.7µgL–1. 相似文献
368.
Bould J Jelínek T Barrett SA Coles SJ Hursthouse MB Thornton-Pett M Stíbr B Kennedy JD 《Dalton transactions (Cambridge, England : 2003)》2005,(8):1499-1503
Structurally characterised 17-vertex [(PMe2Ph)2PtB16H17Me] 3 is obtained, albeit in low yield, by platination of 16-vertex B16H20 1 using [PtMe2(PMe2Ph)2] under mild conditions. Platination has occurred on the {B10} subcluster of 1, interesting in that B16H20 itself deprotonates on the {B8} subcluster: the reference 16-vertex [B16H19]- anion 1a, prepared by deprotonation of 1 with 1,8-bis(dimethylamino)naphthalene, is also structurally characterised. [PtMe2(PMe2Ph)2] with 14-vertex B14H18 2 similarly gives a low yield of 15-vertex [(PMe2Ph)2PtB14H16] 5, of formulation and structure substantiated by DFT calculations. 相似文献
369.
Holub J Jelínek T Hnyk D Plzák Z Císarová I Bakardjiev M Stíbr B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(7):1546-1554
The reaction between the carborane arachno-4,6-C2B7H13 (1) and PCl3 in dichloromethane in the presence of a "proton sponge" (PS = 1,8-dimethylaminonaphthalene) resulted in the isolation of the eleven-vertex nido-diphosphadicarbaboranes 7,8,9,11-P2C2B7H, (2) and 3-Cl-7,8,11-P2C2B7H, (3-Cl-2) in yields of 54 and 7%, respectively. Replacement of the PS by NEt3 in the same reaction gave diphosphadicarbaboranes 2 and 3-CI-2 together with the isomeric species nido-7,9,8,10-P2C2B7H, (3) in yields of 28, 15 and 3%, respectively. The reaction between the isomeric carborane arachno-4,5-C2B7H13 (4) and PCl3 in dichloromethane in the presence of PS gave the asymmetrical isomer, nido-7,8,9,10-P2C2B7H, (5). along with the chloro derivatives 4-Cl-7,8,9,10-P2C2B7H8 (4-Cl-5) and 11-Cl-7,8,9,10-PC2B7,H8 (11-Cl-5) (yields of 21, 1 and 13%, respectively). The structures of the chlorinated derivatives 3-Cl2 and 11 -Cl-5 were determined by X-ray diffraction analysis. In addition, the structures of all compounds isolated were geometry-optimised and confirmed by comparison of experimental 11B chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G* method. The calculations also include the structure and 11B NMR shifts of the isomer nido-7,10,8,9-P2C2B7H9 (6) which has not yet been isolated. 相似文献
370.
Ferreira SL dos Santos WN Bezerra MA Lemos VA Bosque-Sendra JM 《Analytical and bioanalytical chemistry》2003,375(3):443-449
A system for on-line preconcentration and determination of lead by flame atomic absorption spectrometry (FAAS) was proposed. It was based on the sorption of lead(II) ions on a minicolumn of polyurethane foam loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM). The optimisation step was carried out using two-level full factorial and Doehlert designs for the determination of the optimum conditions for lead preconcentration. The proposed procedure allowed the determination of lead with a detection limit of 2.2 microg L(-1), and a precision, calculated as relative standard deviation (RSD), of 2.4 and 6.8 for a lead concentration of 50.0 and 10.0 microg L(-1), respectively. A preconcentration factor of 45 and a sampling frequency of 27 samples per hour were obtained. The recovery achieved for lead determination in the presence of several cations demonstrated that this procedure has enough selectivity for analysis of environmental samples. The validation was carried out by analysis of certified reference material. This procedure was applied to lead determination in natural food. 相似文献