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Monosaccharides
Concepts tested here
- Reducing nature of fructose
All Questions
2010 AIPMT-MAINS 1 question
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Fructose reduces Tollen's reagent due toFructose is a ketohexose; a keto group by itself is not oxidised by mild oxidising agents such as Tollens' reagent.
Tollens' reagent, however, is alkaline. In the presence of a base, fructose undergoes enolisation to form an enediol.
The enediol rearranges to give the aldoses glucose and mannose (Lobry de Bruyn–van Ekenstein rearrangement), so an equilibrium mixture containing a free –CHO group is formed.
The aldehyde group so produced reduces Tollens' reagent to metallic silver.
Hence fructose reduces Tollens' reagent because of enolisation followed by conversion to aldehyde by the base.