LOCATION OF O-ACETYL GROUPS IN THE ACIDIC D-XYLAN OF Mimosa scabrella (bracatinga). A STUDY OF O-ACETYL GROUP MIGRATION

Article abstract of DOI:10.1016/0008-6215(84)85010-7

Extraction with dimethyl sulfoxide of wood-meal of the stem of bracatinga (Mimosa scabrella), a south Brazilian hardwood, that was defatted and delignified by treatment with aqueous chlorine at 0 - 5 deg C followed by extraction with cold ethanol, gave a soluble O-acetylated 4-O-methyl-D-glucurono-D-xylan having (1 -> 4)-linked β-D-xylopyranosyl residues that were unsubstituted (65percent) and 2-O- (14percent), 3-O- (16percent), and 2,3-di-O-acetylated (5percent), as determined by methylation analysis.Another preparation obtained by use of refluxing ethanol in the delignification process showed neither removal nor migration of acetyl groups.By comparison with synthetic, partly O-acetylated D-xylans of known composition, 13C-n.m.r. spectroscopy indicated that O-acetyl group migration does not occur during treatment with cold aqueous chlorine, refluxing ethanol, or water at 70 deg C.Methyl 2-O-acetyl-4-O-methyl-β-D-xylopyranoside (6) was also unaffected by aqueous chlorine.O-Acetyl group migration took place more readily in aqueous and dimethyl sulfoxide solutions of 6 than of O-acetyl-D-xylans.The lowest temperatures at which migration was observed in monosaccharides was at 50 and 70 deg C for solutions in D2O and (CD3)2SO, respectively.