View source for Manganese dioxide

{{Chembox new
|   Name = Manganese(IV) oxide
|   ImageFile = Manganese(IV) oxide.jpg
|   ImageSize = 200px
|   ImageName = Manganese(IV) oxide
|   IUPACName = Manganese dioxide<br />Manganese(IV) oxide
|   OtherNames = [[Pyrolusite]]
| Section1 = {{Chembox Identifiers
|   CASNo = 1313-13-9
  }}
| Section2 = {{Chembox Properties
|   Formula = MnO<sub>2</sub>
|   MolarMass = 86.9368 g/mol (''varies'')
|   Appearance = black solid
|   Density = 5.026 g/cm<sup>3</sup>, solid
|   Solubility = Insoluble
|   MeltingPt = 535 °C ''decomp.''
  }}
| Section4 = {{Chembox Thermochemistry
|   DeltaHf = &minus;520.9 kJ/mol
|   Entropy = 53.1 J.K<sup>&minus;1</sup>.mol<sup>&minus;1</sup>
  }}
| Section7 = {{Chembox Hazards
|   EUClass = Harmful ('''Xn''')
|   RPhrases = R20/22
|   SPhrases = S2, S25
|   NFPA-H =
|   NFPA-F =
|   NFPA-R = 2
|   NFPA-O = OX
  }}
| Section8 = {{Chembox Related
|   OtherAnions = [[Manganese disulfide]]
|   OtherCations = [[Technetium dioxide]]<br />[[Rhenium dioxide]]
|   OtherCpds = [[Manganese(II) oxide]]<br />[[Hausmannite]]<br />[[Manganese(III) oxide]]<br />[[Manganese trioxide]]<br />[[Manganese heptoxide]]
}}
}}
{{SI}}


==Overview==
'''Manganese(IV) oxide''' is the [[chemical compound]] MnO<sub>2</sub>, commonly called '''manganese dioxide'''. This blackish or brown solid occurs naturally as the mineral [[pyrolusite]], which is the main ore of [[manganese]]. It is also present in [[manganese nodule]]s. The principal use for MnO<sub>2</sub> is for dry-cell [[battery (electricity)|batteries]], such as the [[alkaline battery]] and the [[zinc-carbon battery]]. In 1976 this application accounted for 500,000 [[tonne]]s of pyrolusite.<sup>[1]</sup> MnO<sub>2</sub> is also used for production of [[Potassium permanganate|MnO<sub>4</sub><sup>–</sup>]].  It is used extensively as an [[redox|oxidising agent]] in [[organic synthesis]], for example, for the oxidation of [[allylic]] [[alcohol]]s.

==MnO<sub>2</sub> in organic synthesis==
Manganese dioxide is used as an oxidant in organic synthesis. The effectiveness of the reagent depends on the method of preparation, a problem that is typical for other heterogeneous reagents where surface area, among other variables, is a significant.<ref>Attenburrow, J.; Cameron, A. F. B.; Chapman, J. H.; Evans, R. M.; Hems, B. A.; Jansen, A. B. A.; Walker, T. J. Chem. Soc. 1952, 1094.</ref> The mineral pyrolusite makes a poor reagent. Usually, however, the reagent is generated by treatment of an aqueous solution KMnO<sub>4</sub> with a Mn(II) salt, typically the sulfate at various pH’s.

The predominant application of MnO<sub>2</sub> is for the oxidation of allylic alcohols to the corresponding aldehydes:
::cis-RCH=CHCH<sub>2</sub>OH + MnO<sub>2</sub> → cis-RCH=CHCHO + “MnO” + H<sub>2</sub>O
The configuration of the double bond is conserved in the reaction. The corresponding acetylenic alcohols are also suitable substrates, although the resulting propargylic aldehydes can be quite reactive. Benzylic and even unactivated alcohols are also good substrates. 1,2-Diols are cleaved by MnO<sub>2</sub> to dialdehydes or diketones. Otherwise, the applications of MnO<sub>2</sub> are numerous, being applicable to many kinds of reactions including amine oxidation, aromatization, oxidative coupling, and thiol oxidation.

