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Potassium permanganate is among the most important transition metal compounds for both JEE and practical chemistry.

Preparation: MnO2 (pyrolusite) fused with KOH and air gives K2MnO4 (green manganate, Mn^6+). Electrolytic or disproportionation oxidation converts it to KMnO4 (purple, Mn^7+).

Structure: MnO4^- is tetrahedral. The deep purple colour arises from LMCT (O^2- to Mn^7+) since Mn^7+ is d^0. The colour is NOT from d-d transitions.

Oxidising reactions by medium:

• Acidic: MnO4^- + 8H^+ + 5e^- to Mn^2+ + 4H2O. n-factor = 5. Purple to colourless.
• Neutral: MnO4^- + 2H2O + 3e^- to MnO2 + 4OH^-. n-factor = 3. Purple to brown precipitate.
• Strongly alkaline: MnO4^- + e^- to MnO4^2-. n-factor = 1. Purple to green.

Self-indicator: The purple colour itself signals the endpoint in titrations — no external indicator needed.

Key reactions: With oxalic acid (2:5 ratio, autocatalytic at 60-70 degrees C), with FeSO4 (1:5 ratio), with HCl (produces Cl2 — avoid HCl in permanganate titrations). Baeyer's test uses cold dilute KMnO4 for unsaturation detection.

Practical note: KMnO4 is NOT a primary standard (slowly decomposes). It must be standardised against a primary standard like sodium oxalate.