Class 12 Chemistry – Williamson Synthesis

1. Introduction

• Williamson synthesis is a method used to prepare ethers.

• It is one of the most important methods for making both symmetrical and asymmetrical ethers.

• Named after Alexander William Williamson, a British chemist.

2. Principle

• The reaction involves reacting an alkoxide ion (R–O⁻) with an alkyl halide (R'–X).

• The alkoxide acts as a nucleophile and substitutes the halogen in the alkyl halide.

• This reaction works best with primary alkyl halides; secondary and tertiary may give side reactions.

3. Mechanism (Conceptual)

1. Formation of Alkoxide: A metal hydroxide reacts with an alcohol to form the alkoxide.

2. Nucleophilic Attack: The alkoxide attacks the carbon atom of the alkyl halide.

3. Ether Formation: Halogen is displaced, forming the ether product.

4. Types of Ethers Prepared

• Symmetrical Ethers: Both alkyl groups are the same (e.g., ethyl ether).

• Asymmetrical Ethers: Alkyl groups are different (e.g., methyl ethyl ether).

5. Conditions for Williamson Synthesis

• Alkyl halide should preferably be primary.

• Alkoxide should be strong nucleophile.

• Solvent should be aprotic, such as alcohol or ether, to prevent side reactions.

6. Importance and Applications

• Widely used method for preparing ethers in laboratory and industry.

• Helps in synthesis of various pharmaceutical intermediates.

• Can be used to produce both symmetrical and asymmetrical ethers selectively.

7. Key Points to Remember

• Involves alkoxide + alkyl halide → ether.

• Works best with primary alkyl halides.

• Can produce symmetrical or asymmetrical ethers.

• Alkoxide acts as a nucleophile, halide is the leaving group.

• Simple, efficient, and widely used ether synthesis method.