Permanganic acid (or manganic(VII) acid) is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula H MnO₄. This strong

oxoacid An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...

has been isolated as its dihydrate. It is the

conjugate acid A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

permanganate A permanganate () is a chemical compound containing the manganate(VII) ion, , 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 tra ...

salts. It is the subject of few publications and its characterization as well as its uses are very limited.

Preparation and structure

Permanganic acid is most often prepared by the reaction of dilute

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

with a solution of barium permanganate, the insoluble

barium sulfate Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium an ...

byproduct being removed by filtering: :Ba(MnO₄)₂ + H₂SO₄ → 2 HMnO₄ + BaSO₄↓ The sulfuric acid used must be dilute; reactions of permanganates with concentrated sulfuric acid yield the

anhydride An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...

, manganese heptoxide. Permanganic acid has also been prepared through the reaction of hydrofluorosilicic acid with

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

, through

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...

, and through

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of manganese heptoxide, though the last route often results in explosions. Crystalline permanganic acid has been prepared at low temperatures as the dihydrate, HMnO₄·2H₂O. Although its structure has not been verified spectroscopically or crystallographically, HMnO₄ is assumed to be adopt a tetrahedral structure akin to that for

perchloric acid Perchloric acid is a mineral acid with the formula H Cl O4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous sol ...

Reactions

As a strong acid, HMnO₄ is deprotonated to form the intensely purple coloured

Potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

, KMnO₄, is a widely used, versatile and powerful oxidising agent. Permanganic acid solutions are unstable, and gradually decompose into

manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cell ...

, oxygen, and water, with initially formed manganese dioxide catalyzing further decomposition. Decomposition is accelerated by heat, light, and acids. Concentrated solutions decompose more rapidly than dilute.

References

{{Hydrogen compounds Hydrogen compounds Manganese(VII) compounds Oxidizing agents Oxidizing acids Mineral acids Transition metal oxoacids