Monosaccharides Ruff degradation

Problem 22.24 What monosaccharide is obtained from a Ruff degradation of o-mannose (Problem 22 11), the C epimer of o-glucose (Problem 22.23)7 ... 

Reduction of an aldose forms one alditol reduction of a ketose forms two alditols. Br2 oxidizes aldoses, but not ketoses ToUens reagent oxidizes both. Aldoses are oxidized to aldonic acids or aldaric acids. Aldoses and ketoses react with three equivalents of phenyUiydrazine, forming osazones. C-2 epimers form identical osazones. The Kiliani-Fischer synthesis increases the carbon chain of an aldose by one carbon— it forms C-2 epimers. The Ruff degradation decreases the carbon chain by one carbon. The OH groups of monosaccharides react with acetyl chloride to form esters and with methyl iodide/silver oxide to form ethers. 

A D-aldopentose is oxidized by nitric acid to an optically active aldaric acid. A Ruff degradation of the aldopentose leads to a monosaccharide that is oxidized by nitric acid to an optically inactive aldaric acid. Identify the D-aldopentose. 

The Ruff degradation and the Wohl degradation both cleave the carbonyl-bearing carbon from a monosaccharide to form a new monosaccharide of one fewer carbon. The Nef reaction adds one carbon to a monosaccharide to form a new monosaccharide, as does the Fischer-Kiliani synthesis. 

Ruff degradation gives low yields because of the sensitivity of the products to the reaction conditions. Nevertheless, the procedure is useful in structural elucidations (Exercise 24-25). Fischer originally carried out such studies to establish the relative configurations of the monosaccharides (the Fischer proof). The next section will describe some of the logic behind his approach to the problem. 

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