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排序方式: 共有234条查询结果,搜索用时 15 毫秒
1.
Summary A porous polymer resin loaded with hydrous zirconium oxide (Zr-gel) was evaluated as a stationary phase for the liquid chromatographic separation of disubstituted aromatic compounds. The prepared Zr-gel was used to separate disubstituted phenols andortho-substituted benzoic acid derivatives in reversed-phase mode. The retention time of catechol was greater than those of other disubstituted phenols; this implies that the Zr-gel has specificity for the phenolic hydroxyl group. The retention behavior ofortho-substituted benzoic acid derivatives on the Zr-gel was also evaluated in reversedphase mode using buffer. Phthalic acid was specifically retained in the vicinity of pH 6.0, which has been regarded as the equal adsorbic point. Similar behavior was also observed for salicylic acid, although the retention time of salicylic acid was less than that of phthalic acid. It seems that the specific retention behavior of hydrous zirconium oxide is a result of complexation with ligands such as hydroxyl and carboxyl groups. The results of this study have revealed that the retention mechanism of hydrous zirconium oxide is a combination of ion exchange and interaction based on complexation with ligands. 相似文献
2.
Significant improvement in enantioselectivity and catalyst activity was achieved for the catalytic enantioselective Strecker reaction. Using a catalyst (1-2.5 mol %) prepared from Gd(OiPr)3 and d-glucose derived ligand 1, and in the presence of 2,6-dimethylphenol as an additive, high enantioselectivity was obtained from a wide range of ketoimines, including heteroaromatic and cyclic ketoimines. The new method was applied to an efficient catalytic asymmetric synthesis of sorbinil, a therapeutic agent for diabetic complications. 相似文献
3.
Hans-Detlev Gilsing Jürgen Angerer Dietrich Prescher 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1147-1155
Summary. The synthesis of two oxidized metabolites of bis-(2-ethylhexyl)-phthalate is described. The target structures were obtained
by esterification of the appropriate alcohol carrying a protected hydroxy group with phthalic anhydride, followed by deprotection
and further oxidation.
Received February 26, 2002. Accepted March 6, 2002 相似文献
4.
Anirban Kar 《Tetrahedron》2005,61(22):5297-5302
Starting from citraconic anhydride (13), a simple multistep (9-10 steps) synthesis of naturally occurring butyrolactones maculalactone A (3), maculalactone B (1), maculalactone C (2) and nostoclide I (4) have been described with good overall yields via dibenzylmaleic anhydride (20) and benzylisopropylmaleic anhydride (27). The two anhydrides 20 and 27 were prepared by SN2′ coupling reactions of appropriate Grignard reagents with dimethyl bromomethylfumarate (14), LiOH-induced hydrolysis of esters to acids, bromination of carbon-carbon double bond, in situ dehydration followed by dehydrobromination and chemoselective allylic substitution of bromoatom in disubstituted anhydrides 19 and 26 with appropriate Grignard reagents. The NaBH4 reduction of these anhydrides 20 and 27 furnished the desired lactones 21 and 29, respectively. The lactone 21 on Knoevenagel condensation with benzaldehyde, furnished maculalactone B (1), which on isomerization gave maculalactone C (2). Selective catalytic hydrogenation of 1 gave maculalactone A (3). The conversion of lactone 29 to nostoclide I (4) is known. 相似文献
5.
M. Jochum R. Bakry I. Wartusch C. W. Huck H. Engelhardt G. K. Bonn 《Chromatographia》2002,56(5-6):263-268
Summary This paper reports on the use of a polymer-based, strong anion-exchange stationary phase for rapid, selective and sensitive
analysis of physiological important mono-, di- and oligosaccharides by high-performance anion-exchange chromatography (HPAEC)
with pulsed amperometric detection (PAD) under alkaline conditions. The adsorbent was obtained by direct nitration of 3 and
5 μm, spherical non-porous highly cross-linked, styrene-divinylbenzene copolymer (PS-DVB) beads, followed by reduction of
superficially introduced nitro groups with nascent hydrogen and quaternization of the resultant amino groups with iodomethane.
