ISSN:
0449-296X
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Polymerization 1,6-anhydro-2,3,4-tri-O-benzyl-β-D-mannopyranose at -60°C with phosphorus pentafluoride (0.9 mole-%) gives stereoregular 2,3,4-tri-O-benzyl-[1 → 6]-α-D-mannopyranan with substantially higher viscosity ([η] = 2.8 dl/g) than the corresponding gluco- and glactopyranan derivatives prepared similarly. Debenzylation with sodium in liquid ammonia produces stereoregular [1 → 6]-α-D-mannopyranan of viscosity up to [η] = 0.54 dl/g. Stereoregular 2,3,4-tri-O-acetyl-[1 → 6]-α-D-glycopyranans are most simply prepared by acetylation of the corresponding crude [1 → 6]-α-D-glycopyranans obtained directly from the debenzylation reaction. The galactan is extremely difficult to acetylate by conventional methods if isolated in a pure form. Physical and spectral properties of these highly stereoregular synthetic 2,3,4-tri-O-acetyl-[1 → 6]-α-D-glycopyranans are presented. Optical rotary dispersion curves of 2,3,4, tri-O-acetyl-[1 → 6]-α-D-glycopyranans show small Cotton effects in the 200-230 nm region, superimposed on strong background rotation. Circular dichroism spectra show a single n →* acetate absorption band for each polymer. The sign of the band appears to be determined largely by the C-2 configuration. Stereoregular 2,3,4-tri-O-acetyl-[1 → 6]-α-D-glycopyranans in 2,2,2-trifluoroethanol solution are likely to possess a random rather than helical conformation.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1972.150100715
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