Transformations of sugars in alkaline solutions

Oxidation of Pentoses in Alkaline Solution

“…It can be seen that the relative rate of disappearance of the pentoses agrees well with their relative rates of oxygen uptake; however, the relative reactivities of the pentoses was at first surprising because it differed significantly from the relative rates of enolization reported by Isbell and co-workers (15) (15) found that ketoses, such as fructose, take up tritium faster than aldoses, and they suggested that this may be due to the reversible formation from the ketoses of glyceraldehyde and its enediol, to the presence of three replaceable hydrogens a to the carbonyl group, and to the possibility of a p-elimination reaction leading to an unsaturated sugar that can rearrange with hydrogen incorporation. Since a pentose could be converted to a ketose the figures given for tritium uptake of the pentoses may not reflect the primary rate of enolization alone.…”

Carbohydrates in alkaline systems. I. Kinetics of the transformation and degradation of D-glucose, D-fructose, and D-mannose in 1 M sodium hydroxide at 22 °C

“…Isbell et al (29) have also pointed out the higher rate of enolization of 2-deoxy-sugars (90-155 compared to 1.0 for glucose) and ascribed this to the higher proportions of acyclic intermediates. Penta-0-methyl-aldehydo-D-glucose, containing a free carbonyl group, is extremely reactive to alkali ; Anet (30) found that it was readily rapidly converted by 0.02 N lime water into an unsaturated derivative.…”

“…They also studied the enolization (uptake of tritium in 0.5 M sodium carbonate in water-t) at 25" (29). The rate was very low; after 28 h the reaction for glucose was only 1.39 % complete.…”

Carbohydrates in alkaline systems. II. Kinetics of the transformation and degradation reactions of cellobiose, cellobiulose, and 4-O-β-D-glucopyranosyl-D-mannose in 1 M sodium hydroxide at 22 °C

“…While this work was confined mostly to monosaccharides, they did determine the rate of enolization (uptake of tritium in 0.5 M sodium carbonate in water-t) at 25" for several disaccharides (12). The relative rate of enolization was 2.6, compared to 1.0 for glucose.…”