Question

What type of mechanism is followed by dehydration of alcohol to form ether?

• A. Nucleophilic substitution unimolecular reaction
• B. Nucleophilic substitution bimolecular reaction
• C. Electrophilic substitution reaction
• D. Electrophilic addition reaction

Hint:

Dehydration of primary alcohols to ethers goes by SN2: one alcohol attacks a protonated alcohol.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
At about 413 K with excess alcohol and an acid catalyst, primary alcohols form ethers by bimolecular dehydration.

Step 2: Mechanism:
Step 1: the alcohol is protonated to \(\text{ROH}_2^+\). Step 2: a second alcohol molecule uses its lone pair on O to attack the carbon of the protonated alcohol, pushing out water. Step 3: loss of a proton gives \(\text{R-O-R}\).

Step 3: Name the mechanism:
Step 2 involves a nucleophile attacking in the same step in which the leaving group leaves, which is nucleophilic substitution bimolecular (\(\text{S}_\text{N}2\)).

Step 4: Why the other options are wrong.
\(\text{S}_\text{N}1\) would need a stable carbocation, which a primary alcohol does not give. Electrophilic substitution and addition are reactions of aromatic rings and alkenes.

Final Answer:
Dehydration to ether follows the SN2 mechanism. \[ \boxed{\text{(B) }\text{Nucleophilic substitution bimolecular reaction}} \]