Answer to Question #20272 in Organic Chemistry for Richmond Marfo

Question

I read on the internet that ketoses are resistant to oxidation reactions and so does not react with Tollen's reagent. With Benedict's reagent however, ketoses can be converted to aldoses through the enediol intermediate.If this can happen then why does the same principle not happen with reaction with Tollen's reagent. Also what causes the conversion when reacted with Benedict's reagent.

Answer 1

Benedict's reagent (also called Benedict's solution ) is a chemical reagentnamed after an American chemist, Stanley Rossiter Benedict.
Benedict's reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and many disaccharides, including lactose and maltose . Even more generally, Benedict's test will detect the presence of aldehydes , and alpha-hydroxy-ketones, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent.