Search results for "ALK"
showing 10 items of 4314 documents
Bestimmung des vernetzungsgrades schwach vernetzter, noch löslicher copolymerer aus styrol und bisacrylsäurephenylestern durch hydrolytischen abbau
1970
Aus Styrol und Bisacrylsaurephenylester durch radikalische, vernetzende Polymerisation erhaltene und in Toluol sowie Dioxan noch losliche Copolymere wurden durch alkalische Hydrolyse gezielt in die linear strukturierten Bestandteile zerlegt. Diese enthielten neben sehr vielen Styrolbausteinen wenige aus dem Vernetzer stammende Acrylsaurebausteine. UV-Spektren zeigten, das die Vernetzerreste durch den hydrolytischen Abbau vollstandig abgespalten waren. Von den linearen Baustucken wurden viskosimetrisch, osmometrisch und z. T. colorimetrisch die Molekulargewichte bestimmt. Die Hydrolyseprodukte zeigten eine unerwartet bei 320 mμ auftretende Extinktion, deren Ursache nicht restlos aufgeklart w…
Ionic Liquids on Demand in Continuous Flow
2009
We report on the development of an alternative protocol for the facile, solvent-free synthesis of various novel imidazolium-based ionic liquids (ILs) that affords highly pure products without the necessity of subsequent purification steps. The continuous approach is based on the combination of HPLC pumps with a micromixer and a capillary residence tube. Our system provides a high degree of control over the alkylation reactions due to a high surface-to-volume ratio and superior heat and mass transport. Within the scope of our studies, we focused on ionic liquids containing differently substituted phenyl rings and characterized these compounds with respect to further use for direct applicatio…
Die Kationische ɛ-Caprolactam-Polymerisation. V. Die quantitative Bestimmung der N-Acyllactam-Gruppen bei der Initiierung mit wasserfreien Säuren und…
1971
Als Beitrag zur Aufklarung des Mechanismus der kationischen Caprolactam-Polymerisation mit wasserfreien Sauren (z. B. HCl) als Initiatoren wurde der Gehalt der C-terminal entstehenden N-Acyllactam-Endgruppen und anderer funktioneller Gruppen der gebildeten Oligo- und Polyamide quantitative bestimmt. Dies erfolgte auf IR-spektroskopischem Wege und durch potentiometrische Titration der nach alkalischer Hydrolyse gebildeten Carboxylgruppen. Fur die Polymerisation wurde ein verbessertes Verfahren ausgearbeitet, das vollstandigen Sauerstoff- und Feuchtigkeitsausschlus ermoglicht und damit besser reproduzierbare Ergebnisse liefert. Die Abhangigkeit der Konzentration verschiedener funktioneller Gr…
Reactions of 4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidines with α,β-unsaturated carbonyl compounds
2004
The reaction of 5,7-diphenyl-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine (1) with α,β-unsaturated carbonyl compounds 2a-f led to the formation of the alkylated heterocycles 3a-f (Figure 1). However, the reaction of 5-methyl-7-phenyl-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine (5) with 2a-c yielded under the same conditions the triazolo[5,1-b]quinazolines 6a-c (Figure 3). In this case, the alkylation is followed by a cyclocondensation. The structure elucidation of the products is based on ir, ms, 1H and 13C nmr measurements and on an X-ray diffraction study.
1,2-Asymmetric Induction in Diastereoselective Zwitterionic Aza-Claisen Rearrangements: Key Steps in Optically Active Alkaloid Synthesis
2013
The zwitterionic aza-Claisen rearrangement of optically active N-allylpyrrolidines and α-phenoxyacetyl fluorides proceeds with complete simple diastereoselectivity (internal asymmetric induction) and complete 1,2-asymmetric induction to generate a new C–C bond adjacent to a chiral C-N-Boc functionality. The resulting γ,δ-unsaturated amides were cyclised to give the corresponding pyrrolizidinones, which enabled the determination of the relative configuration of the stereotriads. Vinyl group degradation and a final lactam reduction gave an optically active analogue of (+)-petasinine (a pyrrolizidine alkaloid). Furthermore, the stereotriad-containing amides should be useful key intermediates f…
1990
The effect of lithium tert-butoxide (t-BuOLi) on rate constants and equilibrium constants of reactions involved in the initial stage of the anionic polymerization of methyl methacrylate (MMA) in tetrahydrofuran, initiated by methyl α-lithioisobutyrate (P) was investigated at 23 ± 3°C. Addition of t-BuOLi decreases the rate constants of initiation and propagation by one order of magnitude; the rate constants of termination by cyclization decrease by two orders of magnitude. This leads to an overall tenfold higher preference of propagation with respect to termination and explains the favourable effect of alkoxide in the polymerization reported earlier. Within experimental error, the equilibri…
Functionalization with silyl enol ethers, VI Zinc chloride mediated alkoxyalkylation of O-methyl-O-trimethylsilyl) keten acetals with 2-alkoxy-1,3-di…
1987
O-Methyl-O-(trimethylsilyl) keten acetals2 were regioselectively alkoxyalkylated by 2-alkoxy-1,3-dioxolanes1 in the presence of zinc chloride. This method represents a good way for synthesis of α-protected β-keto carbonic esters4.
Stereocontrolledα-Alkylation of Fully ProtectedL-Serine
2004
Diastereoselective alkylation of the (2S,4S) and (2R,4S) diastereomers of 3-tert-butyl 4-methyl 2-tert-butyl-1,3-oxazolidine-3,4-dicarboxylate (1a/b) is reported. Formation of both diastereomers of these oxazolidines was achieved by changing the order of protection steps, and their relative and absolute configurations were determined by NOESY spectroscopy. The use of the bulky ring substituent tBu together with Boc as the N-protecting group led to the exclusive formation of only one alkylated diastereomer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)