Oxygen in Alkaline or Neutral Solution

The study of the action of molecular oxygen on sugars is of considerable interest from the standpoint of the mechanism of the in vivo oxidations of 

3-(a-D-Glucopyranosyl)-D-arabonic acid is obtained from maltose, and the jS-isomer from cellobiose 24 ). 3-(jS-D-Galactopyranosyl)-D-arabonic acid is formed similarly from lactose. A quantitative experiment on the effect of oxygen on glucose in aqueous potassium hydroxide shows the main products to be D-arabonic acid and formic acid, with lactic, oxalic, and carbonic acids formed in minor amounts 243), 

In neutral solution in the presence of platinum catalyst, the process is mainly one of dehydrogenation, and the oxidation of mannose is postulated 244) as follows  

D-Mannose — D-mannonic acid — L-mannuronic acid mannaric acid 

The platinum oxide catalyst converts the hexitols to the corresponding aldoses and ketoses which are carried through the above series of reactions by the oxygen. Mannitol is oxidized by Pt02 to D-mannose, isolated as methyl a-mannoside in a yield of 20%. Fructose is formed simultaneously. With a platinum-activated carbon catalyst, L-sorbose has been converted to 2-keto-L-gulonic acid, 2,3-0-isopropylidene-L-sorbose to2,3-0-isopropyl- 

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