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Information about Manganese Oxide







Manganese(IV) oxide
IUPAC nameManganese dioxide
Manganese(IV) oxide
Other namesPyrolusite
Identifiers
CAS number1313-13-9
Properties
Molecular formulaMnO2
Molar mass86.9368 g/mol (varies)
Appearanceblack solid
Density5.026 g/cm3, solid
Melting point 535 °C decomp.
Solubility in waterInsoluble
Thermochemistry
Std enthalpy of
formation ΔfHo298		−520.9 kJ/mol
Standard molar
entropy So298		53.1 J.K−1.mol−1
Hazards
EU classificationHarmful (Xn)
NFPA 704
0
0
2
OX
R-phrasesR20/22
S-phrasesS2, S25
Related Compounds
Other anionsManganese disulfide
Other cationsTechnetium dioxide
Rhenium dioxide
Related compoundsManganese(II) oxide
Hausmannite
Manganese(III) oxide
Manganese trioxide
Manganese heptoxide
Except where noted otherwise, data are given for
materials in their standard state
(at 25 C, 100 kPa)


Manganese(IV) oxide is the chemical compound MnO2, 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 nodules. The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery. In 1976 this application accounted for 500,000 tonnes of pyrolusite.[1] MnO2 is also used for production of MnO4–. It is used extensively as an oxidising agent in organic synthesis, for example, for the oxidation of allylic alcohols.

MnO2 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.[1] 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 at various pH’s.

The predominant application of MnO2 is for the oxidation of 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.

Miscellaneous

MnO2 has found many applications and investigations inside and beyond the laboratory. The examples below illustrate some:
  • MnO2 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 H2O2(aq) → O2(g) + 2 H2O(l)
  • Eighteenth-century British chemists referred to MnO2 simply as manganese. Elemental manganese was known as regulus of manganese.
  • Ancient cave painters used MnO2 as a black or brown pigment.
  • The MnO2 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 MnO2 in molten KOH or NaOH is treated with oxidizing agents such as potassium nitrate KNO3), potassium perchlorate (KClO4), or even oxygen gas:
2 MnO2 + 4 OH– + O2 → 2 MnO42– + 2 H2O


Potassium manganate converts into purple potassium permanganate in aqueous acidic solution: 3 MnO42– + 4 H+ → 2 MnO4– + MnO2(s) + 2 H2O

References

  1. Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.). Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4. 
  2. 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



References

1. ^ 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.
IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. It is developed and kept up to date under the auspices of the International Union of Pure and Applied Chemistry (IUPAC).
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Pyrolusite is a mineral consisting essentially of manganese dioxide (MnO2) and is important as an ore of manganese. It is a soft, black, amorphous appearing mineral, often with a granular, fibrous or columnar structure, sometimes forming reniform crusts.
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CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers, CAS RNs or CAS #s.
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A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. A chemical formula is also a short way of showing how a chemical reaction occurs.
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Molar mass, symbol M,[1] is the mass of one mole of a substance (chemical element or chemical compound).[2] It is a physical property which is characteristic of each pure substance.
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In physics, density is mass m per unit volume V—how heavy something is compared to its size. A small, heavy object, such as a rock or a lump of lead, is denser than a lighter object of the same size or a larger object of the same weight, such as pieces of
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The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. Although the phrase would suggest a specific temperature and is commonly and incorrectly used as such in most textbooks and literature, most crystalline compounds
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Solubility is a physical property referring to the ability for a given substance, the solute, to dissolve in a solvent.[1] It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution.
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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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The standard enthalpy of formation or "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at
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In chemistry, the standard molar entropy is the entropy content of one mole of substance, under conditions of standard temperature and pressure (STP).

The standard molar entropy is usually given the symbol So, and the units J mol−1 K
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Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances (as amended) is the main European Union law concerning chemical safety.
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NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. It defines the colloquial "fire diamond" used by emergency personnel to quickly and easily identify the risks posed by nearby hazardous materials.
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R-phrases (short for Risk Phrases) are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations.
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S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. The list was consolidated and republished in Directive 2001/59/EC , where translations into other EU languages may be found.
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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Hausmannite is a complex oxide of manganese containing both di- and tri-valent manganese. The formula can be represented as Mn2+Mn3+2O4. It belongs to the spinel group and forms tetragonal crystals.
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Manganese(VII) oxide is the chemical compound with the formula Mn2O7. This volatile liquid is highly reactive and more often discussed than observed or intentionally prepared. It is a dangerous oxidizer that was first described in 1860.
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standard state of a material is its state at 1 bar (100 kilopascals exactly). This pressure was changed from 1 atm (101.325 kilopascals) by IUPAC in 1990.[1] The standard state of a material can be defined at any given temperature, most commonly 25 degrees Celsius,
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Pyrolusite is a mineral consisting essentially of manganese dioxide (MnO2) and is important as an ore of manganese. It is a soft, black, amorphous appearing mineral, often with a granular, fibrous or columnar structure, sometimes forming reniform crusts.
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2, 3
(oxides: acidic, basic or amphoteric
depending on the oxidation state)
Electronegativity 1.55 (Pauling scale)
Ionization energies
(more) 1st: 717.3 kJmol−1
2nd: 1509.
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Polymetallic nodules, also called manganese nodules, are rock concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core.
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battery is a device consisting of one or more electrochemical cells, which store chemical energy and make it available in an electrical form. There are many types of electrochemical cells, including galvanic cells, electrolytic cells, fuel cells, flow cells, and voltaic cells.
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Alkaline batteries are a type of power cell dependent upon the reaction between zinc and manganese dioxide (Zn/MnO2).

Compared with original
zinc-carbon batteries, while both produce approximately 1.
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A Zinc-carbon dry cell or battery is packaged in a zinc can that serves as both a container and anode. It was developed from the wet Leclanché cell (IPA pronunciation: [lɛklɑːnˈʃei]).
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tonne (t) or metric ton (M/T), also referred to as a metric tonne, is a measurement of mass equal to 1,000 kilograms. It is not an SI unit but is accepted for use with the SI.
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Potassium permanganate is the chemical compound KMnO4. In this salt, manganese is in the +7 oxidation state. The salt is also known as "permanganate of potash." The permanganate ion is a strong oxidizing agent.
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Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed.

This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide, or the
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