Question

Consider the following steps :
Step I Formation of ethene by the elimination of a proton.
Step II Formation of protonated alcohol.
Step III Formation of carbocation.
Arrange the following steps in a sequence which are involved in the mechanism of dehydration of ethanol.

• A. $I,II$ and $III$
• B. $II,I$ and $III$
• C. $II,III$ and $I$
• D. $I,III$ and $II$

Answer 1

Answer: (C)

The mechanism of dehydration of ethanol involves the following steps :
Mechanism
Step I Formation of protonated alcohol.

Step II Formation of carbocation : It is the slowest step and hence, the rate determining step of the reaction.

Step III Formation of ethene by elimination of a proton.

The acid used in step I is released in step III.
To drive the equilibrium to the right, ethene is removed as it is formed.