Preparation of Ethers

Williamson Synthesis (most important): R–O–Na + X–R' → R–O–R' + NaX. Primary alkyl halide is preferred (SN2 mechanism; 2° or 3° alkyl halide gives elimination).

Acid-catalysed dehydration of alcohols: 

\[\ce{2R - OH ->[H2SO4, 413K] R - O - R + H2O}\]

(works best for symmetrical ethers)

From alcohols by catalytic dehydration: 

\[\ce{2C2H5OH ->[Al2O3, 513-523K] C2H5 - O - C2H5 + H2O}\]

Alkoxy mercuration-demercuration: \[\begin{array}{cc}
\phantom{}\ce{CH3 - CH = CH2 + C2H5OH + Hg(OCOCF3)2 -> CH3 - CH - CH2 - HgOCOCF3 ->[NaBH4/OH^{-}] CH3 - CH - CH3}\\
\phantom{................................................................................}|\phantom{.....................................................................}|\phantom{.}\\
\phantom{............................................................................................}\ce{OC2H5}\phantom{...........................................................}\ce{O-C2H5}\phantom{.}
\end{array}\]