==Miscellaneous==
MnO<sub>2</sub> has found many applications and investigations inside and beyond the laboratory. The examples below illustrate some:
*MnO<sub>2</sub> is used as a [[catalyst]] in the laboratory preparation of [[oxygen]] from [[potassium chlorate]], a classical experiment of elementary chemistry classes. The procedure consists of heating a mixture potassium chlorate and manganese dioxide in a hard glass container and collecting the gas over water. Manganese dioxide also catalyses the decomposition of [[hydrogen peroxide]] to oxygen and [[water]].
:2 H<sub>2</sub>O<sub>2</sub>([[aqueous|aq]]) → O<sub>2</sub>([[gas|g]]) + 2 H<sub>2</sub>O([[liquid|l]])
*Eighteenth-century British chemists referred to MnO<sub>2</sub> simply as ''manganese''. Elemental manganese was known as ''regulus of manganese''.
*Ancient [[Cave painting|cave painters]] used MnO<sub>2</sub> as a black or brown pigment.
*The MnO<sub>2</sub> was used for production of [[chlorine]] in the eighteenth century, before being displaced by eletrolytic methods. Manganese was recovered from such production by the so-called [[Weldon process]].
*Earliest glassmakers used manganese to remove the natural bluish-green tint of glass or to add a pinkish or purplish color.

==Other oxides of manganese==
The green salt [[potassium manganate]] is obtained in minutes when a solution of MnO<sub>2</sub> in molten KOH or NaOH is treated with [[oxidizing agent]]s such as [[potassium nitrate]] [[Potassium|K]][[Nitrogen|N]]O<sub>3</sub>), [[potassium perchlorate]] (K[[Chlorine|Cl]]O<sub>4</sub>), or even oxygen gas:
:2 MnO<sub>2</sub> + 4 OH<sup>–</sup> + O<sub>2</sub> → 2 MnO<sub>4</sub><sup>2–</sup> + 2 H<sub>2</sub>O

Potassium manganate converts into purple [[potassium permanganate]] in [[aqueous]] [[acid]]ic solution:
3 MnO<sub>4</sub><sup>2–</sup> + 4 H<sup>+</sup> → 2 MnO<sub>4</sub><sup>–</sup> + MnO<sub>2</sub>(s) + 2 H<sub>2</sub>O

==References==
# {{cite book | author=Greenwood, N. N.; & Earnshaw, A. |
title=Chemistry of the Elements (2nd Edn.) |
location=Oxford | publisher=Butterworth-Heinemann | year=1997 | id=ISBN 0-7506-3365-4}}
# Oosterhoeks Encyclopedie (Dutch)

==Further reading==
* Cahiez, G.; Alami, M.; Taylor, R. J. K.; Reid, M.; Foot, J. S. "Manganese Dioxide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.

==External links==
* [http://www.orgsyn.org/orgsyn/chemname.asp?nameID=33430 Index of Organic Synthesis procedures utilizing MnO<sub>2</sub>]
* [http://www.npi.gov.au/database/substance-info/profiles/52.html National Pollutant Inventory - Manganese and compounds Fact Sheet]
* [http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=14801 PubChem summary of MnO<sub>2</sub>]
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0175.htm International Chemical Safety Card 0175]

[[Category:Manganese compounds]]
[[Category:Oxides]]
[[Category:Oxidizing agents]]

[[de:Mangandioxid]]
[[fr:Dioxyde de manganèse]]
[[it:Diossido di manganese]]
[[nl:Mangaandioxide]]
[[ja:二酸化マンガン]]
[[pl:Tlenek manganu(IV)]]
[[sl:Manganov oksid]]
[[fi:Mangaanidioksidi]]
[[sv:Mangandioxid]]
[[zh:二氧化锰]]

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