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

12. Alcohols, Ethers, Epoxides and Thiols

Williamson Ether Synthesis

Organic Chemistry

12. Alcohols, Ethers, Epoxides and Thiols

Williamson Ether Synthesis

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Problem 105

Textbook Question

The reaction of alkoxides with haloalkanes is not a viable way to form ethers. (a) Why? (b) Why can thioethers be formed by an analogous reaction?

Verified step by step guidance

Step 1: Understand the reaction mechanism involved in the formation of ethers and thioethers. The reaction of alkoxides with haloalkanes typically follows an SN2 mechanism, where the nucleophile attacks the electrophilic carbon attached to the halogen.

Step 2: Consider the nature of the nucleophile. Alkoxides are strong bases and can lead to elimination reactions instead of substitution, especially with secondary or tertiary haloalkanes, due to steric hindrance and the formation of more stable alkenes.

Step 3: Analyze the reaction conditions. In the case of alkoxides reacting with haloalkanes, the strong basic nature of alkoxides can lead to the formation of alkenes via elimination rather than ethers via substitution.

Step 4: Compare the nucleophilicity and basicity of alkoxides and thiolates. Thiolates are less basic and more nucleophilic compared to alkoxides, which makes them more suitable for substitution reactions with haloalkanes, leading to the formation of thioethers.

Step 5: Conclude why thioethers can be formed. The lower basicity and higher nucleophilicity of thiolates allow them to effectively participate in SN2 reactions with haloalkanes, forming thioethers without competing elimination reactions.

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Key Concepts

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

Alkoxide Reactivity

Alkoxides are strong nucleophiles that can react with haloalkanes through nucleophilic substitution. However, the reaction often leads to elimination rather than substitution, especially with secondary and tertiary haloalkanes, making ether formation inefficient. This is due to steric hindrance and the stability of the resulting alkene.

Ethers vs. Thioethers

Ethers are formed by the reaction of alcohols with alkyl halides, while thioethers (or sulfides) can be formed through a similar reaction involving thiols. The sulfur atom in thioethers is larger and less electronegative than oxygen, allowing for more favorable nucleophilic substitution reactions with haloalkanes, thus facilitating thioether formation.

Nucleophilic Substitution Mechanisms

Nucleophilic substitution can occur via two main mechanisms: SN1 and SN2. SN2 reactions involve a single concerted step where the nucleophile attacks the electrophile, while SN1 involves a two-step process with a carbocation intermediate. The choice of mechanism affects the feasibility of ether formation from alkoxides and the successful formation of thioethers.

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Related Practice

Textbook Question

(a) Show how ethanol and cyclohexanol may be used to synthesize cyclohexyl ethyl ether (tosylation followed by the Williamson ether synthesis).

(b) Why can't we synthesize this product simply by mixing the two alcohols, adding some sulfuric acid, and heating?

Textbook Question

A good Williamson synthesis of ethyl methyl ether would be

What is wrong with the following proposed synthesis of ethyl methyl ether? First, ethanol is treated with acid to protonate the hydroxy group (making it a good leaving group), and then sodium methoxide is added to displace water.

Textbook Question

Phenols (pK_a ≈ 10) are more acidic than other alcohols, so they are easily deprotonated by sodium hydroxide or potassium hydroxide. The anions of phenols (phenoxide ions) can be used in the Williamson ether synthesis, especially with very reactive alkylating reagents such as dimethyl sulfate. Using phenol, dimethyl sulfate, and other necessary reagents, show how you would synthesize methyl phenyl ether.

Textbook Question

Identify the two possible combinations of haloalkane and alkoxide that can be used to make the following ether.

Textbook Question

How could the reaction in Figure 13.67(b) be modified to produce the following ether?

Textbook Question

Show how the following ethers might be synthesized using (1) alkoxymercuration– demercuration and (2) the Williamson synthesis. (When one of these methods cannot be used for the given ether, point out why it will not work.)

a. 2-methoxybutane

b. ethyl cyclohexyl ether

c. 1-methoxy-2-methylcyclopentane

Textbook Question

There are two different ways of making 2-ethoxyoctane from octan-2-ol using the Williamson ether synthesis. When pure (–)-octan-2-ol of specific rotation -8.24° is treated with sodium metal and then ethyl iodide, the product is 2-ethoxyoctane with a specific rotation of -15.6°. When pure (–)-octan-2-ol is treated with tosyl chloride and pyridine and then with sodium ethoxide, the product is also 2-ethoxyoctane. Predict the rotation of the 2-ethoxyoctane made using the tosylation/sodium ethoxide procedure, and propose a detailed mechanism to support your prediction.

Textbook Question

Propose a Williamson synthesis of 3-butoxy-1,1-dimethylcyclohexane from 3,3-dimethyl-cyclohexanol and butan-1-ol.

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