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991.
Frank Mallwitz Werner A. Goedel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2001,113(14):2625-2625
992.
Silylation of cellulose with hexamethyldisilazane (HMDS) in liquid ammonia is described emphasizing mechanistic features. Conditions for complete as well as for stoichiometric partial silylation have been established which proved that the ratio of silylating agent and hydrogen bonding capability of the solvent are crucial for complete silylation. The heterogeneous reaction follows first order kinetics in the presence of saccharine as catalyst indicating that the accessability of hydroxy groups is not the rate determining factor. Stoichiometric desilylation of trimethylsilyl cellulose is also possible in tetrahydrofurane containing ammonia as hydrogen bond donor. Trimethylsilyl celluloses have a solubility window in THF with a DS from 1.6 to 2.6 which is narrower for higher molecular weight of the cellulose. Trimethylsilyl celluloses with DS above 2.7 show thermotropic behaviour. 相似文献
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N. Tsevegsüren K. Aitzetmüller L. Brühl Gisela Werner 《Journal of separation science》2000,23(5):360-366
Seed oils from the Compositae plant family are known to contain a variety of unusual fatty acids. Subsequent to the recent discovery of γ‐linolenic acid in Saussurea and Youngia, further Mongolian Compositae species were investigated for their seed oil fatty acid composition. A number of δ3trans‐fatty acids (16 : 1δ3t, 18 : 1δ3t and 18 : 3δ3t, 9c, 12c) were found in the seed oils of Heteropappus hispidus and Asterothamnus centrali‐asiaticus. The latter fatty acid, but not the trans‐monoenes, was also found in one species of Artemisia. These unusual fatty acid isomers were characterized by capillary gas‐liquid chromatographic (GLC) separations in combination with other chromatographic techniques (analytical thin layer chromatography, TLC and preparative argentation TLC), and infrared spectrocsopy (IR). Their identity was further confirmed by co‐chromatography with other seed oils known to contain these trans‐fatty acids. The fact that within the Compositae plant family there are apparently two or three distinct groups of genera containing δ3trans‐fatty acids is discussed. 相似文献
995.
CuAl2F2(Si2O7) has been prepared by hydrothermal synthesis and its crystal structure was determined by single crystal X‐ray diffraction: space group Pnma, a = 8.8697(9), b = 14.084(2), c = 4.7553(5) Å, wR2 = 0.056, R = 0.022. Cu2+ shows elongated square pyramidal coordination. Edge‐ and corner‐sharing [AlO4F2] octahedra with fluorine atoms in cis position form layers parallel to the ac plane. Along b these layers are linked by Si2O7 groups to form a three‐dimensional framework [Al2F2(Si2O7]2–. In addition, the [CuO5] pyramides connect two Al octahedra of neighbouring layers. The crystal structure is discussed as a derivative from topaz structure. The modular (or polysomatic) approach is used for this purpose, and for modelling hypothetical related compounds. 相似文献
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