Difference between revisions of "Manganese dioxide"

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|  OtherNames = [[Pyrolusite]]<br/>Manganese(IV) oxide
 
|  OtherNames = [[Pyrolusite]]<br/>Manganese(IV) oxide
 
| Section1 = {{Chembox Identifiers
 
| Section1 = {{Chembox Identifiers
 +
|  InChI = 1/Mn.2O/rMnO2/c2-1-3
 +
|  StdInChI = 1S/Mn.2O
 +
|  InChIKey = NUJOXMJBOLGQSY-MQJJFXMEAL
 +
|  StdInChIKey = NUJOXMJBOLGQSY-UHFFFAOYSA-N
 
|  CASNo = 1313-13-9
 
|  CASNo = 1313-13-9
 
|    CASNo_Ref = {{cascite}}
 
|    CASNo_Ref = {{cascite}}
 +
|  EC-number = 215-202-6
 +
|  ChemSpiderID =
 
|  PubChem = 14801
 
|  PubChem = 14801
−
|  EINECS = 215-202-6
 
 
|  RTECS = OP0350000
 
|  RTECS = OP0350000
−
|  InChI = 1/Mn.2O
 
−
|  StdInChI = 1S/Mn.2O
 
−
|  StdInChIKey = NUJOXMJBOLGQSY-UHFFFAOYSA-N
 
 
   }}
 
   }}
 
| Section2 = {{Chembox Properties
 
| Section2 = {{Chembox Properties
−
|  Reference = <ref>{{RubberBible62nd|page=B-118}}</ref>
+
|  Reference = <ref>{{RubberBible62nd|page=B-118}}.</ref>
 
|  Formula = MnO<sub>2</sub>
 
|  Formula = MnO<sub>2</sub>
 
|  MolarMass = 86.937 g/mol
 
|  MolarMass = 86.937 g/mol
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   }}
 
   }}
 
| Section4 = {{Chembox Thermochemistry
 
| Section4 = {{Chembox Thermochemistry
−
|  Reference = <ref>{{Jolly2nd|page=586}}</ref>
+
|  Reference = <ref>{{Jolly2nd|page=586}}.</ref>
 
|  DeltaHf = −519.5 kJ/mol
 
|  DeltaHf = −519.5 kJ/mol
 
|  Entropy = 53.0 J&thinsp;K<sup>−1</sup>&thinsp;mol<sup>−1</sup>
 
|  Entropy = 53.0 J&thinsp;K<sup>−1</sup>&thinsp;mol<sup>−1</sup>
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| Section7 = {{Chembox Hazards
 
| Section7 = {{Chembox Hazards
 
|  Reference = <ref>{{CLP Regulation|index=025-001-00-3|page=420}}</ref>
 
|  Reference = <ref>{{CLP Regulation|index=025-001-00-3|page=420}}</ref>
−
|  ExternalMSDS = [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0175.htm ICSC 0175]
+
|  ExternalMSDS = {{ICSC-small|01|75}}
 
|  EUIndex = 025-001-00-3
 
|  EUIndex = 025-001-00-3
−
|  GHSPictograms = {{GHS07}}
+
|  GHSPictograms = {{GHS07|Acute Tox. (oral, inhal.) 4}}
 
|  GHSSignalWord = WARNING
 
|  GHSSignalWord = WARNING
−
|  HPhrases = H332, H302
+
|  HPhrases = {{H-phrases|302|332}}
−
|  PPhrases =  
+
|  PPhrases = {{P-phrases|264|270|261|271|301+312|330|304+340|501}}
 
|  FlashPt = non-flammable
 
|  FlashPt = non-flammable
 
   }}
 
   }}
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}}
 
}}
  
−
'''Manganese dioxide''' is the [[inorganic compound]] with the [[chemical formula|formula]] MnO<sub>2</sub>. 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]].<ref name="G&E">{{Greenwood&Earnshaw1st|pages=1218–20}}.</ref> In 1976 this application accounted for 500,000 [[tonne]]s of pyrolusite. 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|oxidizing agent]] in [[organic synthesis]], for example, for the oxidation of [[allylic]] [[alcohol]]s.
+
'''Manganese dioxide''' is the [[inorganic compound]] with the [[chemical formula|formula]] MnO<sub>2</sub>. 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]].<ref name="G&E">{{Greenwood&Earnshaw1st|pages=1218–20}}.</ref> In 1976 this application accounted for 500,000&nbsp;[[tonne]]s of pyrolusite. 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|oxidizing agent]] in [[organic synthesis]], for example, for the oxidation of [[allylic]] [[alcohol]]s.
  
 
==Structure==
 
==Structure==
 
[[File:Resinoid crystal of manganese dioxide.jpg|thumb|200px|left|a resinoid crystal of the manganese dioxide generated in the crack of the limestone of mud from [[Solnhofen]], [[Bayern]], [[Germany]].]]
 
[[File:Resinoid crystal of manganese dioxide.jpg|thumb|200px|left|a resinoid crystal of the manganese dioxide generated in the crack of the limestone of mud from [[Solnhofen]], [[Bayern]], [[Germany]].]]
−
A number of [[polymorphism (materials science)|polymorphs]] of MnO<sub>2</sub> have been identified. The most common is β-MnO<sub>2</sub>,([[pyrolusite]]) which has the [[titanium dioxide|TiO<sub>2</sub>]], rutile structure.<ref name=Wells>{{Wells5th}}.</ref> Others are  α-MnO<sub>2</sub>, γ-MnO<sub>2</sub>, ε-MnO<sub>2</sub>, and λ-MnO<sub>2</sub>.<ref name=Wells/><ref name=Fong>{{citation | last1 = Fong | first1 = G. C. | last2 = Kennedy | first2 = B. J. | last3= Elcombe | first3 = M. M. | title = A powder neutron diffraction study of λ- and γ-manganese dioxide and of LiMn<sub>2</sub>O<sub>4</sub> | journal = Z. Kristallogr. | yesr = 1994 | volume = 209 | issue = 12 | pages = 941–45}}.</ref> The structures of all of these forms are closely related and are built from linked MnO<sub>6</sub> octahedra and "tunnels" capable of holding cations are formed in all except β-MnO<sub>2</sub>.<ref name=Wells/><ref name=Fong/> Interest in these [[polymorphism (materials science)|polymorphs]] is due to their use in [[lithium ion]] batteries.
+
A number of [[polymorphism (materials science)|polymorphs]] of MnO<sub>2</sub> have been identified. The most common is β-MnO<sub>2</sub>,([[pyrolusite]]) which has the [[titanium dioxide|TiO<sub>2</sub>]], rutile structure.<ref name=Wells>{{Wells5th}}.</ref> Others are  α-MnO<sub>2</sub>, γ-MnO<sub>2</sub>, ε-MnO<sub>2</sub>, and λ-MnO<sub>2</sub>.<ref name=Wells/><ref name=Fong>{{citation | last1 = Fong | first1 = G. C. | last2 = Kennedy | first2 = B. J. | last3 = Elcombe | first3 = M. M. | title = A powder neutron diffraction study of λ- and γ-manganese dioxide and of LiMn<sub>2</sub>O<sub>4</sub> | journal = Z. Kristallogr. | year = 1994 | volume = 209 | issue = 12 | pages = 941–45}}.</ref> The structures of all of these forms are closely related and are built from linked MnO<sub>6</sub> octahedra and "tunnels" capable of holding cations are formed in all except β-MnO<sub>2</sub>.<ref name=Wells/><ref name=Fong/> Interest in these [[polymorphism|polymorphs]] is due to their use in [[lithium ion]] batteries.
  
 
==History and chemical reactions==
 
==History and chemical reactions==
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==Production==
 
==Production==
−
The natural occuring manganese dioxide contains impurities and a considerable amount of manganese(III) ions. Only a limited number of deposits contain the γ modification in high enough purity, which is the prefered material for the battery industry. The ferrite production also needs manganese dioxide with only small amounts of impurities. Therfore the production of synthetic manganese dioxide is important. Two groups of methods are used, yielding chemical manganese dioxide (CMD) and electrolytical manganese dioxide (EMD). The CMD is mostly used for the production of ferrites, while the EMD is used for the production of batteries.<ref name="ChiuZMnO2">{{citation | last = Preisler | first = Eberhard | title = Moderne Verfahren der Großchemie: Braunstein | journal = Chemie in unserer Zeit | year = 1980 | volume = 14 | pages = 137–48 | doi = 10.1002/ciuz.19800140502}}.</ref>
+
The natural occuring manganese dioxide contains impurities and a considerable amount of manganese(III) ions. Only a limited number of deposits contain the γ-modification in high enough purity, which is the prefered material for the battery industry. The ferrite production also needs manganese dioxide with only small amounts of impurities. Therfore the production of synthetic manganese dioxide is important. Two groups of methods are used, yielding chemical manganese dioxide (CMD) and electrolytical manganese dioxide (EMD). The CMD is mostly used for the production of ferrites, while the EMD is used for the production of batteries.<ref name="ChiuZMnO2">{{citation | last = Preisler | first = Eberhard | title = Moderne Verfahren der Großchemie: Braunstein | journal = Chemie in unserer Zeit | year = 1980 | volume = 14 | pages = 137–48 | doi = 10.1002/ciuz.19800140502}}.</ref>
  
 
===Chemical manganese dioxide===
 
===Chemical manganese dioxide===
−
 
 
One of the two chemical methods starts from natural manganese dioxide and converts it with [[dinitrogen tetroxide]] (N<sub>2</sub>O<sub>4</sub>) and water to manganese(II) nitrate solution, which is purified and after evaporation of the water a crystaline solid forms. At temperatures of 400&nbsp;°C the reverse reaction releases the N<sub>2</sub>O<sub>4</sub> and manganese dioxide is formed.<ref name="ChiuZMnO2"/>
 
One of the two chemical methods starts from natural manganese dioxide and converts it with [[dinitrogen tetroxide]] (N<sub>2</sub>O<sub>4</sub>) and water to manganese(II) nitrate solution, which is purified and after evaporation of the water a crystaline solid forms. At temperatures of 400&nbsp;°C the reverse reaction releases the N<sub>2</sub>O<sub>4</sub> and manganese dioxide is formed.<ref name="ChiuZMnO2"/>
−
 
 
:MnO<sub>2</sub> +  N<sub>2</sub>O<sub>4</sub>  → Mn(NO<sub>3</sub>)<sub>2</sub>
 
:MnO<sub>2</sub> +  N<sub>2</sub>O<sub>4</sub>  → Mn(NO<sub>3</sub>)<sub>2</sub>
 
:Mn(NO<sub>3</sub>)<sub>2</sub> →  MnO<sub>2</sub> +  N<sub>2</sub>O<sub>4</sub>
 
:Mn(NO<sub>3</sub>)<sub>2</sub> →  MnO<sub>2</sub> +  N<sub>2</sub>O<sub>4</sub>
  
 
In the other chemical process the natural manganeses dioxide ore is reduced with oil or coal to the managanese oxide. The [[manganese(II) oxide]] is dissolved in [[sulfuric acid]] and after purification the manganese(II) is precipitated as carbonate by adding [[ammonium carbonate]]. The carbonate is heated with air and a manganese oxide forms, which is a mixture between manganese(II) and manganese(IV) oxide. To complete the reaction the oxide is suspended in sulfuric acid and [[sodium chlorate]] is added. The [[chloric acid]] oxidizes the manganese oxide and chlorine is formed as by-product.<ref name="ChiuZMnO2"/>
 
