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Question

Write short notes on reducing and non-reducing sugars.


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Solution

Reducing Sugar

  • Reducing sugar is one that possesses a free aldehyde or ketonic group.
  • It can reduce Fehling and Tollens reagent.
  • Fehling A is Copper sulfate CuSO4and Fehling B is an aqueous solution of potassium sodium tartrate KNaC4H4O6·4H2O.
  • Tollens's reagent is the ammoniacal solution of silver nitrate ([Ag(NH3)2]+)
  • Reducing sugar can act as a reducing agent.
  • It can be further reduced to alcohol.
  • For example maltose and lactose.

Non reducing sugar

  • In a basic aqueous solution, a non-reducing sugar is not reduced by a weak oxidising agent (one that oxidises aldehydes but not alcohols, such as Tollen's reagent).
  • There is no free aldehyde or ketonic group.
  • Non-reducing sugars do not have an -OH group attached to the anomeric carbon so they cannot reduce other compounds.
  • E.g. sucrose and Raffinose
  • The structure of sucrose is as follows:-


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