devarshi-dt-logo

Question:

But-2-ene on reaction with alkaline KMnO4 at elevated temperature followed by acidification will give:

2 molecules of CH3CHO

2 molecules of CH3COOH

one molecule of CH3CHO and one molecule of CH3COOH

CH3−CH|OH−CH|OH−CH3

Solution:

The reaction of But-2-ene with alkaline KMnO4 at elevated temperature followed by acidification is an example of oxidative cleavage of alkenes. The double bond in But-2-ene breaks, and each carbon atom that was part of the double bond gets oxidized. The products depend on the substitution pattern of the alkene. In this case, But-2-ene is a symmetrical alkene, so the oxidative cleavage will yield two molecules of the same product.

The reaction proceeds as follows:

CH3CH=CHCH3 + KMnO4 (alkaline, heat) → CH3CH(OH)CH(OH)CH3 (intermediate)

CH3CH(OH)CH(OH)CH3 + H+ (acidification) → 2CH3CHO

The intermediate is a vicinal diol, which is further oxidized under acidic conditions to form two molecules of acetaldehyde (CH3CHO).

Therefore, the correct answer is 2 molecules of CH3CHO.