Extended exposure to high pressure and strong alkaline conditions did not have any untoward effect on mechanical stability
and chromatographic performance. A comparison of the 3 and 5 μm beads showed, that the synthesized 3 μm highly cross-linked
PS-DVB particles are the preferred phases for the separation of monosaccharides and the 5 μm particles are preferable for
the separation of oligosaccharides. To demonstrate the suitability for the analysis of complex samples, the optimized and
validated system was used for the determination of glucose, fructose and sucrose in apple juice and other soft drinks such
as Coca Cola. Finally, analysis within a few minutes without sample pretreatment down to a lower limit of detection of 0.174–0.504
μg mL−1 at a linearity with R2>0.994 and a repooducibility higher than 98% further confirmed the efficiency of these polymeric sorbents. 相似文献
6.
An extremely short synthesis of 2,2-dimethyl-3-hydroxymethyl cyclopentanone 2 (R1 = R2 = Me), an advanced intermediate in the synthesis of the pheromone planococcyl acetate 3, is described. 相似文献
7.
A. Abouimrane K. Sbai K. El Kababi A. Lahmidi A. Atibi Serge Vilminot 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):605-619
The dehydration of ZnRb 4 (P 3 O 9 ) 2 ·;6H 2 O was investigated, between 25 and 600°;C, by TG-DTA, X-ray diffraction, IR. It leads, between 300 and 500°;C, to a mixture of long chain polyphosphates RbPO 3 and ZnRb 2 (PO 3 ) 4 which stays stable until its melting point. The IR (1400-30 cm m 1 ) and Raman spectra (1400-100 cm m 1 ) of ZnRb 4 (P 3 O 9 ) 2 ·;6H 2 O are reported and assignments of fundamental modes proposed and compared with theoretical results obtained via the MNDO method for P 3 O 9 ring with C s symmetry. (La déshydratation, sous pression atmosphérique, du cyclotriphosphate ZnRb 4 (P 3 O 9 ) 2 ·;6H 2 O, a ét´;e effectuée, entre 25 and 600°;C, par spectrométrie IR, diffraction des rayons X, ATG et ATD. Elle conduit, entre 300 and 500°;C, au mélange de polyphosphates RbPO 3 et ZnRb 2 (PO 3 ) 4 qui reste stable jusqu'à la fusion. Les spectres vibrationnels IR (1400-30 cm m 1 ) et Raman (1400-100 cm m 1 ) du sel étudié ont été interprétés dans le domaine des vibrations de valence et de déformation du cycle P 3 O 9 et comparés avec les résultats des calculs théoriques par la méthode MNDO pour un cycle isolé de symétrie C s .) 相似文献
8.
《Optimization》2012,61(1):117-135
A statistical model tor giobai optimization is constructed generalizing some properties ofthe Wiener process to the multidimensional case. A new approach, which is similar to the Branch and Bound approach, is proposed to the construction of algorithms based on statistical models. A two dimensional version of the algorithm is implemented, and test results are presented 相似文献
9.
L. E. Carpenter Ii R. A. Jacobson J. G. Verkade 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):475-479
Abstract The crystal and molecular structure of the strainless phosphite ester MeOP(OCH2)2C(CH2O)2POMe determined by x-ray means is reported. The methoxy groups are in axial positions on the chair-form-six-membered rings. 相似文献
10.
Cemil İbiş Zeliha Gökmen Nihal Yilmaz Bozkurt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2907-2914
Mono(thio)substituted dienes 1a-1b gave compounds 3a-c and 5d-g with piperazine and piperidine derivatives in dichloromethane. Compounds 8 , 9 , and 10 were obtained from the reactions of perchlorobutadiene ( 6 ) with 1,4-butanedithiol ( 7 ) in ethanol in the presence of sodium hydroxide. Compounds 12a-b , 13a-b were obtained from the reactions of perchlorobutadiene ( 6 ) with allylmercaptan (CH 2 =CH--CH 2 --SH) and mercaptoethanol (HO--CH 2 --CH 2 --SH). 相似文献