Maltose: Oxidation, Methylation & Hydrolysis Reactions — Notes PDF
- Maltose = α-D-Glcp-(1→4)-α-D-Glcp (reducing disaccharide)
- Oxidation (Br₂/H₂O): C1–CHO → –COOH → Maltobionic acid
- Methylation → hydrolysis: 2,3,4,6-tetra + 2,3,6-tri-methyl glucose
- Free C4–OH in tri-methyl glucose confirms 1→4 linkage
- Hydrolysis (maltase/H⁺): gives 2× α-D-glucose → homodisaccharide
Maltose — Structure and Chemical Reactions
Structure: The C1 of the non-reducing glucose is linked via –O– to C4 of the reducing glucose.
The free –OH at C1 of the reducing end can open to give an aldehyde → explains all reducing-sugar reactions.
Total free –OH groups = 8 (before any reaction).
1. Oxidation of Maltose
Reagent: Bromine water (Br₂/H₂O) — mild oxidant
Inference from Oxidation:
2. Methylation of Maltose
Reagent: Methyl iodide (CH₃I) + Silver oxide (Ag₂O) — Purdie's method
Then: Acid Hydrolysis of Octa-O-methylmaltose
2,3,4,6-Tetra-O-methyl glucose → from the non-reducing end
All 4 free OH positions (C2, C3, C4, C6) were methylated.
C1 was part of the glycosidic bond → its –O– was NOT free → NOT methylated.
2,3,6-Tri-O-methyl glucose → from the reducing end
Only 3 free OH positions (C2, C3, C6) were methylated.
C1 was free (anomeric –OH) → got methylated, but C1–OCH₃ is lost on acid hydrolysis → free C1–OH restored.
C4–OH was NOT methylated because it was involved in the glycosidic bond → freed on hydrolysis.
Inference from Methylation:
3. Hydrolysis of Maltose
Reagent: Dilute HCl / H₂SO₄ (acid hydrolysis) OR Maltase enzyme (specific for α-linkages)
Inference from Hydrolysis:
Summary of Inferences
| Reaction | Reagent | Product | Key Inference |
|---|---|---|---|
| Oxidation | Br₂/H₂O | Maltobionic acid | Maltose is a reducing sugar — free C1 anomeric –OH at reducing end |
| Methylation + Hydrolysis | CH₃I/Ag₂O then H₃O⁺ | 2,3,4,6-tetra + 2,3,6-tri-O-methyl glucose | Linkage is C1–C4 (C4 of reducing end was bonded, not free) |
| Hydrolysis | Dilute HCl or maltase | 2 × α-D-Glucose | Maltose is a homodisaccharide with an α-glycosidic bond |
Complete Reaction Scheme at a Glance
- Maltose = α-D-Glcp-(1→4)-α-D-Glcp (reducing disaccharide)
- Oxidation (Br₂/H₂O): C1–CHO → –COOH → Maltobionic acid
- Methylation → hydrolysis: 2,3,4,6-tetra + 2,3,6-tri-methyl glucose
- Free C4–OH in tri-methyl glucose confirms 1→4 linkage
- Hydrolysis (maltase/H⁺): gives 2× α-D-glucose → homodisaccharide
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About Maltose: Oxidation, Methylation & Hydrolysis Reactions — Notes PDF
Maltose: Oxidation, Methylation & Hydrolysis Reactions — Notes PDF is a fundamental concept in organic chemistry. Understanding the mechanisms, reaction conditions, and stereo-chemical outcomes is crucial for mastering organic chemistry. Our curated resources provide step-by-step visualizations to help you excel.
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Practice MCQs
Maltose is a reducing sugar. What structural feature makes it so?
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Maltose:
Oxidation, Methylation & Hydrolysis Reactions — Notes PDF FAQ
Maltose is a reducing sugar because one of its glucose units has a free anomeric carbon (a hemiacetal group) that is not locked in a glycosidic bond, allowing it to ring-open and undergo oxidation.
It proves the presence of a 1→4 glycosidic linkage. After methylation and hydrolysis, the C4 position on the reducing glucose unit is the only unmethylated hydroxyl group, proving it was previously occupied by the glycosidic bond.
Complete hydrolysis of maltose (using acid or the enzyme maltase) breaks the alpha-(1→4) glycosidic bond, yielding two separate molecules of alpha-D-glucose.