Oxidation of Monosaccharides. Monosaccharides are reducing sugars if their carbonyl groups oxidize to give carboxylic acids. In the Benedict’s text, D-glucose is oxidized to D-gluconic acid. Glucose is a reducing sugar. The chemistry of Benedict’s test.
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D-gluconic acid. Glucose is a reducing sugar.
Reducing sugars, those that contain a free aldehyde group, are oxidized by Cu2+which is reduced to Cu1+ and precipitates in a form of a red Cu2O.
Benedict’s reagent is an alkaline solution of CuSO4, Na2CO3, and sodium citrate (Na3C6H5O7∙2H2O). Sodium citrate forms a soluble complex with Cu2+ and prevents it from precipitating out as blue Cu(OH)2 or black CuO.
Loss of electrons
Gain of O
Loss of H (H+ & e)
Increase of the oxidation number (state)
Gain of electrons
Loss of O
Gain of H (H+ & e)
Decrease of the oxidation number (state)
Mg0 → Mg2+ + 2 e│2
O20 + 4 e → 2 O2-
Ag+ + e → Ag
NO3- + 2H+ + 2e → NO2- + H2O
2 CO2 + 2H+ + 2e → H2C2O4