Manganese dioxide
Names | |
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IUPAC names
Manganese dioxide
Manganese(IV) oxide | |
Other names
Pyrolusite, hyperoxide of manganese, black oxide of manganese, manganic oxide
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Identifiers | |
3D model (
JSmol ) |
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ChEBI | |
ChemSpider | |
ECHA InfoCard
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100.013.821 |
EC Number |
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PubChem CID
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RTECS number
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
MnO 2 | |
Molar mass | 86.9368 g/mol |
Appearance | Brown-black solid |
Density | 5.026 g/cm3 |
Melting point | 535 °C (995 °F; 808 K) (decomposes) |
Insoluble | |
+2280.0×10−6 cm3/mol[1] | |
Structure[2] | |
Tetragonal, tP6, No. 136 | |
P42/mnm | |
a = 0.44008 nm, b = 0.44008 nm, c = 0.28745 nm
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Formula units (Z)
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2 |
Thermochemistry[3] | |
Heat capacity (C)
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54.1 J·mol−1·K−1 |
Std molar
entropy (S⦵298) |
53.1 J·mol−1·K−1 |
Std enthalpy of (ΔfH⦵298)formation |
−520.0 kJ·mol−1 |
Gibbs free energy (ΔfG⦵)
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−465.1 kJ·mol−1 |
Hazards | |
GHS labelling: | |
Warning | |
H302, H332 | |
P261, P264, P270, P271, P301+P312, P304+P312, P304+P340, P312, P330, P501 | |
NFPA 704 (fire diamond) | |
Flash point | 535 °C (995 °F; 808 K) |
Safety data sheet (SDS) | ICSC 0175 |
Related compounds | |
Other anions
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Manganese disulfide |
Other cations
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Rhenium dioxide
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Manganese(II) oxide Manganese(II,III) oxide Manganese(III) oxide Manganese heptoxide | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Manganese dioxide is the
2 as a possible cathode for lithium-ion batteries.[5][6]
Structure
Several
2 in organic synthesis.[7] The α-polymorph of MnO
2 has a very open structure with "channels", which can accommodate metal ions such as silver or barium. α-MnO
2 is often called hollandite
Production
Naturally occurring manganese dioxide contains impurities and a considerable amount of
Chemical manganese dioxide
One method starts with natural manganese dioxide and converts it using dinitrogen tetroxide and water to a manganese(II) nitrate solution. Evaporation of the water leaves the crystalline nitrate salt. At temperatures of 400 °C, the salt decomposes, releasing N
2O
4 and leaving a residue of purified manganese dioxide.[8] These two steps can be summarized as:
- MnO
2 + N
2O
4 ⇌ Mn(NO
3)
2
In another process, manganese dioxide is
Lastly, the action of
- 2 KMnO
4 + 3 MnSO
4 + 2 H
2O→ 5 MnO
2 + K
2SO
4 + 2 H
2SO
4
Electrolytic manganese dioxide
Electrolytic manganese dioxide (EMD) is used in
Reactions
The important reactions of MnO
2 are associated with its redox, both oxidation and reduction.
Reduction
MnO
2 is the principal
- MnO
2 + 2 C → Mn + 2 CO
The key redox reactions of MnO
2 in batteries is the one-electron reduction:
- MnO
2 + e− + H+
→ MnO(OH)
MnO
2
- 2 H
2O
2 → 2 H
2O + O
2
Manganese dioxide decomposes above about 530 °C to
3O
4 forms. Higher temperatures give MnO, which is reduced only with difficulty.[11]
Hot concentrated sulfuric acid reduces MnO
2 to manganese(II) sulfate:[4]
- 2 MnO
2 + 2 H
2SO
4 → 2 MnSO
4 + O
2 + 2 H
2O
The reaction of hydrogen chloride with MnO
2 was used by Carl Wilhelm Scheele in the original isolation of chlorine gas in 1774:
- MnO
2 + 4 HCl → MnCl
2 + Cl
2 + 2 H
2O
As a source of hydrogen chloride, Scheele treated sodium chloride with concentrated sulfuric acid.[4]
- E
o(MnO
2(s) + 4 H+
+ 2 e− ⇌ Mn2+ + 2 H
2O) = +1.23 V - E
o(Cl
2(g) + 2 e− ⇌ 2 Cl−) = +1.36 V
- E
The
]), but it is favoured by the lower pH
This reaction is also a convenient way to remove the manganese dioxide
Oxidation
Heating a mixture of KOH and MnO
2 in air gives green potassium manganate:
- 2 MnO
2 + 4 KOH + O
2 → 2 K
2MnO
4 + 2 H
2O
Potassium manganate is the precursor to potassium permanganate, a common oxidant.
Occurrence and applications
The predominant application of MnO
2 is as a component of
Prehistory
Excavations at the Pech-de-l'Azé cave site in southwestern France have yielded blocks of manganese dioxide writing tools, which date back 50,000 years and have been attributed to Neanderthals . Scientists have conjectured that Neanderthals used this mineral for body decoration, but there are many other readily available minerals that are more suitable for that purpose. Heyes et al. (in 2016) determined that the manganese dioxide lowers the combustion temperatures for wood from above 650 °F to 480 °F, making fire making much easier and this is likely to be the purpose of the blocks.[14]
Organic synthesis
A specialized use of manganese dioxide is as oxidant in
- cis-RCH=CHCH
2OH + MnO
2 → cis-RCH=CHCHO +MnO+ H
2O
- cis-RCH=CHCH
The configuration of the
2 are numerous, being applicable to many kinds of reactions including amine oxidation, aromatization, oxidative coupling, and thiol
Microbiology
In Geobacteraceae sp., MnO2 functions as an electron acceptor coupled to the oxidation of organic compounds. This theme has implications for bioremediation.[17]
See also
References
- ^ Rumble, p. 4.71
- .
- ^ Rumble, p. 5.25
- ^ ISBN 978-0-08-022057-4..
- hdl:10533/173039.
- .
- ^ ISBN 9780470842898.
- ^ .
- ^ Arthur Sutcliffe (1930) Practical Chemistry for Advanced Students (1949 Ed.), John Murray – London.
- .
- ^ ISBN 3527306730.
- ISBN 978-3-527-30385-4
- ISSN 1385-8947.
- ^ "Neandertals may have used chemistry to start fires". www.science.org. Retrieved 2022-05-30.
- .
- ^ Paquette, Leo A. and Heidelbaugh, Todd M. "(4S)-(−)-tert-Butyldimethylsiloxy-2-cyclopen-1-one". Organic Syntheses
{{cite journal}}
: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 9, p. 136. (this procedure illustrates the use of MnO2 for the oxidation of an allylic alcohol) - PMID 15518832.
Cited sources
- Rumble, John R., ed. (2018). ISBN 978-1-1385-6163-2.