Preparation of ethers by acid - catalysed dehydration of secondary and tertiary alcohols is not a suitable method. Give reason.

Explanation

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

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