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941.
Seema Agarwal 《European Polymer Journal》2004,40(9):2143-2152
Sm(III) complex was generated in situ by one-electron transfer reaction of SmI2 with MMA. The resulting Sm(III) complex was tried as ring opening polymerization (ROP) initiator for cyclic esters like ε-caprolactone (CL). The polymers were obtained in high yield with low polydispersity index (1.1-1.2). The system was also used for the synthesis of block copolymers. Structural characterization of the resulting polymers was done using 1D (1H, 13C, 19F) and 2D (1H-13C heteronuclear multiple quantum correlation (HMQC) and heteronuclear multiple-bond correlation (HMBC)) NMR spectroscopic techniques. 相似文献
942.
François P Touchard 《Tetrahedron letters》2004,45(28):5519-5523
The Horner-Wadsworth-Emmons reaction of both 1 (Still's reagent) and 2 (Ando's reagent) with aldehydes was studied. Tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1) was shown to be an efficient additive when the reaction was performed in THF at −78 °C. Selectivities close to 95% were obtained in the condensation of 1 with aromatic aldehydes. The use of a 5-fold excess of 18C6 in this reaction had already been reported. However, we have defined conditions in which only catalytic amounts are required. 相似文献
943.
The GC–MS characteristics of carboxylic acid esters prepared from fluorine-containing alcohols were compared to those of methyl esters. The GC retention of 2,2,2-trifluoroethyl (TFE) esters was less than, and 2,2,3,3,4,4,4-heptafluoro-1-butyl (HFB) esters was approximately equivalent to that of methyl esters. Mass spectra of TFE and HFB aliphatic esters show significantly more intense molecular and key fragment ions than those of methyl esters. Also, owing to their significantly higher molecular weights, TFE or HFB ester molecular ions and most fragment ions of interest occur at significantly higher m/z values than most potential interfering ions. Data for about 70 individual TFE and HFB esters are reported. Application of the methodology to a petroleum-derived carboxylic acid concentrate resulted in identification of straight chain, isoprenoid, methyl-substituted straight chain (2-, 3-, 5-,10-, 12-positions along chain), and dimethyl-substituted straight chain acids containing from 11 to 22 carbons. Benzoic acid and homologs with up to 3-carbons in alkyl substitutents were minor components in the sample. The procedure provided for forming TFE and HFB esters from free acids requires less time and effort than a previously reported method, while retaining its capability for achieving essentially quantitative conversion. Free hydroxyl groups in alcohols and phenols are converted to trifluoroacetate esters concurrently with formation of TFE/HFB carboxylic acid esters. The reaction products, including compounds with two functional groups (diacids, salicylic acid, etc.), chromatograph well on conventional nonpolar GC stationary phases. 相似文献
944.
Issa Yavari Farough Nasiri Loghman Moradi Hoorieh Djahaniani 《Tetrahedron letters》2004,45(38):7099-7101
Reaction of tert-butyl isocyanide with electron-deficient acetylenic esters in the presence of N1-[(Z)-1-benzoyl-3-oxo-3-phenyl-1-propenyl]-2-(2-furyl)-2-oxoacetamide leads to dialkyl 5-tert-butylamino-[2,2′]bifuranyl-3,4-dicarboxylates in moderate yields. 相似文献
945.
Summary. A comparative study of the transesterification of five representative chiral and achiral boronic esters with various structurally
modified diols was undertaken to qualitatively understand the factors influencing the relative stability of these boronic
esters. Several factors such as chelation, conformation, steric bulk of the substituents, size of the heterocycle, and entropy
influence the relative rate of transesterification as well as the stability of the boronic esters. Amongst these boronic esters,
pinanediol phenylboronic ester was found to be the most stable boronic ester whereas DIPT boronic ester appeared to be thermodynamically the least stable one. The transesterification with sterically hindered diols
was observed to be relatively slow, but afforded thermodynamically more stable boronic esters. Boronic esters derived from
cis-cyclopentanediols and the bicyclo[2.2.1]heptane-exo,exo-2,3-diols are relatively more stable. This study not only presents the qualitative picture of relative stability of various
boronic esters, but also provides helpful hints regarding the possible recovery of chiral auxiliaries. Many C
2-symmetric chiral auxiliaries, such as 2,3-butanediol, 2,4-pentanediol, DIPT, and cis-cyclohexane-1,2-diol, can be retrieved by simple transesterification of the corresponding boronic esters with commercial
inexpensive diols, such as pinacol, 1,3-propanediol, and neopentyl glycol.
This paper is dedicated to the memory of my mentor, the late Professor Herbert C. Brown (1912–2004). Professor Herbert C. Brown deceased on December 19, 2004. The work described herein was carried out at Purdue University during my stay as a post-doctoral
research associate 相似文献
946.
