Platinum gluconic acid oxidation

As with platinum, the palladium-catalyzed oxidation of anomeric hydroxyl groups in aldoses is a rather selective process.84 The influence of pH in the Pd-catalyzed oxidation of glucose has been studied. It was observed that the gluconic acid formed, in its free form, reversibly inhibits the oxidation process in acidic media.85 The oxidation of D-glucose has been performed with palladium-on-alumina and with bismuth-containing palladium-on-charcoal in water.85 The selectivity in the air oxidation of... 

Glucose can be oxidized to gluconic acid by oxygen (4.38) in the presence of palladium on alumina, a palladium-bismuth catalyst, or a platinum-bismuth catalyst in 99-100% yield.186... 

The oxidation of D-glucose to D-gluconic acid is also readily carried out by use of a platinum-on-carbon catalyst (a substantially more-active catalyst) in the presence of an equivalent of alkali. With the aid of the same catalysts, n-galactose, D-mannose, D-xylose, and L-arabinose can be converted to the corresponding aldonic acids. By this method, the pentoses are oxidized more rapidly than the hexoses. A reaction time of only 45 minutes is required at 22°, whereas the oxidation of D-glucose is complete only after five hours. 

Glucose oxidase is immobilized in a polyacrylamide matrix. Oxygen and quinone which serve as mediators are reduced to hydrogen peroxide and hydroquinone, respectively. Since their oxidation starts at E, > 0.7-0.9 V, it is possible to displace the initial potential for the oxidation of glucose by 0.6-0.8 V towards positive values compared to its stationary electrochemical oxidation to gluconic acid on platinum. ... 

The formation of D-glucaric acid by platinum-catalysed oxidation of D-gluconic acid has been noted in the previous section. Mono- and per-allyl ether derivatives of xylaric and galactaric acids have been prepared by treating the aldaric acid with allyl alcohol in the presence of an appropriate acid catalyst. Diallyl 3-0-allyl-2,4-0-methylenexylarate was obtained in good yield when 2,4-0-methylenexylaric acid reacted with allyl bromide in the presence of alkali. The reaction of 2,3,4-tri-O-acetylxylaryl dichloride with diazomethane has been mentioned in Chapter 7. 

A variation of the bromine oxidation process which seems to be particularly feasible for the commercial production of aldonic acids involves the electrolysis between carbon electrodes of solutions containing sugars, small amounts of bromides, and a buffer such as calcium carbonate 179), Presumably the reaction takes place by the formation of free bromine at the anode the bromine oxidizes the aldose to the aldonic acid and is reduced to bromide. Yields are almost theoretical in many cases. If the electrolytic method is not well controlled, saccharic acids and 2-keto and 5-keto aldonic acids may be produced 180), Whereas the normal electrolytic oxidation is conducted with direct current, a yield of 55 % of gluconic acid has been obtained with alternating current 181) and platinum electrodes a very low efficiency was observed with graphite electrodes. 

Colloidal Au and Au/C catalysts can be used to oxidize d-glucose to d-gluconic acid [1,77], In fact, Au/C catalyst is a valid alternative to most of the investigated multimetallic catalysts based on palladium or platinum. Moreover, gold has the unique property of operating without the external control of pH, thus ensuring total conversion at all pH values and total selectivity to gluconic... 

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