Study Notes on Ethers, Epoxides, Thiols, and Sulfides

Organic Chemistry

Chapter 18: Ethers and Epoxides; Thiols and Sulfides

• Source: OpenStax, Tenth Edition

Homework

• Problems: 19 - 55

Chapter Contents

1. 18.1 Names and Properties of Ethers

2. 18.2 Preparing Ethers

3. 18.3 Reactions of Ethers: Acidic Cleavage

4. 18.4 Cyclic Ethers: Epoxides

5. 18.5 Reactions of Epoxides: Ring-Opening

6. 18.6 Crown Ethers

7. 18.7 Thiols and Sulfides

8. 18.8 Spectroscopy of Ethers

9. Preview of Carbonyl Chemistry

18.1 Names and Properties of Ethers

• Examples of Ethers:

  • Diethyl Ether: $ext{C}<em>4 ext{H}</em>{10} ext{O}$

  • Structure: $ext{CH}_3 ext{CH}_2 ext{O} ext{CH}_2 ext{CH}_3$

  • Anisole: $ext{C}_7 ext{H}_8 ext{O}$

  • Structure: $ext{C}_6 ext{H}_5 ext{O} ext{CH}_3$

  • Tetrahydrofuran: $ext{C}_4 ext{H}_8 ext{O}$

  • Structure: A five-membered ether ring

18.2 Preparing Ethers

• Key Methods:

  • Williamson Ether Synthesis:

  • Mechanism: Utilizes an $ext{SN2}$ reaction to form ethers.

  • Requires alkoxide ion as a nucleophile.

  • Alkoxymercuration:

  • Involves the reaction of alkenes with mercury reagent, generating ethers.

18.3 Reactions of Ethers: Acidic Cleavage

• Mechanism Overview: Ethers can be cleaved in acidic conditions to form alcohols and alkyl halides.

• Example Reaction:

  • Reaction of ethyl phenyl ether with HBr leads to phenol and bromoethane upon refluxing.

  • $ext{C}_2 ext{H}_5 ext{O} ext{C}_6 ext{H}_5 + ext{HBr} <br>ightarrow ext{C}_6 ext{H}_5 ext{OH} + ext{C}_2 ext{H}_5 ext{Br}$

18.4 Cyclic Ethers: Epoxides

• Structure and Formation:

  • Epoxides are three-membered cyclic ethers and are reactive due to ring strain.

  • Can be formed from alkenes via oxidation reactions.

18.5 Reactions of Epoxides: Ring-Opening

• Mechanisms:

  • Acid-Catalyzed Opening:

  • Epoxidation reactions of alkenes can be catalyzed by acid to open the ring and create alcohols.

  • Base-Catalyzed Opening:

  • Uses a nucleophile to attack one of the carbons of the epoxide, leading to alcohol formation.

18.6 Crown Ethers

• Definition and Examples:

  • Crown ethers are cyclic polyethers that can form complexes with cations.

  • Example: 18-Crown-6 ether efficiently binds potassium ions.

18.7 Thiols and Sulfides

• Thiols:

  • General structure: $ext{R-SH}$, where R is an alkyl group.

  • Sulfides:

  • General structure: $ext{R-S-R'}$, where R and R' can be different alkyl groups.

18.8 Spectroscopy of Ethers

• Infrared Spectroscopy:

  • Ethers display a characteristic $C-O$ stretch in IR spectra.

• Example of diethyl ether: Peak observed around 1000-1200 cm $^{-1}$.

Preview of Carbonyl Chemistry

• Overview: Carbonyl compounds display unique chemical behaviors due to the presence of the carbonyl functional group.

Detailed Mechanisms and Examples

Williamson Ether Synthesis

• Mechanism Steps:

  1. Formation of Alkoxide Ion:

  • Reaction of alcohol with a base:

    • $ext{R-OH} + ext{NaH} <br>ightarrow ext{R-O}^- ext{Na}^+$

  1. Nucleophilic Attack: Alkoxide attacks a primary alkyl halide via an $ext{SN2}$ path, forming the ether.

  • Example:

  • Cyclopentyl methyl ether synthesized with 74% yield.

Worked Example 18.1: Synthesizing Ethyl Phenyl Ether

• Methods Considered: Williamson synthesis vs. alkoxymercuration.

• Chosen Method:

  • Williamson synthesis preferred due to reactivity of primary alcohols.

• Strategy:

  1. Identify groups on ether (ethyl and phenyl)

  2. Select appropriate alkyl halide for reaction.

Properties and Spectroscopy of Ethers and Thiols

• Ethers tend to have lower boiling points than alcohols due to lack of hydrogen bonding.

• Thiols: Characteristic odor, used in flavorings and as antioxidants.

• Sulfides: Often have influential roles in biochemical processes.

Further Reactions Involving Ethers and Thiols

• Disulfide Formation: Oxidation of thiols leads to the formation of disulfides:

  • $ext{2 R-SH} <br>ightarrow ext{R-S-S-R} + ext{H}_2 ext{O}$

  • Applications in protein structure and function.

Conclusion of Topics

• This chapter emphasizes the reactivity and importance of ethers, epoxides, thiols, and sulfides in organic chemistry through their synthesis and various functional properties. The understanding of these compounds lays the groundwork for their applications in both synthetic and biological processes.