In the other chemical process the natural manganeses dioxide ore is reduced with oil or coal to the managanese oxide. The [[manganese(II) oxide]] is dissolved in [[sulfuric acid]] and after purification the manganese(II) is precipitated as carbonate by adding [[ammonium carbonate]]. The carbonate is heated with air and a manganese oxide forms, which is a mixture between manganese(II) and manganese(IV) oxide. To complete the reaction the oxide is suspended in sulfuric acid and [[sodium chlorate]] is added. The [[chloric acid]] oxidizes the manganese oxide and chlorine is formed as by-product.<ref name="ChiuZMnO2"/>
−
 
 
:2MnO<sub>2</sub> +  C  →  2MnO + CO<sub>2</sub>
 
:2MnO<sub>2</sub> +  C  →  2MnO + CO<sub>2</sub>
 
:MnO + H<sub>2</sub>SO<sub>4</sub> →  MnSO<sub>4</sub> + H<sub>2</sub>O
 
:MnO + H<sub>2</sub>SO<sub>4</sub> →  MnSO<sub>4</sub> + H<sub>2</sub>O
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===Electrolytical manganese dioxide===
 
===Electrolytical manganese dioxide===
−
The electrochemical method starts from the manganese(II) sulfate solution, which is obtained by similar processes mentioned in the previous method, but some producers use hydrogen instead of coal and oil for the reduction. Iron is oxidized by addition of manganese dioxide and precipitates at a pH of 5 to 6, while other ions like cobalt, nickel and copper are precipitated as sulfides. [[Electrolysis]] is than used to oxidize the manganese. During that process the manganese dioxide forms a layer on the [[anode]], which is made from [[titanium]], [[lead]] or [[graphite]].<ref name="ChiuZMnO2"/>  
+
The electrochemical method starts from the manganese(II) sulfate solution, which is obtained by similar processes mentioned in the previous method, but some producers use hydrogen instead of coal and oil for the reduction. Iron is oxidized by addition of manganese dioxide and precipitates at a pH of 5 to 6, while other ions like cobalt, nickel and copper are precipitated as sulfides. [[Electrolysis]] is than used to oxidize the manganese. During that process the manganese dioxide forms a layer on the [[anode]], which is made from [[titanium]], [[lead]] or [[graphite]].<ref name="ChiuZMnO2"/>
−
   
+
  :MnO<sub>2</sub> +  H<sub>2</sub>  →  MnO + H<sub>2</sub>O
−
:MnO<sub>2</sub> +  H<sub>2</sub>  →  MnO + H<sub>2</sub>O
 
 
:MnO + H<sub>2</sub>SO<sub>4</sub>  →  MnSO<sub>4</sub> + H<sub>2</sub>O
 
:MnO + H<sub>2</sub>SO<sub>4</sub>  →  MnSO<sub>4</sub> + H<sub>2</sub>O
 
:Mn<sup>2+</sup> + H<sub>2</sub>O → MnO<sub>2</sub> + 2e<sup>−</sup> + 2H<sup>+</sup>
 
:Mn<sup>2+</sup> + H<sub>2</sub>O → MnO<sub>2</sub> + 2e<sup>−</sup> + 2H<sup>+</sup>
Line 99: Line 97:
  
