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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 2132-2139 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diastereoselectivity of the CC Bond Formation Reaction of Cyclic RadicalsSolvomercuration and reductive CC bond formation reaction of cyclopentene, dihydrofuran, cyclohexene, and dihydropyran with alkenes 4 yield products 9 - 16. In these reactions the formation of trans-isomers predominantes (Tables 1 - 3). The stereoselectivity increases with decreasing reactivity of alkenes 4 and is greater with five-membered than six-membered rings. Dihydrofuran reacts with methyl acrylate to give trans-and cis-Isomers 11f and 12f in a 93:7 ratio (Table 2). In contrast, norbornene yields only the exo, cis-isomer 21.
    Notes: Solvomercurierung und anschließende reduktive CC-Verknüpfung von Cyclopenten, Dihydrofuran, Cyclohexen und Dihydropyran mit Alkenen 4 liefern die Produkte 9 - 16, wobei die Bildung der trans-Isomeren überwiegt (Tab. 1 - 3). Die Stereoselektivität steigt mit abnehmender Reaktivität der Alkene 4 sowie beim Übergang vom Sechsring zum Fünfring an. Aus Dihydrofuran und Acrylsäure-methylester entstehen die trans-und cis-Isomeren 11f und 12f im Verhältnis 93:7 (Tab. 2). Im Gegensatz dazu reagiert Norbornen ausschließlich zu dem exo, cis-Isomeren 21.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 749-762 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Biological materials, rich in hemicelluloses (birch and pine wood, wheat straw and rice hulls) were disintegrated batchwise in a flow reactor with pure water at elevated temperatures and pressures. The resulting extractives and residual fibre compounds were characterized. Because of rapid removal of carbohydrate based extractives from the hot reaction zone, the degradation of pentosans and hexosans to furfural and hydroxymethylfurfural could be limited to only a small amount. Contrary to normal prehydrolysis conditions employing a sealed batch reactor, temperatures of 190 to 210°C and residence times of goods of 60 min are the optimum. Thus, hemicelluloses are dissolved and isolated with up to more than 90% yield. At temperatures above 225°C severe destruction of hemicelluloses and solvolysis of cellulose starts. Depending on disintegration temperatures, pentosan average molecular weights (M̄w) vary in case of birch wood between 3800 at 150°C and 900 at 225°C. The content of monomers rises with temperature and reaches a maximum of 45% at 225°C. DPw of residual cellulose is also temperature dependent and varies in case of birch wood and wheat straw between 1500 and 450. Lignin, which is mostly not dissolved, can be removed almost quantitatively by further treatment of the residue with ethanol/water at 250°C, thus allowing the isolation of relatively pure cellulose.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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