The Williamson ether synthesis is a chemical reaction important to organic chemistry. The reaction makes an ether from an organohalide and an alkoxide. It is named after its discoverer, Alexander Williamson. Williamson's accidental discovery of the ether synthesis helped people understand the structure of ethers and alcohols.
The Williamson synthesis is the main way that chemists make unsymmetrical ethers, which can't be made by dehydration of alcohols.
The Williamson ether synthesis is an example of an SN2 reaction. The alkoxide is made in situ using an alcohol and a strong base like sodium hydride. The alkoxide then acts as a nucleophile that attacks the electrophilic carbon atom of the halide. Due to steric effects, the Williamson synthesis is normally done with a bigger alkoxide and smaller halide.
Alexander Williamson discovered the Williamson ether synthesis accidentally when trying to make heavier alcohols from ethanol (as potassium ethoxide) and ethyl iodide. Instead of the expected butanol, the reaction produced diethyl ether:
Before Williamson, chemists had two different theories about the relationship between alcohols and ethers. It was well known that ether could be made by dehydration of alcohols using sulfuric acid, and that diethyl ether had the chemical formula C4H10O, but chemists could not agree on whether alcohols were a reaction product of ether and water (which would give ethanol a formula of C4H12O2) or ethers were a reaction product from the elimination of water from two molecules of alcohol (which would give ethanol a formula of C2H6O). Because Williamson's reaction made ether from an alkoxide without giving off any other chemicals with oxygen, it showed that alcohols can't have more oxygen than ethers.