Shortening the Carbon Chain of Sugars

Methods for Shortening the Carbon Chain of Sugars a. The Ruff Degradation 

One of the most useful methods for shortening the carbon chain of a sugar involves oxidation of a soluble salt of the aldonic acid with hydrogen peroxide in the presence of ferric acetate 184), Prior to the development of this method by Ruff, H. J. H. Fenton had shown that tartaric acid is oxidized by hydrogen peroxide in the presence of ferrous salts, but apparently no oxidative cleavage of carbon-carbon bonds was noted. The ferrous ion-catalyzed oxidation was extended to many carbohydrates by associates of Fenton (Chapter VI) and by other workers 185), The ferric ions used as the catalyst in the Ruff method permit the oxidation of aldonic acids but are inactive with respect to sugars. Ferrous ions are much less selective. 

Ruff applied the reaction to the easily available salts of the aldonic acids and showed that the oxidation takes place by the cleavage of carbon-carbon bonds and the direct formation of sugars. The yields are modest, but the sugars usually crystallize readily. n-Arabinose is produced from calcium D-gluconate in 50% of the theoretical quantity. The use of ion-exchange resins to remove ionic materials from the reaction mixture prior to isolation of the sugar is beneficial. By this technique, the yield of D-lyxose from calcium D-galactonate is increased from 17 to 41 % 186), Salts other than the 

The degradation procedure devised by Wohl 188) is essentially the reverse of the cyanohydrin synthesis. It involves the removal of the cyanide group from the acetylated nitriles, which in turn are formed from the oximes by application of the usual acetylation procedures. In the original process, the cyanide group was eliminated by the action of ammoniacal silver oxide. Under these conditions, the diacetamide compound of the low-er sugar results, and the free sugar is obtained from it by acid hydrolysis. 

Since acetamide, which results from ammonolysis of the ester functions, does not itself condense with free sugars 189) or acetylated aldehydo-sugars 190) the mechanism of formation of the diacetamide derivatives has received considerable study. A possible mechanism 191) is based on intramolecular migration of acetyl groups from oxygen to nitrogen, according to the scheme  

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Of the methods available for shortening the carbon chain of sugars, the Ruff degradation is generally one of the most facile. A soluble salt of a chosen aldonic acid is treated with hydrogen peroxide in the presence of... 

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