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

Disaccharide

Organic Chemistry

28. Carbohydrates

Disaccharide

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Problem 42

Textbook Question

Cellulose is converted to cellulose acetate by treatment with acetic anhydride and pyridine. Cellulose acetate is soluble in common organic solvents, and it is easily dissolved and spun into fibers. Show the structure of cellulose acetate.

Verified step by step guidance

Understand the structure of cellulose: Cellulose is a polysaccharide composed of β-D-glucose units linked by β-1,4-glycosidic bonds. Each glucose unit contains three hydroxyl (-OH) groups at positions C2, C3, and C6.

Recognize the role of acetic anhydride: Acetic anhydride reacts with hydroxyl groups in the presence of a base (pyridine) to form acetate esters. This reaction replaces the hydroxyl groups (-OH) with acetyl groups (-OCOCH₃).

Identify the reaction mechanism: The reaction proceeds via nucleophilic attack of the hydroxyl oxygen on the carbonyl carbon of acetic anhydride, forming an ester bond and releasing acetic acid as a byproduct.

Determine the structure of cellulose acetate: Replace the hydroxyl groups on the glucose units of cellulose with acetyl groups (-OCOCH₃). The degree of substitution (DS) can vary, meaning not all hydroxyl groups may be acetylated. For full acetylation, all three hydroxyl groups on each glucose unit are replaced with acetyl groups.

Draw the structure: Represent the repeating unit of cellulose acetate, showing the β-1,4-glycosidic linkage between glucose units and the acetyl groups attached to the C2, C3, and C6 positions of each glucose unit. Ensure the stereochemistry of the glucose units is preserved.

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Key Concepts

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

Cellulose Structure

Cellulose is a polysaccharide composed of linear chains of β-D-glucose units linked by β(1→4) glycosidic bonds. This structure provides cellulose with high tensile strength and makes it insoluble in water. Understanding the basic structure of cellulose is crucial for comprehending how it can be chemically modified to form cellulose acetate.

Acetylation Reaction

Acetylation is a chemical reaction that introduces an acetyl group (–COCH3) into a compound. In the case of cellulose acetate, acetic anhydride reacts with the hydroxyl groups of cellulose, replacing some of them with acetyl groups. This modification alters the solubility and thermal properties of cellulose, making it suitable for applications like fiber production.

Solubility of Polymers

The solubility of polymers like cellulose acetate in organic solvents is influenced by their chemical structure and the presence of functional groups. The introduction of acetyl groups in cellulose acetate reduces hydrogen bonding between polymer chains, enhancing its solubility in solvents such as acetone and chloroform. This property is essential for processing cellulose acetate into fibers and films.

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