Monosaccharide Oxidation

Carbohydrates

Turning an aldose into aldonic acid

Differing attacks on aldoses/ketoses

Monosacharide Oxidation

• Sugar-COH -(Y)-> Sugar-COOH
  • Jones - CrO3 aq H2SO4/Acetone
  • Bromine Water - Br2/H2O
  • Nitric Acid - HNO3 Nitric Acid and Carbohydrates
  • Tollens - Ag/(NH3)2+ OH-
    • Basic conditions, consider Alpha Epimerization and Enediol Rearrangement
      • Alpha Epimerization = a condiseration of Epimers

Mechanism:

• Typical carbonyl attack
  • Displacing proton for OH

Differentiation of Reactions

• Bromine water only attacks carbonyl = ONE COOH
  • attacks aldoses
• HNO3 oxidizes both carbonyl and alcohol = TWO COOH
  • attacks aldoses
• Tollens only attacks carbonyl = ONE CARBOXYLATE
  • attacks either ketoses and aldoses
• Tollens creates an oxidized caboxylate ions and metalic silver
  • Strongly basic - Enediol and Alpha Epimerization
  • Indicator of reducing sugar

Fundamentals:

• Oxidizes aldoses not ketoses
• Cyclic form cannot open to the free chain carbonyl
• Acetals are stable under neutral and basic conditions
  • Cyclic acetals cannot open to the free carbonyl compound

Salient Examples:

Concepts:

• Jones Oxidation
• Redox Chemistry
• Carbonyl Chemistry

Terminology:

• Aldonic acid: sugar acids (gluconic acid) - only ONE COOH formed from the initial C1
• Aldaric acid: sugar acids (glucaric acid) - TWO COOHs formed from the initial C2 and the terminal carbon
• Epimers: sugars that differ only by the stereochemistry at the single carbon

Additional Information: