Ethers from Alcohols: Alcohol Dehydration and Williamson Ether Synthesis

The two most common methods for preparing ethers from alcohols are alcohol dehydration and Williamson ether synthesis.

Alcohol dehydration is used for the industrial preparation of ethers. The method involves acid-catalyzed dehydration of alcohols via the S_N2 mechanism.

Consider the dehydration of ethanol in the presence of sulfuric acid to give diethyl ether.

The reaction begins with a proton transfer from the acid catalyst to the hydroxyl group of ethanol, forming an oxonium ion. The proton transfer converts hydroxyl, a poor leaving group, into an oxonium ion, a better leaving group.

Subsequently, a second ethanol molecule, acting as a nucleophile, attacks the oxonium ion in an S_N2 reaction and displaces a water molecule, forming a new oxonium ion.

Finally, proton transfer from the new oxonium ion to water completes the reaction, giving ethoxyethane as the final product.

The alcohol dehydration method is limited to the preparation of symmetrical ethers derived from primary alcohols. Secondary and tertiary alcohols cannot be used because they dehydrate to alkenes.

Additionally, the method is unfit for the preparation of asymmetrical ethers because it yields a mixture of ethers.

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