Question

Question: Acid-catalyzed dehydration of β-hydroxy carbonyl compounds occurs by the mechanism discussed in Section 9.8. With this in mind, draw a stepwise mechanism for the following reaction.

Short answer

Answer

Step-by-step solution

Dehydration reaction

The reverse of the dehydration reaction is hydration reaction. Hydration means addition of water, whereas dehydration means removal of water.

Alkene is formed in dehydration of alcohol, while alcohol is formed in hydration of alkene.

Mechanism of the reaction

In the first step of the reaction, oxygen of hydroxyl group abstracts a proton from acid following removing of water to form carbocation.

In the next step, the hydrogen sulfate ion abstracts the alpha hydrogen and results in the formation of (E)-but-2-enal.

The mechanism is shown below:

Mechanism of the reaction