Uronic acids reducing action

Oxidation of an aldobiouronic acid with bromine under nonhydrolytic conditions produces a dibasic acid in which the new carboxyl is formed from the original hexose or pentose unit. This is shown by the fact that such an acid (when the reducing portion of the original biouronic acid is a hexose) will form the same amount of furfural as the original acid under the action of 12% HCl. Evidently, the glycosidic linkage is formed from the hemiacetal group of the uronic acid. Oxidation with bromine under hydrolytic conditions produces a dibasic and an aldonic acid and allows identification of the two units. 

Low yields of uronic acid usually result from the action of selective oxidants on glucosides and non-reducing acetals of the aldoses in which all the hydroxyl groups are free. However, a 56% yield of D-galacturonoside has been claimed for the oxidation of methyl a-D-galactopyranoside with nitrogen dioxide . 

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