MODULE 2 - MONO AND DISACCHARIDE

• CARBOHYDRATES

  • general formula : Cn(H2O)n
  • Aldehydes and ketones w/ one or more –OH groups
  • Polyhydroxy aldehydes (aldoses)
  • Polyhydroxy ketones (ketoses)
• MONOSACCHARIDES

  • a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate
  • Monosaccharides have the general formula CnH2nOn, where n varies from 3 to 8
  • Aldose: a monosaccharide containing an aldehyde group.
  • Ketose: a monosaccharide containing a ketone group
• Molisch’s Test

  • General test for Carbohydrates
  • Reagent:  α-Naphthol, conc. sulfuric acid
  • Positive result: Formation of purple ring at the junction of the solution
• Schiff’s Test

  • General test for the presence of aldehydes functional group
  • Positive result: formation of purple/magenta product (shades may vary)
  • Reagent; Schiff’s reagent (para-rosanilin with sulfurous acid) 🡪 colorless or very pale yellow
• Oxidation of Monosaccharides  to Aldonic Acids

  • The aldehyde group of an aldose is oxidized under basic conditions to a carboxylate anion.
  • The oxidation product is called an aldonic acid.
  • A carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing sugar (it reduces the oxidizing agent).
• Oxidation Tests:

  • Tollen’s Test (Oxidation by Silver Ion)
  • Fehling’s Test (Oxidation by Copper Ion)
  • Benedict’s Test
  • Nylander’s Test
  • Moore’s Test
  • Picric acid Test
• Tollen’s Test (Oxidation by Silver Ion)

  • a.k.a. “Silver Mirror Test”
  • Determines the reducing property of sugars
  • Positive result; formation of silver mirror
  • Reagent: silver nitrate in ammonia water (or ammoniacal AgNO3) 🡪 oxidizing agent
• Equation of Tollen's Test:

  
• Fehling’s Test (Oxidation by Copper Ion)

  • Determines the reducing property of sugars
  • Positive result: formation of brick red ppt
  • •Reagent: equal volumes of: Fehling's Solution
  • Fehling’s B (potassium sodium tartrate tetrahydrate or Rochelle salt in NaOH solution)
  • Fehling’s A (hydrated CuSO4 solution)
• Equation for Fehling’s Test:

  
• Benedict’s Test

  • Determines the reducing property of sugars
  • Positive result: formation of brick red ppt.
  • Reagent:CuSO4, NaOH, sodium citrate
• Equation for Benedict's Test:

  
• Nylander’s Test

  • Determines the reducing property of sugars
  • Positive result: formation of black ppt.
  • Reagent: Bi(OH)2NO3 (Bismuth  subnitrate), KOH
• Equation of Nylander's Test

  
• Moore’s Test

  • Determines the reducing property of sugars
  • Positive result: golden brown solution
  • Reagent: strong NaOH
• Equation of Moore's Test:

  
• Picric Test

  • Determines the reducing property of sugars
  • Positive result: Mahogany Red solution
  • Reagent: picric acid solution and sodium carbonate
• Equation of Picric Test:

  
• Disaccharide - A disaccharide is a sugar formed by the condensation of two monosaccharides.

  
• RESULTS: