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


For preparation of Phenol visit http://entrancechemistry.blogspot.com/2012/02/prepration-of-phenol.html