View source for Permanganic acid

{{chembox
| Name = Permanganic acid
| ImageFile = Permanganic-acid-3D-balls.png
| ImageSize = 100px
| ImageName = Permanganic acid
| OtherNames = Hydroxy(trioxo)manganese<br />Hydrogen permanganate
|Section1={{Chembox Identifiers
| ChemSpiderID = 374116
| InChI = 1S/Mn.H2O.3O/h;1H2;;;/q+1;;;;/p-1
| SMILES = O=[Mn](=O)(=O)O
| InChIKey = ZJBYBXHCMWGGRR-UHFFFAOYSA-M
| CASNo = 13465-41-3
| CASNo_Comment =
| CASNo1 = 24653-70-1
| CASNo1_Comment = (dihydrate)
| PubChem = 422689
| EINECS = 236-695-4
  }}
|Section2={{Chembox Properties
| Formula = HMnO<sub>4</sub>
| MolarMass = 119.94 g mol<sup>−1</sup>
| Appearance = violet
| Density = 
| Solubility =
| pKa =
  }}
|Section3={{Chembox Structure
| MolShape = 
| Dipole =
  }}
|Section7={{Chembox Hazards
| ExternalSDS =
| MainHazards = Oxidant, Corrosive
| NFPA-H = 
| NFPA-F = 
| NFPA-R = 
| NFPA-S = 
}}
|Section8={{Chembox Related
| OtherAnions = 
| OtherCations = [[Potassium permanganate]]<br />[[Sodium permanganate]]<br />[[Calcium permanganate]]
| OtherCompounds = [[Pertechnetic acid]]<br>[[Perrhenic acid]]<br>[[Perchloric acid]]
  }}
}}

'''Permanganic acid''' is the [[inorganic compound]] with the formula  [[Proton|H]][[Manganate|MnO<sub>4</sub>]].  This [[strong acid|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==
Permanganic acid is most often prepared by the reaction of dilute [[sulfuric acid]] with a solution of [[barium permanganate]], the insoluble [[barium sulfate]] byproduct being removed by filtering:<ref name=electro1>{{cite book|last=Olsen|first=J. C.|title=Permanganic Acid by Electrolysys|year=1900|publisher=The Chemical Publishing Company|location=Easton, PA|url=http://books.google.com/books?id=EJNPAAAAYAAJ&printsec=frontcover#v=onepage&q&f=false}}</ref>
:Ba(MnO<sub>4</sub>)<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → 2 HMnO<sub>4</sub> + BaSO<sub>4</sub>
The sulfuric acid used must be dilute; reactions of permanganates with concentrated sulfuric acid yield the [[anhydride]], [[manganese heptoxide]].

Permanganic acid has also been prepared through the reaction of [[hydrofluorosilicic acid]] with [[potassium permanganate]],<ref name=bsc>{{cite book|last=Black|first=Homer Van Valkenburg|title=The permanganates of barium, strontium, and calcium.|year=1900|location=Easton, PA|page=6|url=http://books.google.com/books?id=HZNPAAAAYAAJ&printsec=frontcover#v=onepage&q&f=false}}</ref> through [[electrolysis]],<ref name=electro1 /> and through [[hydrolysis]] of manganese heptoxide, though the last route often results in explosions.<ref name=electro1 />

Crystalline permanganic acid has been prepared at low temperatures as the dihydrate, HMnO<sub>4</sub>·2H<sub>2</sub>O.<ref name=ACS1>{{cite journal|last=Frigerio|first=Norman|title=Preparation and properties of crystalline permanganic acid|journal=Journal of the American Chemical Society|date=October 1969|url=http://pubs.acs.org/doi/abs/10.1021/ja01050a058|doi=10.1021/ja01050a058}}</ref>

Although its structure has not been verified spectroscopically or crystallographically, HMnO<sub>4</sub> is assumed to be adopt a tetrahedral structure akin to that for [[perchloric acid]].

==Reactions==
As a strong acid<!--pKa???-->, HMnO<sub>4</sub> is deprotonated to form the intensely purple coloured [[permanganate]]s.  [[Potassium permanganate]], KMnO<sub>4</sub>, is a widely used, versatile and powerful oxidising agent.

Permanganic acid solutions are unstable, and gradually decompose into [[manganese dioxide]], oxygen, and water, with initially formed manganese dioxide catalyzing further decomposition.<ref name=MnO2>{{cite book|last=Byers|first=Horace Greeley|title=A Study of the Reduction of Permanganic acid by Manganese Dioxide|year=1899|url=http://books.google.com/books?id=U5xPAAAAYAAJ&printsec=frontcover#v=onepage&q&f=false}}</ref> 
:2 HMnO<sub>4</sub> + MnO<sub>2</sub> → 3 MnO<sub>2</sub> + H<sub>2</sub>O + 3/2 O<sub>2</sub>
Decomposition is accelerated by heat, light, and acids.  Concentrated solutions decompose more rapidly than dilute.{{r|MnO2}}

==References==
{{reflist}}
{{Manganese compounds}}
{{Hydrogen compounds}}

[[Category:Hydrogen compounds]]
[[Category:Manganese compounds]]
[[Category:Oxidizing agents]]
[[Category:Oxidizing acids]]
[[Category:Mineral acids]]


{{Inorganic-compound-stub}}