 
===MnO<sub>2</sub> in organic synthesis===
 
===MnO<sub>2</sub> in organic synthesis===
−
A specialized use of manganese dioxide is as an oxidant in [[organic synthesis]].<ref>{{citation | last1 = Cahiez | first1 = G. | last2 = Alami | first2 = M. | last3 = Taylor | first3 = R. J. K. | last4 = Reid | first4 = M. | last5 = Foot | first5 = J. S. | contribution = Manganese Dioxide | title = Encyclopedia of Reagents for Organic Synthesis | editor-first = Leo A. | editor-last = Paquette | year = 2004 | publisher = J. Wiley & Sons | location = New York}}.</ref> 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 factor.<ref>{{citation | last1 = Attenburrow | first1 = J. | last2 = Cameron | first2 = A. F. B. | last3 = Chapman | first3 = J. H. | last4 = Evans | first4 = R. M. | last5 = Hems | first5 = B. A. | last6 = Jansen | first6 = A. B. A. | last7 = Walker | first7 = T. | journal = J. Chem. Soc. | year = 1952 | page = 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.  MnO<sub>2</sub> oxidizes allylic alcohols to the corresponding aldehydes:
+
A specialized use of manganese dioxide is as an oxidant in [[organic synthesis]].<ref>{{EROS | last1 = Cahiez | first1 = G. | last2 = Alami | first2 = M. | last3 = Taylor | first3 = R. J. K. | last4 = Reid | first4 = M. | last5 = Foot | first5 = J. S. | contribution = Manganese Dioxide}}.</ref> 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 factor.<ref>{{citation | last1 = Attenburrow | first1 = J. | last2 = Cameron | first2 = A. F. B. | last3 = Chapman | first3 = J. H. | last4 = Evans | first4 = R. M. | last5 = Hems | first5 = B. A. | last6 = Jansen | first6 = A. B. A. | last7 = Walker | first7 = T. | title = A synthesis of vitamin a from ''cyclo''hexanone | journal = J. Chem. Soc. | year = 1952 | page = 1094–11 | doi = 10.1039/JR9520001094}}.</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.  MnO<sub>2</sub> oxidizes 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
+
:''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.
 
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.
  
 
===Precursor to permanganate===
 
===Precursor to permanganate===
−
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.<ref name="Ullmann" />
+
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]] (KNO<sub>3</sub>), [[potassium perchlorate]] (KClO<sub>4</sub>), or even oxygen gas.<ref name="Ullmann" />
−
: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
+
:2MnO<sub>2</sub> + 4OH<sup>−</sup> + O<sub>2</sub> → 2MnO<sub>4</sub><sup>2−</sup> + 2H<sub>2</sub>O
  
 
Potassium manganate converts into purple [[potassium permanganate]] in [[aqueous]] [[acid]]ic solution:
 
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
+
:3MnO<sub>4</sub><sup>2−</sup> + 4H<sup>+</sup> → 2MnO<sub>4</sub><sup>−</sup> + MnO<sub>2</sub> + 2H<sub>2</sub>O
  
 
==References==
 
==References==
 
{{reflist}}
 
{{reflist}}
−
 
−
==Sources==
 
−
* Oosterhoeks Encyclopedie (Dutch)
 
  
 
==External links==
 
==External links==
 +
*{{ICSC|01|75}}
 +
*{{OrgSynth preps|id=33430|name=manganese dioxide}}
 +
*{{NPI|id=52|name=Manganese and compounds}}
 
* [http://www.mn-consortium.org/ REACH Mn Consortium]
 
* [http://www.mn-consortium.org/ REACH Mn Consortium]
−
* [http://www.orgsyn.org/orgsyn/chemname.asp?nameID=33430 Index of Organic Synthesis procedures utilizing MnO<sub>2</sub>]
 
 
* [http://www.organic-chemistry.org/chemicals/oxidations/manganese(IV)oxide.shtm Example Reactions with Mn(IV) oxide]
 
* [http://www.organic-chemistry.org/chemicals/oxidations/manganese(IV)oxide.shtm Example Reactions with Mn(IV) oxide]
−
* [http://www.npi.gov.au/database/substance-info/profiles/52.html National Pollutant Inventory - Manganese and compounds Fact Sheet]
 
−
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0175.htm International Chemical Safety Card 0175]
 
