Question

Even though sucrose is considered a non-reducing sugar, it may have acted as a reducing sugar with certain reagents. Suggest a reason for this observation.

Answer 1

A reducing sugar is any sugar that either has an aldehyde or keto group or is capable of forming one in solution through isomerism. Sucrose is a disaccharide combination of the monosaccharides glucose and fructose through anomeric carbon.

The reducing ability of disaccharides is defined by the presence of a potential aldehyde or ketone group.

sucrose's anomeric carbon is not "free" since this carbon is used to link fructose and glucose together. therefore, the anomeric carbon can't open up the ring structure to form the aldehyde.

However, when sucrose can indirectly produces a positive result with Benedict's reagent if heated with dilute hydrochloric acid prior to the test, although after this treatment it is no longer sucrose. The acidic conditions and heat break the glycosidic bond in sucrose through hydrolysis. The products of sucrose decomposition are glucose and fructose, both of which can be detected by Benedict's reagent.