Oxidation to Aldonic, Dicarboxylic and Uronic Acids

Under mild conditions, e. g., with bromine water in buffered neutral or alkaline media, aldoses are oxidized to aldonic acids. Oxidation involves the lactol group exclusively. 3-Pyranose is oxidized more rapidly than the a-form. Since the P-form is more acidic (cf. 4.2.1.3), it can be considered that the pyranose anion is the reactive form. The oxidation product is the 5-lactone which is in equilibrium with the y-lactone and the free form of aldonic acid. The latter form prevails at pH 3. 

The dicarboxylic acid can, depending on its configuration, form mono- or dilactones. 

The transition of lactones from 5- to y-form and vice versa probably proceeds through an intermediary bicyclic form. 

The acid name is obtained by adding the suffix-onic acid (e. g. aldose aldonic acid). Glucono-5-lactone is utilized in food when a slow acid release is required, as in baking powders, raw fermented sausages or dairy products. 

An additional possibihty for uronic acid synthesis is the reduction of monolactones of the corresponding aldaric acids  

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