A permanganate () is a chemical compound containing the manganate(VII) ion, MnO⁻
₄, the conjugate base of permanganic acid. Because the manganese atom is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent. The ion is a transition metal oxo complex with tetrahedral geometry. Permanganate solutions are purple in color and are stable in neutral or slightly alkaline media. The exact chemical reaction is dependent upon the organic contaminants present and the oxidant utilized. For example, trichloroethane (C₂H₃Cl₃) is oxidized by permanganate ions to form carbon dioxide (CO₂), manganese dioxide (MnO₂), hydrogen ions (H⁺), and chloride ions (Cl⁻).

8MnO⁻
₄ + 3C
₂H
₃Cl
₃ → 6CO
₂ + 8MnO
₂ + H⁺
+ 4H
₂O + 9Cl⁻

In an acidic solution, permanganate(VII) is reduced to the pale pink +2 oxidation state of the manganese(II) (Mn²⁺) ion.

8 H⁺
+ MnO⁻
₄ + 5 e⁻ → Mn²⁺ + 4 H₂O

In a strongly basic solution, permanganate(VII) is reduced to the green +6 oxidation state of the manganate ion, MnO²⁻
₄.

MnO⁻
₄ + e⁻ → MnO²⁻
₄

In a neutral medium, however, it gets reduced to the brown +4 oxidation state of manganese dioxide MnO₂.

2 H₂O + MnO⁻
₄ + 3 e⁻ → MnO₂ + 4 OH⁻