Preparation of Products other than Aldonic Acids

Tiemann studied the further oxidation of D-gluconic acid with bromine at 100 a reducing sirup was formed which was isolated as an amorphous barium salt or a crystalline osazone. Ruff repeated the work and could find no oxygluconic acid in the oxidation mixture most of the D-gluconic acid was unaltered and the reducing power was very low, especially in comparison with that obtained when keto aldonic acids were prepared by the action of hydrogen peroxide and ferrous salts. By ether extraction and distillation the formation of formic, oxalic and glycolic acids was shown. 

The oxidation products of L-rhamnose treated with an excess of bromine for five days included a small amount of 5-keto-L-rhamnonic lactone 1000 g. of L-rhamnose gave 550 g. of L-rhamnonic lactone and 55 g. of the keto derivative. In confirmation, Voto6ek and Malachata achieved the partial conversion of L-rhamnonic lactone to the keto derivative. The very low yield, however, is indicative of the slowness of the reaction and the relative stability of the normal aldonic acids or lactones toward further oxidation. 

Everett and coworkers have done extensive work on this overoxidation of aldoses with bromine at 25° for long periods of time (forty to fifty days). Under these conditions, appreciable amounts of the keto acids are obtained. Hart and Everett obtained 5-keto aldonic acids from D-glucose, D-mannose, D-galactose, D-xylose and D-gulonic lactone. The barium salts were isolated and converted to the brucine salts. The structure of the oxidation product from D-xylose was not determined. The stability of these keto acids to further bromine oxidation had been noted earlier by Kiliani.  

One very interesting case is that of L-rhamnose. Hart and Everett obtained not only the expected 5-keto-L-rhamnonic acid but also 5-keto-L-mannonic acid (5-keto-D-gulonic acid) this was the first reported instance in which a — CH3 group had been oxidized by bromine water to a — CHaOH group. The yields of the brucine salts of the two acids were 

from 4 g. of L-rhamnose. The identity of the 5-keto-L-mannonic acid was checked by the fact that it was also prepared by the oxidation of n-gulonic lactone. 

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Preparation of Products other than Aldonic Acids. 146... 

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