 
*[http://web.archive.org/web/20041124065033/ceramic-materials.com/cermat/education/139.html Potters Manganese Toxicity by Elke Blodgett]
 
*[http://web.archive.org/web/20041124065033/ceramic-materials.com/cermat/education/139.html Potters Manganese Toxicity by Elke Blodgett]
−
 
−
{{Manganese compounds}}
 
  
 
[[Category:Manganese compounds]]
 
[[Category:Manganese compounds]]

Latest revision as of 13:01, 24 August 2009

Manganese dioxide
Manganese dioxide
IUPAC name Manganese dioxide
Other names Pyrolusite
Manganese(IV) oxide
Identifiers
InChI InChI=1/Mn.2O/rMnO2/c2-1-3
InChIKey NUJOXMJBOLGQSY-MQJJFXMEAL
Standard InChI InChI=1S/Mn.2O
Standard InChIKey NUJOXMJBOLGQSY-UHFFFAOYSA-N
CAS number [1313-13-9]
EC number 215-202-6
RTECS OP0350000
PubChem 14801
Properties[1]
Chemical formula MnO2
Molar mass 86.937 g/mol
Appearance black solid
Density 5.026 g/cm3
Melting point

535 °C decomp.

Solubility in water insoluble
Thermochemistry[2]
Std enthalpy of formation ΔfHo298 −519.5 kJ/mol
Standard molar entropy So298 53.0 J K−1 mol−1
Hazards[3]
Material safety data sheet (MSDS) ICSC 0175
EU index number 025-001-00-3
GHS pictograms Acute Tox. (oral, inhal.) 4
GHS signal word WARNING
GHS hazard statements H302, H332
GHS precautionary statements P264, P270, P261, P271, P301+312, P330, P304+340, P501
Flash point non-flammable
Related compounds
Other anions Manganese disulfide
Other cations Technetium dioxide
Rhenium dioxide
Other manganese oxides Manganese(II) oxide
Manganese(II,III) oxide
Manganese(III) oxide
Manganese heptoxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Manganese dioxide is the inorganic compound with the formula MnO2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese. It is also present in manganese nodules. The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the zinc–carbon battery.[4] In 1976 this application accounted for 500,000 tonnes of pyrolusite. MnO2 is also used for production of MnO4−. It is used extensively as an oxidizing agent in organic synthesis, for example, for the oxidation of allylic alcohols.

Structure

a resinoid crystal of the manganese dioxide generated in the crack of the limestone of mud from Solnhofen, Bayern, Germany.

A number of polymorphs of MnO2 have been identified. The most common is β-MnO2,(pyrolusite) which has the TiO2, rutile structure.[5] Others are α-MnO2, γ-MnO2, ε-MnO2, and λ-MnO2.[5][6] The structures of all of these forms are closely related and are built from linked MnO6 octahedra and "tunnels" capable of holding cations are formed in all except β-MnO2.[5][6] Interest in these polymorphs is due to their use in lithium ion batteries.

History and chemical reactions

The chemical properties of MnO2 have been well examined since relatively pure materials have long been readily found or prepared. MnO2 was used for production of chlorine in the eighteenth century, before being displaced by electrolytic methods. The manganese dioxide was subsequently recovered by the Weldon process.

MnO2 catalyses several reactions associated with the formation of O2, reminiscent of the role of Mn in the oxygen evolving center. In a classical laboratory demonstration, a mixture of potassium chlorate and manganese dioxide is heated and the oxygen gas collected over water. Manganese dioxide also catalyses the decomposition of hydrogen peroxide to oxygen and water:

2H2O2 → O2 + 2H2O

In molten KOH in the presence of oxygen, MnO2 reacts to give the manganate anion.

