Williamson synthesis
An alkyl halide reacts with a sodium alkoxide (or phenoxide) to give an ether.
BromoethaneCH₃CH₂BrHaloalkane - Step 1
CH₃CH₂ONa (sodium ethoxide)
EthoxyethaneCH₃CH₂OCH₂CH₃Ether
How it works
- The alkoxide ion is a strong nucleophile.
- It attacks the alkyl halide by SN₂ and displaces the halide.
- The ether and NaX are formed.
What it makes
Symmetrical and unsymmetrical ethers, and aryl alkyl ethers such as anisole.
Where it fails
The halide must be primary. Secondary and tertiary halides eliminate to alkenes. For a hindered ether, put the bulky group on the alkoxide.
Class 12, Chapter 7 Alcohols, Phenols and Ethers
Williamson synthesis: quick answers
Why does a tertiary alkyl halide fail?
The alkoxide acts as a base and causes elimination, giving an alkene.
How do you make anisole by this route?
Treat phenol with NaOH to get sodium phenoxide, then add CH3I.
How do you make tert-butyl methyl ether?
Use sodium tert-butoxide with CH3Br, not sodium methoxide with tert-butyl bromide.