Write the balanced equation for the oxidation of 2‑pentanol (CH₃CH₂CH(OH)CH₂CH₃) to 2‑pentanone (CH₃CH₂COCH₂CH₃) using potassium permanganate in alkaline medium. State the number of electrons transferred per mole of 2‑pentanol.
Answer
Balanced equation: 3 CH₃CH₂CH(OH)CH₂CH₃ + 2 KMnO₄ + 6 OH⁻ → 3 CH₃CH₂COCH₂CH₃ + 2 MnO₂ + 6 H₂O. Electrons transferred per mole of 2‑pentanol = 2.
Step-by-step solution
- Identify the oxidation: secondary alcohol → ketone; each mole of alcohol donates 2 electrons.
- Know that MnO₄⁻ in alkaline medium is reduced to MnO₂, accepting 3 electrons per MnO₄⁻.
- To balance electrons, use 2 KMnO₄ (providing 6 e⁻) with 3 moles of alcohol (providing 6 e⁻).
- Write the skeletal reaction: 3 R‑CH(OH)‑R' + 2 KMnO₄ + 6 OH⁻ → 3 R‑CO‑R' + 2 MnO₂ + 6 H₂O.
- Ensure all atoms and charges are balanced: C:3→3, H:… etc. The equation satisfies mass and charge balance.
- Thus the balanced equation is as given and the electron count per mole of alcohol is 2.
Common mistake: Miscalculating electron transfer or using wrong stoichiometry
Concept tested: oxidation of secondary alcohols with KMnO₄
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