Oxidation of an aldehyde with acidified potassium permanganate gives
- A. a primary alcohol
- B. a ketone
- C. a carboxylic acid with the same number of carbon atoms
- D. carbon dioxide only
Explanation
The hydrogen on the carbonyl carbon is replaced by a hydroxyl group, so ethanal becomes ethanoic acid with no change in the length of the chain. This ready oxidation is why aldehydes act as reducing agents and give positive results with Tollens and Fehling's reagents. Ketones cannot be oxidised in this way without breaking the carbon skeleton.
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