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991.
The condensation of -substituted acetophenones with benzylidenebisurea in an acid medium has given 5-R-2-oxo-4,6-diphenyl-1,2,3,4-tetrahydropyrimidones. The analogous condensation of propiophenone forms 5-methyl-2-hydroxy-4,6-diphenylpyrimidine. The tetrahydro derivatives obtained are readily dehydrogenated to 5-R-2-hydroxy-4,6-diphenylpyrimidines.For part XX, see [1]. 相似文献
992.
M. Kabešová Z. Kozfšková M. Dunaj-Jurco 《Journal of Thermal Analysis and Calorimetry》1992,38(10):2273-2279
The crystal structures and thermal behaviour of [Cu(py)2(NCS)2] (at 293) and [Cu(4-Mepy)2(NCS)2] and 180 K) complexes have been compared with their different temperature behaviour. It was found that the thermal stability of coordinated thiocyanate ligands in the course of thermal decomposition depends not only on the properties of the ligand L, but it is related to the arrangement of the thiocyanatocopper chains in the crystal structures. 相似文献
993.
994.
S. N. Shkerin D. I. Bronin S. A. Kovyazina V. P. Gorelov A. V. Kuz'min Z. S. Martem'yanova S. M. Beresnev 《Journal of Structural Chemistry》2003,44(2):216-221
Electric conductivity, Raman spectra, and thermal expansion of La0.88Sr0.12Ga0.82Mg0.18O2.85 solid solution (LSGM1218) based on lanthanum gallate were studied at various temperatures, and Xray phase analysis was performed at room temperature. Dilatometric measurements showed that secondorder phase transitions occur at 775±10$ and 880± 20 K. The transition around 880 K is confirmed by Raman spectra and by a change in the conductivity activation energy in this temperature range. This transition is associated with a symmetry change in the oxygen sublattice. 相似文献
995.
Krayushkin M. M. Shirinian V. Z. Belen"kii L. I. Shadronov A. Yu. Vorontsova L. G. Starikova Z. A. 《Russian Chemical Bulletin》2002,51(8):1510-1514
The conditions for acylation of 2,5-dimethylthiophene with squaric acid dichloride were optimized, and 3,4-bis(2,5-dimethylthiophen-3-yl)cyclobut-3-ene-1,2-dione was obtained in good yield. X-ray diffraction analysis demonstrated that the by-product has the structure of 1a,1b-dichloro-5-(2,5-dimethylthiophen-3-yl)-3-hydroxy-4,5a-dimethyl-1b,4a,5,5a-tetrahydro-1aH-1-thiacyclopropa[a]pentalen-2-one. 相似文献
996.
997.
Z. M. Yaremko D. M. Nikipanchuk L. B. Fedushinskaya I. G. Uspenskaya 《Colloid Journal》2001,63(2):253-258
Based on an analysis of interparticle interaction in highly disperse powders, a parameter is suggested allowing one to evaluate the tendency of dispersed particles to the formation of aggregates, the aggregation coefficient. It was shown that the particles of metal oxide powders with radius smaller than 10 m are present in their aggregated state. It was found that redispersion of highly disperse titanium dioxide powder in the aqueous medium is incomplete. The incomplete redispersion may be caused by the roughness of particles and/or the formation of the regions of entrapped air that are not destroyed by capillary pressure. 相似文献
998.
Miguel B Bastida A Zúñiga J Requena A Halberstadt N 《Faraday discussions》2001,(118):257-68; discussion 295-314
A hybrid quantum-classical simulation of the vibrational predissociation of Br2...Nen, (n = 2-11) clusters in the B electronic state is carried out. The time-evolution of the reactants, products, and intermediates is analyzed by a kinetic mechanism consisting of three elementary steps: direct vibrational predissociation (VP), intramolecular vibrational redistribution (IVR), and evaporative cooling (EC). The importance of intramolecular vibrational redistribution followed by evaporative cooling relative to direct vibrational predissociation is shown to increase rapidly with increasing cluster size. Final product state distributions reveal that only one or less Br2 stretching quantum per neon atom is required in order to achieve complete dissociation (n quanta for n < or = 9 and n - 1 for n = 10 and 11). The proportion of available energy going into translation is proposed as a parameter to study the statistical behavior of the Van der Waals clusters. It is shown to depend only on the number of remaining degrees of freedom, a characteristic of a statistical behavior, for n > or = 3. 相似文献
999.
Jemal M Huang M Mao Y Whigan D Schuster A 《Rapid communications in mass spectrometry : RCM》2000,14(12):1023-1028
A sensitive, specific, accurate and reproducible liquid chromatography/electrospray tandem mass spectrometry method was developed and validated for the quantitation of fosinoprilat in 0.2 mL of human serum. The method employed acidification (with pH 4.0 sodium acetate buffer) of the serum samples to minimize the hydrolysis of the prodrug fosinopril to fosinoprilat prior to purification by automated 96-well solid-phase extraction. The required chromatographic separation of fosinoprilat and fosinopril was achieved isocratically on a Luna C8 analytical column (2 x 50 mm, 3 microm). The total run time was 2 min. The mobile phase contained methanol and water with 10 mM ammonium acetate. Detection was by positive ion electrospray tandem mass spectrometry. The standard curve, which ranged from 2.00 to 500 ng/mL, was fitted to a 1/x(2) weighted linear regression model. Fosinoprilat quality control (QC) samples used to determine the accuracy and precision of the method were prepared in human serum at concentrations of 5.00, 200, 400 and 1000 ng/mL. The assay accuracy was within 8% (dev). The intra- and inter-assay precisions were within 6 and 3% (RSD), respectively. Fosinopril QC samples used to gauge the rate of hydrolysis of fosinopril to fosinoprilat during the assay procedure were prepared in human serum at 500 ng/mL. The hydrolysis of fosinopril to fosinoprilat was =1%. This degree of conversion would cause little error in the analysis of post-dose serum samples since such samples are known to contain low levels of the prodrug compared with the drug. 相似文献
1000.
Wang D Schwinden MD Radesca L Patel B Kronenthal D Huang MH Nugent WA 《The Journal of organic chemistry》2004,69(5):1629-1633
The reaction of a variety of methyl esters with dimethylsulfoxonium methylide at 0-25 degrees C affords the chain-extended beta-keto dimethylsulfoxonium ylides. Subsequent treatment with hydrogen chloride in THF proceeds with loss of DMSO to afford the corresponding alpha-chloroketones. This sequence has been utilized to convert the methyl esters of CBZ-protected alanine and valine to the anti N-protected alpha-amino epoxides, which are important pharmaceutical intermediates. When the same protocol is applied to BOC-protected phenylalanine methyl ester, epimerization occurs so that the use of a more reactive aryl ester is required. This chemistry provides a practical route to alpha-chloroketones that avoids the use of toxic and explosive diazomethane. 相似文献