The reaction of an alkyl halide with sodium alkoxide to form an ether is known as the Williamson ether synthesis.

Reaction: $R-X + R'-ONa \rightarrow R-O-R' + NaX$

It is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers. The reaction involves a nucleophilic substitution ($S_N2$) of the halide ion by the alkoxide ion.