Glucose and Fructose: Concepts, Properties, and Applications

I. Glucose (C6H12O6)

1. Concept:

• Glucose is a type of monosaccharide, commonly known as grape sugar.
• It is the main component of many ripe fruits, honey, and is found in leaves, flowers, roots, and ripe fruits.
• It is present in human blood at a concentration of about 0.1%.
• In honey, glucose accounts for about 30%.

2. Structure:

• Open Chain: Glucose has an open chain structural formula of CH2OH-(CHOH)4-CHO.
• Ring Structure: Glucose mainly exists in a 6-membered ring form (pyranose) with two isomeric forms: α and β.
  • α-glucose: The -OH group at C1 is below the plane of the ring.
  • β-glucose: The -OH group at C1 is above the plane of the ring.

3. Properties:

• Aldehyde Properties:
  • Silver Mirror Reaction: Glucose reacts with AgNO3/NH3 solution to form a silver precipitate.
  • Oxidation Reaction: Glucose is oxidized by Br2/H2O to form gluconic acid.
• Properties of Polyhydric Alcohol:
  • Formation of Blue Complex with Cu(OH)2: 2C6H12O6 + Cu(OH)2 → (C6H11O6)2Cu + 2H2O.
• Reduction Reaction: Glucose is reduced by H2 to form sorbitol: C6H12O6 + H2 → C6H14O6 (Sorbitol).
• Alcoholic Fermentation: C6H12O6 → 2C2H5OH + 2CO2.

4. Applications:

• In Medicine: Glucose is used as a tonic, supplying energy to the body.
• In Industry: Used for silvering mirrors, producing ethyl alcohol.
• In Food: It is the main ingredient in the production of confectionery and soft drinks.

Note:

• Glucose has a lower sweetness than sugarcane (sucrose).
• Blood glucose levels are regulated by the hormone insulin.
• Glucose is the main energy source for the body.

II. Fructose (C6H12O6)

1. Concept:

• Fructose is a type of monosaccharide, commonly called fruit sugar.
• It is found in fruits like pineapple, mango, honey, etc.
• In honey, fructose accounts for about 40%.

2. Structure:

• Open Chain: Fructose has an open chain structural formula of CH2OH-CO-(CHOH)3-CH2OH.
• Ring Structure: Fructose mainly exists in a 5-membered ring form (furanose).

3. Properties:

• Ketone Properties: Fructose has a C=O group at C2, exhibiting the properties of a carbonyl group.
• Properties of Polyhydric Alcohol: Fructose has 5 -OH groups, exhibiting the properties of polyhydric alcohol.
• Conversion in Alkaline Medium: Fructose and glucose can be interconverted in an alkaline medium.

4. Applications:

• In Food: Fructose has a higher sweetness than glucose and is used as a sweetener in food production.

Note:

• Fructose is the simplest sugar that can be directly converted into energy.
• Fructose has a higher sweetness than glucose and sucrose.

III. Comparison between Glucose and Fructose:

• Structure: Both have the molecular formula C6H12O6, but their open chain and ring structures differ.
• Properties: Glucose is an aldehyde, fructose is a ketone.
• Sweetness: Fructose is sweeter than glucose.
• Conversion: Both can be interconverted in an alkaline medium.

IV. Distinguishing between Glucose, Fructose, Glycerol, Ethanol, and Acetic Acid:

• Cu(OH)2:
  • Glucose and fructose form a blue complex.
  • Glycerol forms a stable blue complex.
  • Ethanol and acetic acid do not react.

V. Some characteristic reactions:

• Glucose reacting with H2: Glucose is reduced to form sorbitol.
• Glucose reacting with AgNO3/NH3: Glucose is oxidized to form silver.
• Glucose reacting with Br2/H2O: Glucose is oxidized to form gluconic acid.
• Fructose reacting with Cu(OH)2: Fructose forms a blue complex.
• Fructose reacting with H2: Fructose is reduced to form sorbitol.

Note:

• Glucose and fructose are two simple sugars that play important roles in the body’s metabolism.
• Understanding the properties and applications of these two sugars provides us with knowledge of nutrition and health.