Dehydration Reactions with Sugars

Dehydration Reactions with Sugars

• Concentrated sulfuric acid acts as a dehydrating agent, removing water molecules from sugars.
• Penta-sugars (5-carbon sugars) react with concentrated sulfuric acid to produce furfural.
• Hexa-sugars (6-carbon sugars) react with concentrated sulfuric acid to produce hydroxymethylfurfural.
• Furfural and hydroxymethylfurfural react with α-naphthol, forming a violet compound visible as a ring between separation surfaces.

Molsch Reaction

• Fructose or glucose reacts with dilute hydrochloric acid (3N or 12%) to form 5-hydroxymethylfurfural.
• The 5-hydroxymethylfurfural then reacts with resorcinol.

Bial's Test

• Bial's test specifically detects pentose monosaccharides.
• Concentrated hydrochloric acid dehydrates pentose sugars, producing furfural.
• Furfural reacts with orcinol in the presence of ferric ions to produce a blue-green complex.

Concentrated Sulfuric Acid and Sugars

• Concentrated sulfuric acid is a dehydrating agent, removing water molecules from penta- and hexa-sugars.
• This reaction produces furfural from penta-sugars and hydroxymethylfurfural from hexa-sugars.
• Furfural and hydroxymethylfurfural can react with α-naphthol, resulting in a violet compound.
• This reaction is observable as a ring between the two separation surfaces.

Molsch Reaction

• The Molsch reaction is analogous to the reaction with concentrated sulfuric acid.
• In the Molsch reaction, fructose or glucose reacts with hydrochloric acid (3 N or 12%) to produce 5-hydroxymethylfurfural.
• 5-hydroxymethylfurfural then reacts with resorcinol.

Bial's Test

• Bial's test is specific for pentose monosaccharides.
• Concentrated hydrochloric acid removes water molecules from pentose sugars, forming furfural.
• Furfural reacts with orcinol in the presence of ferric ions, producing a blue-green complex.