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Ether System (ether + system)
Selected AbstractsA Two-Step Procedure for the Preparation of Mono-Protected Bis-N-heterocyclic Alkyl Ether Systems.CHEMINFORM, Issue 19 2007Jianhua Chao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Efficient Heterogeneous Asymmetric Catalysis of the Mukaiyama Aldol Reaction by Silica- and Ionic Liquid-Supported Lewis Acid Copper(II) Complexes of Bis(oxazolines)ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2 2008S. Doherty Abstract Lewis acid complexes based on copper(II) and an imidazolium-tagged bis(oxazoline) have been used to catalyse the asymmetric Mukaiyama aldol reaction between methyl pyruvate and 1-methoxy-1-trimethylsilyloxypropene under homogeneous and heterogeneous conditions. Although the ees obtained in ionic liquid were similar to those found in dichloromethane, there was a significant rate enhancement in the ionic liquid with reactions typically reaching completion within 2,min compared with only 55,% conversion after 60,min in dichloromethane. However, this rate enhancement was offset by lower chemoselectivity in ionic liquids due to the formation of 3-hydroxy-1,3-diphenylbutan-1-one as a by-product. Supporting the catalyst on silica or an imidazolium-modified silica using the ionic liquid or in an ionic liquid-diethyl ether system completely suppressed the formation of this by-product without reducing the enantioselectivity. Although the heterogeneous systems were characterised by a drop in catalytic activity the system could be recycled up to five times without any loss in conversion or ee. [source] Anionic and ionic coordinative polymerization of ,-caprolactonePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2001Dr Cristina Stere Abstract The polymerization of ,-caprolactone initiated by two catalyst systems was studied: (1) carbazole-potassium in the presence of 18-crown-6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri-n-butyl-phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H - and 13C,NMR spectroscopy. Polyesters with the highest molecular weight (Mn,44 000 g/mol) were obtained for the polymerizations initiated by the carbazole-potassium/18-crown-6 ether system. The features of the polymerization initiated by the carbazole-potassium/18-crown-6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non-living. Copyright © 2000 John Wiley & Sons, Ltd. [source] Collision-induced dissociation studies of protonated ether,(H2O)n (n = 1,3) clustersJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2006Daniel J. Goebbert Abstract We have studied the protonated ether,(H2O)n (n = 1,3) complexes containing tetrahydrofuran, dimethyl, diethyl, dibutyl, and butylmethyl ethers using a flowing afterglow triple-quadrupole mass spectrometer. Collision-induced dissociation, CID, of all clusters with n = 1, 2 shows sequential water loss. The n = 3 cluster of dimethyl ether shows sequential water loss, while all other ether clusters display selective product formation. The CID spectra are interpreted based on known energetics, and theoretical studies of the dimethyl and diethyl ether systems. Copyright © 2006 John Wiley & Sons, Ltd. [source] |