13 Reactions of Ethers

13.3 Reactions of Ethers | Organic Chemistry

Introduction

This lesson explores the reactions of ethers, focusing mainly on crown ethers and the acidic cleavage of ethers.

Main Points

• Crown Ethers:

- Structure: Crown ethers are cyclic polyethers that solvate alkali metal cations. The size of the crown ether determines the size of the cation it can solvate.

- Naming: Based on the total number of atoms and the number of oxygens (e.g., 12-crown-4, 15-crown-5, 18-crown-6).

- Utility: Crown ethers increase the solubility of alkali metal salts in organic solvents, making them useful for SN2 reactions.

• Acidic Cleavage of Ethers:

- Process: Undergoes in strong acids (HCl, HBr, HI) leading to the substitution of the ether oxygen with a halogen.

- Mechanism: Involves the protonation of the ether followed by SN1 or SN2 reactions depending on the substituents. Secondary ethers usually follow SN1, while primary ethers follow SN2.

- Phenyl Ethers: The cleavage of phenyl ethers leads to phenol and an alkyl halide; the C-O bond with the phenyl group cannot be cleaved due to its sp2 hybridization.

Conclusion

• Ethers in Organic Synthesis: Ethers generally have limited reactivity, making them suitable solvents for many reactions. The acidic cleavage is a notable exception, especially useful for converting ethers to alkyl halides.
• Significance of Crown Ethers: Crown ethers play a crucial role in enhancing the reactivity of alkali metal salts in organic synthesis.