Magnesium Permanganate, Mg(MnO₄)₂

Michael and Garner describe Mg(MnO₄)₂ as a crystalline salt with a bluish-grey metallic lustre which desiccation in vacuo at 100° C. alters to a purple tint. Mitscherlich and Aschoff originally described it as a deliquescent substance with 6 molecules of water of crystallisation. Mitscherlich's original method of preparation, reaction between solutions of barium permanganate and magnesium sulphate, is still the best.

In aqueous solution magnesium permanganate is rapidly decomposed at water-bath heat, giving off oxygen and ozone. It is apparently liable to explode in the solid condition.

Magnesium permanganate is a very vigorous oxidising agent. This vigour may be partly connected with the tendency of magnesium salts to hydrolyse to magnesium hydroxide. Since strong alkali is produced when potassium permanganate oxidises substances in aqueous solution, magnesium permanganate is often a preferable oxidising agent, apart from its vigour, because it only involves the formation of the relatively inert magnesium hydroxide.

A solution of the salt in glacial acetic acid is an extremely powerful oxidising agent; in pyridine its oxidising powers are much less.