Chapter 24.6, Problem 38CC

Interpretation Introduction

Interpretation:

The epimers formed in successive Wohl degradation followed by Kiliani-Fischer synthesis for D-glucose should be determined.

Concept introduction:

• Aldohexose produce Aldopentose through Wohl degradation (chain shortening process).
• The Wohl degradation: aldoses is reaction with hydroxylamine and sodium methoxide which yields oxime then resultant oxime is reaction with acetic anhydride in acetic acid with sodium acetate which afforded chain shortened nitrile. In this reaction step the oxime is converted into the nitrile with simultaneous conversion of all the alcohol groups to acetate groups. Finally, sodium methoxide in methanol is added to the reaction which yields the final degradation compound.
• Aldopentose produces two aldohexoses through Kiliani-Fischer synthesis (chain lengthening process).
• In Kiliani-Fischer synthesis, sugar reacts with aqueous cyanide (NaCN); the cyanide undergoes nucleophilic addition to the carbonyl group of the sugar which yields cynohydrine. The resulting cyanohydrin is heated with water, which undergoes hydrolysis and forms carboxylic acid. These carboxylic acids react itself and form more stable lactones. Further, lactone is undergoes reduction reaction with a sodium amalgam which yields two aldohexoses.