Williamson's synthesis of Ethers

Preparation of ethers using sodium alkoxide

This is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers. In this method, ethers are prepared by heating an alkyl halide with sodium alkoxide.

Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by this method. The reaction involves a nucleophilic substitution of halide ion by an alkoxide ion.

Thus, good results are obtained if the alkyl halide is primary. If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed. For example, the reaction of CH3CONa with (CH3)3 C-Br gives exclusively 2 -methyl propene.

It is because alkoxides are not only nucleophiles but also strong bases. They react with alkyl halides leading to elimination reactions.

Since halogen attached to the benzene ring is not reactive, in order to prepare an alkyl aryl ether, a mixture of alkyl halide and sodium phenoxide must be heated.

For example, ethyl phenyl ether is obtained by heating a mixture of ethyl iodide and sodium phenoxide.

No comments:

Post a Comment