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Fructose reduces Tollen's reagent due to
A
Asymmetric carbons
B
Primary alcoholic group
C
Secondary alcoholic group
D
Enolisation of fructose followed by conversion to aldehyde by base
Detailed Solution
Fructose 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.
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.