Manganate 2053015 215282480 2008-05-27T14:39:12Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. [[Image:Manganate.png|thumb|150px|Structure of manganate]] The '''manganate''' ion is MnO<sub>4</sub><sup>2−</sup> and a '''manganate''' is any compound that contains the MnO<sub>4</sub><sup>2−</sup> group. These salts, e.g. [[potassium manganate]], are the [[conjugate base]] of the hypothetical species manganic acid, H<sub>2</sub>MnO<sub>4</sub>. Manganate salts are intermediates in the industrial synthesis of [[potassium permanganate]]. Occasionally [[permanganate]] and manganate salts are confused, but they behave quite differently. ==Structure== MnO<sub>4</sub><sup>2−</sup> is tetrahedral, being structurally related to other tetrahedral oxides such permanganate and osmium tetroxide. Salts of MnO<sub>4</sub><sup>2−</sup>, [[sulfate|SO<sub>4</sub><sup>2−</sup>]], and [[chromate|CrO<sub>4</sub><sup>2−</sup>]] are usually isostructural or nearly so, which means that they form solid solutions and have similar solubilities. Unlike sulfate and chromate, however, MnO<sub>4</sub><sup>2−</sup> is [[paramagnetic]]. ==Synthesis== ''See'' [[potassium manganate]] Manganate ion is stable in water only under strongly basic conditions. Consequently, salts are found with [[electropositive]] metals, such as Na<sup>+</sup>, K<sup>+</sup>, and Ba<sup>2+</sup> that do not form insoluble hydroxides. Manganates can be prepared by oxidation of MnO<sub>2</sub> or by reduction of permanganate. Note that O<sub>2</sub> is insufficiently oxidizing to further convert Mn(VI) to Mn(VII). Thus, the Mn(VI)/Mn(VII) oxidation is effected using stronger oxidants including [[Ozone|O<sub>3</sub>]] or Cl<sub>2</sub>. ==Reactions== MnO<sub>4</sub><sup>2−</sup> is the conjugate base of the hypothetical manganic acid, H<sub>2</sub>MnO<sub>4</sub>, which is too unstable to be isolated. The half-deprotonated acid has, however, been examined. Thus, the pK<sub>a</sub> of HMnO<sub>4</sub><sup>−</sup> has been determined as 7.1. MnO<sub>4</sub><sup>2−</sup> is about 100 times more basic than the acetate ion.{{ref|rush}} At lower pH's, the manganate ion will [[disproportionate]] to [[permanganate]] ion and [[manganese dioxide]]: ==Permanganate, manganate, hypomanganate, and manganite== The above reactions illustrate the close chemical relationship between the two principal soluble manganese oxides, permanganate and manganate. Two other, rarer members of the series are known. Hypomanganate, MnO<sub>4</sub><sup>3−</sup>, is a blue-colored ion of Mn(V) that forms when MnO<sub>4</sub><sup>2−</sup> is treated with manganite MnO<sub>4</sub><sup>4−</sup> at pH>12. It has also been generated by treatment of KMnO<sub>4</sub> in 10M KOH with H<sub>2</sub>O<sub>2</sub>. The pK<sub>a</sub> of HMnO<sub>4</sub><sup>2−</sup> is 13.7,{{ref|rush}} which indicates that solutions of hypomanganate contain significant amounts of the protonated form even at high pH's. Oxidations of alkenes by permanganate are proposed to proceed via the intermediacy of "esters" of hypomanganate, that is, species of the type MnO<sub>2</sub>(OR)<sub>2</sub><sup>−</sup> where R is an alkyl group.{{ref|Lee}} The brown-colored manganite ion, a Mn(IV) species, in turn is produced by dissolving its parent acid anhydride MnO<sub>2</sub> in strong alkali. Alternatively, MnO<sub>4</sub><sup>4−</sup> can be generated by reduction of MnO<sub>4</sub><sup>3−</sup>. ==Uses== BaMnO<sub>4</sub> and K<sub>2</sub>MnO<sub>4</sub> are used to oxidize primary and secondary alcohols. Primary alcohols are oxidised to aldehydes, then carboxylic acids. Secondary alcohols are oxidised to ketones. Tertiary alcohols cannot be oxidised in this way. Its use is similar to that for the Jones reagent. ==Literature cited== #{{note|nyholm}}{{cite journal | author = [[Ronald Sydney Nyholm|Nyholm]] R.S. Woolliams P.R. | title = "Manganates(VI)" | journal = Inorganic Syntheses | volume = XI| year = 1986 | pages = 56–61 }} #{{note|lee}}{{cite journal | author = Lee D.G. Chen T. | title = Reduction of Manganate(VI) by Mandelic Acid and Its Significance to Development of a General Mechanism for Oxidation of Organic Compounds by High-Valent Transition Metal Oxides| journal = Journal of the American Chemical Society| volume = 115| year = 1993 | pages = 11231–11236 | doi = 10.1021/ja00077a023}} #{{note|rush}}{{cite journal | author = Rush J.D. Bielski B.H. | title = Studies of Manganate(V), -(VI), and -(VII) Tetraoxyanions by Pulse Radiolysis. Optical Spectra of Protonated Forms | journal = Inorg. Chem. | volume = 34| year = 1995 | pages = 5832–8 | doi = 10.1021/ic00127a022}} == Other references == *G. Procter, S. V. Ley, G. H. Castle “Barium Manganate” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289. *Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5. See [[:Category:Manganates|category]] for a list. ==External links== *[http://www.npi.gov.au/database/substance-info/profiles/52.html National Pollutant Inventory - Manganese and compounds Fact Sheet] [[Category:Oxoanions]] [[Category:Manganates]] [[ru:Манганаты]]