Preparation of Ethers

Preparation of Ethers by Dehydration of Alcohols

When excess of a primary alcohol is heated with protonic acids like conc.H2SO4 or H3PO4 at 413 K , it undergoes dehydration to form an ether.

2R - OH (Alcohol) -----(conc.H2SO4, 413K)-----> R-O-R (Ether) + H2O

2C2H5 OH (Ethanol)-----(conc.H2SO4, 413K)-----> C2H5-O-C2H5 (Diethyl ether) + H2O

But this reaction cannot be used for the preparation of unsymmetrical ethers.

The formation of reaction product depends on the reaction conditions. At high temperature, if excess of acid is used dehydration occurs in a different way to form an alkene. For example, ethanol when heated with conc.H2SO4 at 440K undergoes dehydration to give ethylene.

CH3 CH2 OH -----(conc.H2SO4, 413K)-----> CH2 = CH2 + H2O

The dehydration of secondary and tertiary alcohols to the corresponding ethers is unsuccessful as alkenes are formed easily in these reactions.

The dehydration of alcohols can also be brought about by passing the vapours of the alcohol under pressure over a heated catalyst like alumina or thoria at 523 K.

2C2H5 OH (Ethanol) -----(conc.H2SO4, 523K)-----> C2H5-O-C2H5 (Diethyl ether) + H2O

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