A novel, one-pot, three-component synthesis of 4H-pyrido[1,2-a]pyrimidines is described. The reactive 1:1 zwitterionic intermediate, formed by the addition of isocyanides to dialkyl acetylenedicarboxylates, was trapped by N-(2-pyridyl)amides to produce the title compounds under mild reaction conditions in good yields. 相似文献
947.
Karl-Dieter Müller H. Peter Nalik Ernst N. Schmid Heribert Husmann Gerhard Schomburg 《Journal of separation science》1993,16(3):161-165
Trimethylsulfonium hydroxide (TMSH) reproducibly converts fatty acids bound in, e.g., biomolecules such as phospholipids and/or glycerides, into the corresponding fatty acid methyl esters (FAMEs). The transesterification can be performed at room temperature in a fast single step reaction. Surprisingly, secondary alcohols and mycolic acid cleavage products (MACPs) are also released from mycobacteria under these conditions. The complex reaction mixtures containing FAMEs, MACPs, and secondary alcohols can easily be separated by high resolution temperature-programmed capillary GC. Different species of mycobacteria give rise to characteristic chromatographic patterns and the amount of lipids from a single colony of mycobacteria is sufficient for reliable identification of the bacteria. The profiles of the chromatograms match well those obtained from other sample preparation techniques. The TMSH method of identification of mycobacteria from the patterns of the gas chromatograms is faster and more sensitive than conventional methods, which also involve transesterification. The identification of mycobacterial species by microbiological culture techniques is difficult to perform and requires several weeks. 相似文献
948.
Li-juan Yang Xiao-dong Yang Shu Yang Jing-feng Zhao Hong-bin Zhang Liang Li 《Chemistry of Natural Compounds》2006,42(6):649-651
Two new benzoyl esters of glucose 1-O-(E)-4′-methoxybenzoyl-β-D-glucopyranose (1) and 1-O-(E)-4′-methoxybenzoyl-β-D-gluconic acid (2) were isolated from Lagotis yunnanensis, together with six previously known iridoid glucosides. The structures of these compounds were elucidated on the basis of
spectral analysis, including 2D NMR spectroscopy.
Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 529–530, November–December, 2006. 相似文献
949.
A method based on liquid-liquid extraction (LLE) and automated large volume injection (LVI)-GC-MS analysis was developed for the trace determination of phthalate di-esters in water samples at sub-g L–1 (ppb) levels. Strategies applied to reduce contamination include (i) careful selection of tools, glassware and solvents, (ii) systematic blank checks of the chromatographic system, glassware and solvents and (iii) frequent verifications of blanks during sequences. Background levels could be reduced to those present in the extraction solvent. For phthalates not present in the extraction solvent the limits of quantitation (LOQ) are 6 ng L–1 for di-methyl phthalate (DMP), 3 ng L–1 for benzylbutyl phthalate (BzBP) and 45 ng L–1 for the isomeric phthalate mixtures di-isononyl phthalate (DiNP) and di-isodecyl phthalate (DiDP). For the other phthalates, the LOQ was set at twice the blank (extraction solvent) level and are 20 ng L–1 for di-ethyl phthalate (DEP), 60 ng L–1 for di-isobutyl phthalate (DiBP), 80 ng L–1 for di-n-butyl phthalate (DBP) and 30 ng L–1 for bis-(2-ethylhexyl) phthalate (DEHP).Dedicated to Professor K. Jinno on the occasion of his 60th birthday 相似文献
950.
Summary As part of an on-going ASEAN+)-Canada Cooperative Programme on Marine Science, microwave-assisted solvent extraction has been employed for the extraction of six phthalate esters from marine sediment and soil samples. Five of the six esters studied are among the United States Environmental Protection Agency's list of top priority pollutants. The effects of extraction solvent, extraction temperature, duration of extraction and extraction volume on the mean recoveries of the six phthalate esters were quantitatively evaluated by means of an analysis of variance, followed by testing the differences among the level means for each condition with least significant difference method. Microwave-assisted solvent extraction allowed comparable or higher recoveries of the six phthalate esters (70.1–91.0%) in comparison with conventional soxhlet (65.5–89.5%) and sonication (64.6–88.6%). The precision of results by microwave-assisted solvent extraction was improved significantly compared to the conventional techniques. The microwave extraction system has many advantages over the soxhlet and sonication extraction, e.g., no laborious clean-up procedure, lower usage of hazardous organic solvent, and larger sample throughput. The technique has been employed for the analysis of native marine sediment and soil samples in Singapore. 相似文献