Manganese dioxide decomposes above about 530 ºC to give manganese(III) oxide and oxygen, while hot concentrated sulfuric or hydrochloric acid reduce the MnIV to manganese(II).[4]

2MnO2 + 2H2SO4 → 2MnSO4 + O2 + 2H2O
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O

This latter reaction forms the basis for Scheele's first isolation of chlorine gas in 1774: Scheele used nascent hydrogen chloride, prepared from the reaction of sodium chloride with concentrated sulfuric acid.[7]

MnO2 + 4NaCl + 2H2SO4 → 2Na2SO4 + MnCl2 + Cl2 + 2H2O
Eo (MnO2(s) + 4 H+ + 2 e− ⇌ Mn2+ + 2H2O) = +1.23 V
Eo (Cl2(g) + 2 e− ⇌ 2 Cl−) = +1.36 V

The reaction would not be expected to proceed, based on the standard electrode potentials, but is favoured by the extremely high acidity and the evolution (and removal) of gaseous chlorine.

Production

The natural occuring manganese dioxide contains impurities and a considerable amount of manganese(III) ions. Only a limited number of deposits contain the γ-modification in high enough purity, which is the prefered material for the battery industry. The ferrite production also needs manganese dioxide with only small amounts of impurities. Therfore the production of synthetic manganese dioxide is important. Two groups of methods are used, yielding chemical manganese dioxide (CMD) and electrolytical manganese dioxide (EMD). The CMD is mostly used for the production of ferrites, while the EMD is used for the production of batteries.[8]

Chemical manganese dioxide

One of the two chemical methods starts from natural manganese dioxide and converts it with dinitrogen tetroxide (N2O4) and water to manganese(II) nitrate solution, which is purified and after evaporation of the water a crystaline solid forms. At temperatures of 400 °C the reverse reaction releases the N2O4 and manganese dioxide is formed.[8]

MnO2 + N2O4 → Mn(NO3)2
Mn(NO3)2 → MnO2 + N2O4

In the other chemical process the natural manganeses dioxide ore is reduced with oil or coal to the managanese oxide. The manganese(II) oxide is dissolved in sulfuric acid and after purification the manganese(II) is precipitated as carbonate by adding ammonium carbonate. The carbonate is heated with air and a manganese oxide forms, which is a mixture between manganese(II) and manganese(IV) oxide. To complete the reaction the oxide is suspended in sulfuric acid and sodium chlorate is added. The chloric acid oxidizes the manganese oxide and chlorine is formed as by-product.[8]

2MnO2 + C → 2MnO + CO2
MnO + H2SO4 → MnSO4 + H2O
MnSO4 + (NH4)2CO3 → MnCO3↓ + (NH4)2SO4
MnCO3 + O2 → MnO1.85 + CO2
MnO1.85 + 2n HClO3 → MnO1.85 + nCl2 + nH2O

Electrolytical manganese dioxide

The electrochemical method starts from the manganese(II) sulfate solution, which is obtained by similar processes mentioned in the previous method, but some producers use hydrogen instead of coal and oil for the reduction. Iron is oxidized by addition of manganese dioxide and precipitates at a pH of 5 to 6, while other ions like cobalt, nickel and copper are precipitated as sulfides. Electrolysis is than used to oxidize the manganese. During that process the manganese dioxide forms a layer on the anode, which is made from titanium, lead or graphite.[8] 

:MnO2 +  H2  →  MnO + H2O
MnO + H2SO4 → MnSO4 + H2O
Mn2+ + H2O → MnO2 + 2e− + 2H+

Applications

Ancient cave painters and later the ancient Egyptians used MnO2 as a black or brown pigment. One of its first uses was in glass making. Egyptian and Roman glasswares have been shown by analyses to contain over 2% manganous oxide. Pliny mentions the use of manganese oxide under the name of "magnes" among the Romans for decolorizing glass. He considered it a variety of lodestone or magnetic iron ore.[9] Eighteenth-century British chemists referred to MnO2 simply as manganese.[ref. needed]

