Galactose Wohl degradation

Conversion of the aldehyde into a nitrile is accomplished by treatment of an aldose with hydroxvlamine to give an oxime (Section 19.8), followed by dehydration of the oxJme with acetic anhydride. The Wohl degradation does not give particularly high yields of chain-shortened aldoses, but the reaction is general for all aldopentoses and aldohexoses. For example, D-galactose is converted by Wohl degradation into n-lyxose. 

D-Galactose. Wohl and List prepared pentaacetyl-n-galactononitrile from the oxime in 40% yield. Degradation with ammonia-silver oxide gave 40% of n-lyxose diacetamide. Hydrolysis of the diacetamide with... 

The Wohl degradation converts a stereogenic center at C2 in the original aldose to an sp hybridized C=0. As a result, a pair of aldoses that are epimeric at C2, such as D-galactose and D-talose, yield the same aldose (D-lyxose, in this case) upon Wohl degradation. 

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