|CAS number||, (dihydrate)|
|Jmol-3D images||Image 1|
|Molar mass||119.94 g mol−1|
|Main hazards||Oxidant, Corrosive|
|Other cations||Potassium permanganate
|Related compounds||Pertechnetic acid
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
Permanganic acid is the inorganic compound with the formula HMnO4. This strong oxoacid has been isolated as its dihydrate. It is the conjugate acid of permanganate salts. It is the subject of few publications and its characterization as well as its uses are very limited.
Preparation and structure
- BaMn2O8 + H2SO4 → 2 HMnO4 + BaSO4
Permanganic acid has also been prepared through the reaction of hydrofluorosilicic acid with potassium permanganate, through electrolysis, and through hydrolysis 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.
- 2 HMnO4 + MnO2 → 3 MnO2 + H2O + 3/2 O2
Decomposition is accelerated by heat, light, and acids. Concentrated solutions decompose more rapidly than dilute.
- Olsen, J. C. (1900). Permanganic Acid by Electrolysys. Easton, PA: The Chemical Publishing Company.
- Black, Homer Van Valkenburg (1900). The permanganates of barium, strontium, and calcium.. Easton, PA. p. 6.
- Frigerio, Norman (October 1969). "Preparation and properties of crystalline permanganic acid". Journal of the American Chemical Society. doi:10.1021/ja01050a058.
- Byers, Horace Greeley (1899). A Study of the Reduction of Permanganic acid by Manganese Dioxide.
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