HYDROGENOLYSIS OF CARBOHYDRATES: VIII. COMPARATIVE STUDIES ON METHYL GLYCOPYRANOSIDES

Abstract

Several methyl glycopyranosides have been hydrogenated under pressure at 180 °C with copper chromite catalyst in dioxane. Many glycosides underwent hydroxyl group inversion and another reaction observed consisted of hydrogenolytic removal of the methoxyl group coupled with reduction of a hydroxyl group to a methylene group. Other glycosides were stable under these conditions, and these included methyl β- and methyl α-D-glucopyranosides and unexpectedly methyl β-D-mannopyranoside and methyl α-D-talopyranoside. The data indicated that generally β-glycosides are more stable than their α-anomers in the hexopyranoside series and that the methyl hexopyranosides are more stable than the methyl pentopyranosides. Explanations have been made in the theoretical section in order to cover these observations. At 240 °C, however, methyl α-D-glucopyranoside is hydrogenolyzed giving 11% of 1,5-anhydro-4-deoxy-hexitols. These polyols have been fractionated and the mixture shown to contain lyxo- and arabo-1,5-anhydro-4-deoxy-D-hexitols.