Glucose free gluconic acid

A reaction of practical importance is the oxidation of a carbohydrate aldehyde group to a carboxyl group. This is the basis for a process converting glucose to calcium gluconate, a substance of pharmaceutical interest. The oxidation reaction occurs at graphite electrodes in the presence of the Brj/Br" redox system. Calcium salt is added to the solution to prevent further oxidation of free gluconic acid. 

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... 

The situation was not so simple since similar results, conversion and selectivity, were obtained when comparing Ti-Y with the TiC>2-P25 catalyst from Degussa. Again, Ti-free materials were also found to be active. ZSM-5, Mordenite and L zeolites were shown to have nearly comparable glucose conversions (around 30%) and gluconic acid selectivity (around 20%), whereas Y and MCM-41 zeolites were found to be less active, but more selective, particularly in the case of Y (27%). Although the activity of the Ti-free Y catalyst is lower than that of the Ti-Y catalyst, a similar selectivity in gluconic acid is obtained for both catalytic materials, but the selectivity in other acids is less over the Ti-Y catalyst. 

With glucose, chemical oxidation of C-l occurs with the open-chain form, whereas enzyme-catalyzed oxidation of C-l occurs with the ring form of the sugar. The aldonic acid (gluconic acid) that is formed is an equilibrium mixture of the free acid (open chain) and the 5-lactone (ring). 

Fig. 2 -23. Oxidation of D-glucose (1) to D-gluconic acid (2) and o-glucaric acid (3). The free acids occur mainly as corresponding lactones.

Oxidation free carbonyl groups are able to reduce alkaline solutions of metal (mainly copper) salts to the free metal or to the oxide, to give aldonic acids. Thus glucose gives rise to gluconic acid (Fig. 7.6). When the hydroxyl group... 

Problem 35.2 The position of the free —OH group in 2,3,4,6-tetra-O-methyl-D-glucose was shown by tpc products of oxidative cleavage, as described in Sep. 34ASl What products would be expected from oxidative cleavage of 2,3,5,6-tetra-O-meihyl-D-gluconic acid ... 

Several alternative methods have been developed to retard this browning reaction. The most prevalent method is to reduce free glucose by a controlled bacteria or yeast fermentation to gluconic acid. The fermentation takes anywhere from 2 to 72 hours and adds considerable expense. With UF, protein concentration and glucose reduction can be accomplished simultaneously. 

D-Glucose Oxidases.—D-Glucose oxidase, in combination with glucoamylase and D-gluconolactonase, has been used to convert maltose into D-gluconic acid. A study has been made of the efficiency of a o-glucose oxidase-catalase system, both with the free and immobilized enzymes. ... 

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