Gluconic platinum

Palladium is superior to platinum with respect to both activity and selectivity in this process. More recently, bi- (e.g. Pd, Bi/C)37 and trimetal lie (Pd, Pt, Bi/C)38 catalysts have been described that afford very high selectivities to gluconic acid. For example, Degussa workers38 obtained gluconic acid in 96% selectivity using a 4% Pd, 1% Pt, 5% Bi-on-charcoal catalyst at pH 10, 55°C and 10 mbar 02 pressure. Pt enhances the activity and Bi the selectivity of the Pd catalyst. 

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... 

Figure 21.16 shows the variations of the current intensity and the charge involved during the oxidation reaction of glucose on a platinum electrode. At the end of electrolysis, gluconate was... 

As shown in different works,41 65-71 the mechanism of glucose electrooxidation on platinum is similar to that on gold electrode. The primary and main reaction product remains 8-gluconolactone that is transformed into gluconate by hydrolysis. 

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. 

The facile dehydrogenation of o-glucose and related mono- and disaccharides such as D-galactose and lactose on platinum or rhodium catalysts under alkaline conditions (pH 13.5) has been reported [49]. During this reaction, hydrogen was evolved whereas o-glucose was transformed into o-gluconic acid. Other metals, e. g. nickel, palladium, and ruthenium, were less active and much less selective (Scheme 4). 

Unpromoted platinum catalysts selectively oxidize the primary alcohol function of D-gluconate 1 to yield D-glucarate 2 (see Section 9.3.3.2, Figure 5). Smits et al. 

In a similar investigation, Besson et al. [45] found that addition of bismuth to platinum had a similar effect. As in the previous investigation, however, the reaction was conducted at basic pH, and the yield of 2-keto-D-gluconate was limited by the formation of degradation products. 

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. ... 

Platinum catalysts supported on activated charcoal, with or without promoters such as bismuth or gold, have been examined for selectivity in the air oxidation of aqueous D-glucose and D-gluconate to glucarate. Palladium(II) has been found to inhibit the oxidation of aldoses by alkaline Fe(CN6) , and by Ce(IV). ... 

The rate and efficiency of crystallization of calcium gluconate from solution following the electrode oxidation of glucose have been investigated, and this reaction at a platinum electrode is markedly catalysed by submonolayers of heavy metals (e.g, thallium,... 

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