Animated Solution for Chemistry - Hydrocarbons: But-2-ene on reaction with alkaline ${\text{KMnO}}_4$ at elevated temperature followed by acidification will give

When you encounter an organic chemistry problem, the first and most crucial step is to carefully analyze the reagents. In this question, we are dealing with But-2-ene reacting with alkaline ${\text{KMnO}}_4$ at an elevated temperature, followed by an acidification step.

What does this specific combination do? Potassium permanganate (${\text{KMnO}}_4$) is a well-known oxidizing agent. However, its behavior changes drastically depending on the conditions. If we were using cold, dilute ${\text{KMnO}}_4$ (often called Baeyer's reagent), it would gently add two hydroxyl ($-\text{OH}$) groups across the double bond, forming a vicinal diol. But here, the keyword is elevated temperature. Hot alkaline ${\text{KMnO}}_4$ is a vigorous, aggressive oxidizing agent that doesn't just add to the double bond—it completely shatters it.

Breaking the Bond

This process is known as oxidative cleavage. Imagine taking a pair of molecular scissors and cutting right through the carbon-carbon double bond of But-2-ene (${\text{CH}}_3-\text{CH}=\text{CH}-{\text{CH}}_3$).

Once the bond is cleaved, the molecule is split into two fragments. Because we are using a strong oxidizing agent, these fragments don't just stay as aldehydes. Each $=\text{CH}-\text{R}$ group is fully oxidized. The carbon atom that was part of the double bond gains oxygen atoms until it reaches its highest stable oxidation state under these conditions, which is a carboxylic acid group ($-\text{COOH}$).

Let's look at the specific structure of But-2-ene. It is a perfectly symmetrical molecule. When we cleave it down the middle, both halves are identical ${\text{CH}}_3-\text{CH}=$ fragments.

Upon oxidation, each of these fragments transforms into acetic acid (${\text{CH}}_3\text{COOH}$). Therefore, the reaction yields exactly two molecules of acetic acid.

The final acidification step (${\text{H}}_3{\text{O}}^{+}$) is necessary because the reaction initially takes place in an alkaline medium, which would leave the product as a carboxylate salt (like potassium acetate). Adding acid protonates the salt, giving us the final, neutral carboxylic acid product.