Question

Preparation of ethers by acid dehydration of secondary or tetiary alcohols is not a suitable method. Give reason.

Answer 1

Acid-catalysed dehydratrion of `1^(@)` alcohols to ethers occurs by `SN^(2)` reaction involving nucleophilic attack by the alcohol molecule on the protonated alcohol molecule.

Under these conditions, `2^(@)` and `3^(@)` alcohols, however, give alkenes rathenes than ethers. The reason being that due, to steric hindrance, nucleophilic attack by the alcohol molecule on the protonatedc alcohol molecule does not occur. Insted protonated `2^(@)` and `3^(@)` alcohols lose a molecule of water form stable `2^(@)` and `3^(@)` carbocations. These carbonations prefer to lose a proton to form alkenes rather than undergoing nucleophilic attack by alcohol molecules to form ethers.


Similarly, `3^(@)` alcohols give alkenes rather than ethers.