In modern times, the predominant application of MnO2 is as a component of dry cell batteries, so called zinc–carbon batteries. Approximately 500,000 tonnes are consumed for this application annually. Two distinct synthetic forms of the dioxide are used for batteries, chemical manganese dioxide (CMD) and electrolytic manganese dioxide (EMD).[10]

MnO2 in organic synthesis

A specialized use of manganese dioxide is as an oxidant in organic synthesis.[11] 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 factor.[12] The mineral pyrolusite makes a poor reagent. Usually, however, the reagent is generated by treatment of an aqueous solution KMnO4 with a Mn(II) salt, typically the sulfate. MnO2 oxidizes allylic alcohols to the corresponding aldehydes:

cis-RCH=CHCH2OH + MnO2 → cis-RCH=CHCHO + “MnO” + H2O

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 MnO2 to dialdehydes or diketones. Otherwise, the applications of MnO2 are numerous, being applicable to many kinds of reactions including amine oxidation, aromatization, oxidative coupling, and thiol oxidation.

Precursor to permanganate

The green salt potassium manganate is obtained in minutes when a solution of MnO2 in molten KOH or NaOH is treated with oxidizing agents such as potassium nitrate (KNO3), potassium perchlorate (KClO4), or even oxygen gas.[10]

2MnO2 + 4OH− + O2 → 2MnO42− + 2H2O

Potassium manganate converts into purple potassium permanganate in aqueous acidic solution:

3MnO42− + 4H+ → 2MnO4− + MnO2 + 2H2O

References

  1. ↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p B-118. ISBN 0-8493-0462-8.
  2. ↑ Jolly, William L. Modern Inorganic Chemistry, 2nd ed.; McGraw-Hill: New York, 1991; p 586. ISBN 0-07-032768-8.
  3. ↑ Index no. 025-001-00-3 of Annex VI, Part 3, to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. OJEU L353, 31.12.2008, pp 1–1355 at p 420.
  4. ↑ 4.0 4.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1218–20. ISBN 0-08-022057-6.
  5. ↑ 5.0 5.1 5.2 Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon Press: Oxford, 1984. ISBN 0-19-855370-6.
  6. ↑ 6.0 6.1 Fong, G. C.; Kennedy, B. J.; Elcombe, M. M. A powder neutron diffraction study of λ- and γ-manganese dioxide and of LiMn2O4. Z. Kristallogr. 1994, 209 (12), 941–45.
  7. ↑ Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 923. ISBN 0-08-022057-6.
  8. ↑ 8.0 8.1 8.2 8.3 Preisler, Eberhard Moderne Verfahren der Großchemie: Braunstein. Chemie in unserer Zeit 1980, 14, 137–48. DOI: 10.1002/ciuz.19800140502.
  9. ↑ Harder, Edmund Cecil Manganese Deposits of the United States with Sections on Foreign Deposits, Chemistry, and Uses; Bulletin of the United States Geological Survey 427; Government Printing Office: Washington, DC, 1910, <http://www.archive.org/details/manganesedeposi00hardgoog>.
  10. ↑ 10.0 10.1 Reidies, Arno H. Manganese Compounds. In Ullmann's Encyclopedia of Industrial Chemistry; Wiley-VCH: Weinheim, 2002; Vol. 20, pp 495–542. ISBN 3-527-30385-5. DOI: 10.1002/14356007.a16_123.
  11. ↑ Cahiez, G.; Alami, M.; Taylor, R. J. K.; Reid, M.; Foot, J. S. Manganese Dioxide. In Encyclopedia of Reagents for Organic Synthesis; Paquette, Leo A., Ed.; John Wiley: New York, 2004.
  12. ↑ Attenburrow, J.; Cameron, A. F. B.; Chapman, J. H.; Evans, R. M.; Hems, B. A.; Jansen, A. B. A.; Walker, T. A synthesis of vitamin a from cyclohexanone. J. Chem. Soc. 1952, 1094–11. DOI: 10.1039/JR9520001094.

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