Chain Shortening The Ruff Degradation

There are a number of ways in which an aldose can be converted into another aldose of one less carbon atom. One of these methods for shortening the carbon chain is the Ruff degradation. An aldose is oxidized by bromine water to the aldonic acid oxidation of the calcium salt of this acid by hydrogen peroxide in the presence of ferric salts yields carbonate ion and an aldose of one less carbon atom (see Fig. 34.3). 

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... 

The Ruff degradation is the opposite of the Kiliani-Fischer synthesis. Thus, the Ruff degradation shortens an aldose chain by one carbon Hexoses are converted into pentoses, and pentoses are converted into tetroses. In the Ruff degradation, the calcium salt of an aldonic acid is oxidized with hydrogen peroxide. Ferric ion catalyzes the oxidation reaction, which cleaves the bond between C-1 and C-2, forming CO2 and an aldehyde. It is known that the reaction involves the formation of radicals, but the precise mechanism is not well understood. 

Just as the Kiliani—Fischer synthesis can be used to lengthen the chain of an aldose by one carbon atom, the Ruff degradation can be used to shorten the chain by a similar unit. The Ruff degradation involves (1) oxidation of the aldose to an aldonic acid using bromine water and (2) oxidative decarboxylation of the aldonic acid to the next lower aldose using hydrogen peroxide and ferric sulfate. d-(—)-Ribose, for example, can be degraded to D-(—)-erythrose ... 

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

Nature forms, stores, and uses chemical energy. Carbohydrates are the central chemical in this dance of life. Chemists manipulate saccharides many ways, as well. The Kdiani-Fischer synthesis lengthens a carbohydrate chain by one carbon atom. The Ruff degradation shortens the chain by one carbon. Both reactions occur without disturbing the remaining stereogenic carbons. 

Methods have been developed both to lengthen the carbon chain in a carbohydrate (Kiliani—Fischer synthesis) and to shorten it (Ruff degradation). 

Chain shortening. In the Ruff degradation, the original aldehyde group is lost and a new aldehyde created at the old C(2) (Fig. 22.21). 

The sugar chain can be lengthened (Killani-Fischer reaction) or shortened (Wohl or Ruff degradations. 

Ruff-Fenton degradation. Shortening of the carbon chain of sugars by the oxidation of aldonic acids (as calcium salts) with hydrogen peroxide and ferric salts. 

---