Understanding Fructose: The Role of Ketone in Reducing Sugar Reactions

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Discussion Overview

The discussion revolves around the chemical properties of fructose as a reducing sugar, specifically focusing on the role of its ketone group in oxidation-reduction reactions. Participants explore the mechanisms involved in these reactions, including the iodoform reaction and the oxidation of ketones.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant states that fructose is a reducing sugar and that its ketone group reduces Cu2+ to Cu+, resulting in the oxidation of fructose itself.
  • Another participant questions how a ketone group can be oxidized, noting that aldehydes oxidize to carboxylic acids while ketones do not.
  • A suggestion is made to look up the iodoform reaction, although its relevance to the discussion is questioned.
  • A participant recalls that the ketone may be reduced to a carboxylic acid, but expresses uncertainty about this claim and suggests finding the mechanism.
  • One participant mentions that fructose can isomerize to glucose and mannose through an enediol intermediate, which then undergoes oxidation in the Benedict's test.
  • Another participant briefly notes the possibility of oxidizing a ketone using carbonyl oxides.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the oxidation of ketones and the behavior of fructose as a reducing sugar. There is no consensus on the mechanisms or outcomes discussed.

Contextual Notes

Participants express uncertainty about the oxidation of ketones and the specific reactions involved, indicating a need for further exploration of the mechanisms and conditions under which these reactions occur.

garytse86
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Fructose is a reducing sugar, and the ketone acts as a reducing centre, which reduces Cu2+ --> Cu+. Therefore fructose itself becomes oxidised.

However, how can a ketone group be oxidised?

I thought: aldehyde becomes oxidised to carboxylic acid
ketone: cannot be oxidised.
 
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Try looking up the iodoform reaction.
 
How does that help. I know the iodoform reaction confirms any 2-one, 2-ol, 2-al, ethanol or ethanal. i.e. CH3C=O, but no hydroxide / iodine for reducing sugar test?
 
Well, from what I remember, the ketone is reduced in this case to a carboxlic acid, although not completely sure. Try finding the mechanism, I just don't have the time right now.
 
Yeah, the fructose isomerizes to glucose and mannose via an enediol, which then oxidizes in the standard Benedict's test fashion.

My students happen to be doing that very experiment today.

If you want to oxidize an actual ketone, there's always carbonyl oxides...
 
ok, thank you very much :D
 

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