Oxidative cleavage of alkenes with KMnO4

Steps:

• Retinol in vitamin A has C=C bonds in a polyene chain, requiring cleavage and further oxidation.
• Acidified KMnO4 cleaves C=C under hot, concentrated conditions, unlike cold, dilute which forms diols.
• Cleavage oxidizes =CH-R to R-COOH and =CR1R2 to R1R2C=O, with aldehydes further oxidized to carboxylic acids.
• Retinol's structure yields ketone from the ionone ring and carboxylic acids from chain fragments.

Why D is correct:

• Hot, concentrated acidified KMnO4 fully cleaves alkenes and oxidizes aldehydic products to carboxylic acids, while ketonic fragments remain ketones, matching retinol's outcomes.

Why the others are wrong:

• A: Cold, dilute conditions dihydroxylate without breaking C=C bonds.
• B: Cold, dilute does not cleave to ketones or acids.
• C: Hot, concentrated oxidizes beyond aldehydes to carboxylic acids.

Final answer: D