Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

28. Carbohydrates

Monosaccharides - Acylation

Organic Chemistry

28. Carbohydrates

Monosaccharides - Acylation

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2:58 minutes

Problem 28a

Textbook Question

Predict the products formed when the following sugars react with excess acetic anhydride and pyridine.
(a) α-D-glucopyranose

Verified step by step guidance

Identify the functional groups present in α-D-glucopyranose. It contains hydroxyl (-OH) groups on the sugar ring and an anomeric hydroxyl group at the C1 position.

Understand the role of acetic anhydride and pyridine. Acetic anhydride is an acetylating agent that reacts with hydroxyl groups to form acetate esters, while pyridine acts as a base to neutralize the byproduct (acetic acid) and facilitate the reaction.

Determine the number of hydroxyl groups available for reaction. In α-D-glucopyranose, there are five hydroxyl groups: one at the anomeric carbon (C1) and four on the other carbons of the sugar ring.

Predict the reaction outcome. Each hydroxyl group will react with acetic anhydride to form an acetate ester. The product will be a fully acetylated sugar, where all hydroxyl groups are replaced with acetate groups (-OCOCH₃).

Draw the structure of the product. The α-D-glucopyranose will now have acetate groups attached to all five positions where hydroxyl groups were originally present, maintaining the pyranose ring structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acetic Anhydride Reactivity

Acetic anhydride is a powerful acetylating agent used to introduce acetyl groups into organic molecules. In the presence of a base like pyridine, it reacts with hydroxyl groups on sugars, converting them into acetylated derivatives. This reaction is crucial for modifying sugars to improve their solubility and stability in various chemical processes.

Pyridine as a Catalyst

Pyridine acts as a base and catalyst in the acetylation reaction, facilitating the nucleophilic attack of the sugar's hydroxyl groups on the acetic anhydride. Its basicity helps to deprotonate the hydroxyl groups, making them more nucleophilic and enhancing the reaction rate. Understanding the role of pyridine is essential for predicting the outcome of the reaction.

Sugar Structure and Reactivity

The structure of sugars, particularly their anomeric carbon and hydroxyl groups, significantly influences their reactivity. In the case of α-D-glucopyranose, the configuration at the anomeric carbon determines the specific products formed during acetylation. Recognizing how different hydroxyl groups on the sugar can react helps in predicting the final acetylated products.

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