Glycosidation of Sugars: I. Formation of Methyl- D -Xylosides

The reactions of D-xylose, methyl α-D-xylofuranoside, and methyl β-D-xylopyranoside with methanolic hydrogen chloride under controlled conditions have been followed by gas–liquid partition chromatographic analysis of the products. Rate curves were established for each of the four methyl-D-xylosides and the results showed that the following sequence of reactions occurs in the formation of methyl xylosides: (1) xylose → furanosides, (2) anomerization of furanosides, (3) furanosides → pyranosides, (4) anomerization of pyranosides. The relative rates of these four reactions in order of decreasing velocity are 2, 1, 3, 4. Reaction 3 appears to proceed with retention of configuration at the anomeric center. Possible intermediates in these reactions are discussed. Substitution of positions 2 and 3 in the D-xylose molecule by O-methyl groups resulted in an increase in the furanoside content of the methanolysis products at equilibrium.