Reducing Powers of Various Sugars with Alkaline Copper.citrate Reagent

Scales' method for the determination of reducing sugars was modified by increasing the boiling time, and reducing values of 32 sugars were determined at various concentrations. The method as modified provides a very simple, convenient means for the quantitative determination of the various sugars. A comparison of the reducing values of different sugars reveals that the configurations of carbons 3, 4, and 5 have marked effect on the reducing values, but that the configuration of carbon 2 has little influence. Sugars in which the hydroxyl on carbon 3 is trans to the hydroxyls on carbons 4 and 5 have the highest reducing powers, while those which have cis hydroxyls on carbons 3 and 4 have lower reducing values. When the glycosidic union of a disaccharide is on carbon 3, the molecular reducing power is less than that of the monosaccharide corresponding to the reducing part of the molecule; if the glycosidic union is on carbon 4, the molecular reducing power is about 1.4 that of the corresponding monosaccharide, and if on carbon 6, the molecular reducing power is about 1.2 that of the corresponding monosaccharide. The effect of barium bromide on the reducing powers of the sugars varies with the experimental conditions. Under the conditions used in this investigation the presence of 6.5 percent of barium bromide lowers the reducing value by approximately 4 percent.