Potassium manganate

Potassium manganate is the inorganic compound with the formula K₂MnO₄. This green-colored salt is an intermediate in the industrial synthesis of potassium permanganate (KMnO₄), a common chemical. Occasionally, potassium manganate and potassium permanganate are confused, but they are different compounds with distinctly different properties.

Structure

K₂MnO₄ is a salt, consisting of K⁺ cations and MnO₄²⁻ anions. X-ray crystallography shows that the anion is tetrahedral, with Mn-O distances of 1.66 Å, ca. 0.03 Å longer than the Mn-O distances in KMnO₄. It is isostructural with potassium sulfate.

Synthesis

The industrial route entails treatment of MnO₂ with air:

2 MnO₂ + 4 KOH + O₂ → 2 K₂MnO₄ + 2 H₂O

The transformation gives a green-colored melt. In fact, one can test an unknown substance for the presence of manganese by heating the sample in strong KOH in air. The production of a green coloration indicates the presence of Mn. This green color results from an intense absorption at 610 nm.

In laboratory, K₂MnO₄ can be synthesized by heating a...
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