Potassium permanganate (KMnO₄) is a strong oxidizing agent. When it reacts with ethanol (C₂H₅OH), it oxidizes it first to ethanal (acetaldehyde, CH₃CHO) and then further to ethanoic acid (acetic acid, CH₃COOH). In acidic conditions, the oxidation goes all the way to acetic acid. This reaction is important in Class 10 and Class 12 Chemistry.
KMnO₄ oxidizes ethanol (C₂H₅OH) → ethanoic acid (acetic acid, CH₃COOH) in acidic medium.
Oxidation occurs in two steps: ethanol → ethanal → ethanoic acid.
KMnO₄ is purple/violet; it decolorizes on oxidizing ethanol (reduced to Mn²⁺).
K₂Cr₂O₇/H₂SO₄ also oxidizes ethanol to acetic acid.
PCC oxidizes primary alcohol only to aldehyde (stops at ethanal stage).
Tertiary alcohols are not oxidized by KMnO₄ under normal conditions.
Step 1 — Ethanol → Ethanal (Acetaldehyde): C₂H₅OH → [O] → CH₃CHO (Primary alcohol → Aldehyde)
Step 2 — Ethanal → Ethanoic Acid (Acetic Acid): CH₃CHO → [O] → CH₃COOH (Aldehyde → Carboxylic acid)
Overall reaction: C₂H₅OH → [KMnO₄/H⁺] → CH₃COOH Ethanol → Acetic acid (Ethanoic acid)
So, potassium permanganate oxidizes ethanol to acetic acid (ethanoic acid).
The product depends on the oxidizing conditions:
Acidic KMnO₄ (KMnO₄/H₂SO₄ or KMnO₄/HCl): • Strongly oxidizing conditions • Primary alcohols → Carboxylic acids (all the way) • Ethanol → Ethanoic acid (acetic acid)
Neutral/Alkaline KMnO₄: • Milder conditions • Can give complete oxidation to CO₂ and H₂O
Other oxidizing agents: • K₂Cr₂O₇ / H₂SO₄ (acidified dichromate): also oxidizes ethanol to acetic acid • PCC (Pyridinium chlorochromate): oxidizes primary alcohol to aldehyde only (stops at ethanal)
Key observation: • KMnO₄ solution is purple/violet in colour • After oxidizing ethanol, the colour decolorizes (turns colourless) • This decolorization is evidence of oxidation • KMnO₄ is reduced from Mn⁷⁺ to Mn²⁺ (colourless manganese ions in acidic medium) or Mn⁴⁺ (brown MnO₂ in neutral medium)
This colour change is used as a test for the presence of reducing agents (alcohols, aldehydes).
Type of alcohol | With strong oxidant (KMnO₄/H⁺) | With mild oxidant (PCC) Primary (e.g., ethanol) | Aldehyde → Carboxylic acid | Aldehyde only Secondary (e.g., propan-2-ol) | Ketone | Ketone Tertiary (e.g., tert-butanol) | No reaction (no α-H on correct side) | No reaction
Ethanol is a primary alcohol, so it is oxidized all the way to acetic acid by KMnO₄.
Potassium permanganate (KMnO₄), especially in acidic medium, oxidizes ethanol (C₂H₅OH) to ethanoic acid (acetic acid, CH₃COOH). The oxidation occurs stepwise: ethanol → ethanal (acetaldehyde) → ethanoic acid.
KMnO₄ is purple/violet in colour. When it oxidizes ethanol, the purple colour decolorizes (becomes colourless in acidic medium) as Mn⁷⁺ is reduced to Mn²⁺. This colour change indicates a positive test for reducing agents.
KMnO₄ (strong oxidant): oxidizes primary alcohols all the way to carboxylic acids (ethanol → acetic acid). PCC (mild oxidant): oxidizes primary alcohols only to aldehydes (ethanol → ethanal/acetaldehyde) — stops at aldehyde stage.
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