Question

Carry out the following conversion
Ethanal to But-2-enal

Hint:

Aldol condensation is used to form conjugated enals, and here, it is used to synthesize But-2-enal from Ethanal.

Answer 1

To convert ethanal (CH₃CHO) to but-2-enal (CH₃CH=CHCHO), we can follow a series of organic reactions involving aldol condensation and dehydration.

1. Aldol Condensation:
Ethanal undergoes aldol condensation in the presence of a dilute base (e.g., NaOH) to form 3-hydroxybutanal (aldol).

$ 2 \, \text{CH}_3\text{CHO} \xrightarrow{\text{NaOH}} \text{CH}_3\text{CH(OH)CH}_2\text{CHO} $

2. Dehydration:
The 3-hydroxybutanal intermediate is then dehydrated (elimination of water) in the presence of an acid (e.g., H₂SO₄) or heat to form but-2-enal (crotonaldehyde).

$ \text{CH}_3\text{CH(OH)CH}_2\text{CHO} \xrightarrow{\text{H}^+ \text{ or } \Delta} \text{CH}_3\text{CH=CHCHO} + \text{H}_2\text{O} $

Summary of the Conversion:
Ethanal → (Aldol Condensation) → 3-Hydroxybutanal → (Dehydration) → But-2-enal

Final Answer:
The conversion of ethanal to but-2-enal is achieved via $\boxed{\text{aldol condensation followed by dehydration}}$.