Manganese dioxide is the
inorganic compound with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
. This blackish or brown solid occurs naturally as the mineral
pyrolusite, which is the main ore of
manganese
Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
and a component of
manganese nodules. The principal use for is for dry-cell
batteries
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
, such as the
alkaline battery and the
zinc–carbon battery.
[.] is also used as a
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
and as a precursor to other manganese compounds, such as . It is used as a
reagent in
organic synthesis, for example, for the oxidation of
allylic
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...
alcohols. is α polymorph that can incorporate a variety of atoms (as well as water molecules) in the "tunnels" or "channels" between the manganese oxide octahedra. There is considerable interest in as a possible cathode for
lithium-ion batteries.
Structure
Several
polymorphs of are claimed, as well as a hydrated form. Like many other dioxides, crystallizes in the
rutile crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pattern ...
(this polymorph is called
pyrolusite or ), with three-coordinate oxide and octahedral metal centres.
[ is characteristically nonstoichiometric, being deficient in oxygen. The complicated solid-state chemistry of this material is relevant to the lore of "freshly prepared" in organic synthesis.][ The α-polymorph of has a very open structure with "channels" which can accommodate metal atoms such as silver or barium. is often called hollandite, after a closely related mineral.
]
Production
Naturally occurring manganese dioxide contains impurities and a considerable amount of manganese(III) oxide. Production of batteries
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
and ferrite (two of the primary uses of manganese dioxide) requires high purity manganese dioxide. Batteries require "electrolytic manganese dioxide" while ferrites require "chemical manganese dioxide".[.]
Chemical manganese dioxide
One method starts with natural manganese dioxide and converts it using dinitrogen tetroxide
Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russia rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...
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 and leaving a residue of purified manganese dioxide. These two steps can be summarized as:
: +
In another process manganese dioxide is carbothermically reduced to manganese(II) oxide which is dissolved in sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
. The filtered solution is treated with ammonium carbonate to precipitate . The carbonate is calcined in air to give a mixture of manganese(II) and manganese(IV) oxides. To complete the process, a suspension of this material in sulfuric acid is treated with sodium chlorate. Chloric acid, which forms in situ, converts any Mn(III) and Mn(II) oxides to the dioxide, releasing chlorine as a by-product.
Lastly, the action of potassium permanganate over manganese sulfate
Manganese(II) sulfate usually refers to the inorganic compound with the formula MnSO4·H2O. This pale pink deliquescent solid is a commercially significant manganese(II) salt. Approximately 260,000 tonnes of manganese(II) sulfate were produced wor ...
crystals produces the desired oxide.
:2 + 3 + 2 → 5 + + 2
Electrolytic manganese dioxide
Electrolytic manganese dioxide (EMD) is used in zinc–carbon batteries together with zinc chloride
Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. This salt is hygroscopic ...
and ammonium chloride. EMD is commonly used in zinc manganese dioxide rechargeable alkaline (Zn RAM) cells also. For these applications, purity is extremely important. EMD is produced in a similar fashion as electrolytic tough pitch (ETP) copper: The manganese dioxide is dissolved in sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
(sometimes mixed with manganese sulfate
Manganese(II) sulfate usually refers to the inorganic compound with the formula MnSO4·H2O. This pale pink deliquescent solid is a commercially significant manganese(II) salt. Approximately 260,000 tonnes of manganese(II) sulfate were produced wor ...
) and subjected to a current between two electrodes. The MnO2 dissolves, enters solution as the sulfate, and is deposited on the anode.
Reactions
The important reactions of are associated with its redox, both oxidation and reduction.
Reduction
is the principal precursor
Precursor or Precursors may refer to:
* Precursor (religion), a forerunner, predecessor
** The Precursor, John the Baptist
Science and technology
* Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of u ...
to ferromanganese and related alloys, which are widely used in the steel industry. The conversions involve carbothermal reduction using coke:
: + 2 C → Mn + 2 CO
The key redox reactions of in batteries is the one-electron reduction:
: + e− + → MnO(OH)
catalyses several reactions that form . In a classical laboratory demonstration, heating a mixture of potassium chlorate and manganese dioxide produces oxygen gas. Manganese dioxide also catalyses the decomposition of hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...
to oxygen and water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
:
:2 → 2 +
Manganese dioxide decomposes above about 530 °C to manganese(III) oxide and oxygen. At temperatures close to 1000 °C, the mixed-valence compound
Mixed valence complexes contain an element which is present in more than one oxidation state. Well-known mixed valence compounds include the Creutz–Taube complex, Prussian blue, and molybdenum blue. Many solids are mixed-valency including in ...
forms. Higher temperatures give MnO, which is reduced only with difficulty.[
Hot concentrated ]sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
reduces to manganese(II) sulfate:
:2 + 2 → 2 + + 2
The reaction of hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chlorid ...
with was used by Carl Wilhelm Scheele
Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist.
Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hydr ...
in the original isolation of chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
gas in 1774:
: + 4 HCl → + + 2
As a source of hydrogen chloride, Scheele treated sodium chloride with concentrated sulfuric acid.
::''E''o ((s) + 4 + 2 e− Mn2+ + 2 ) = +1.23 V
::''E''o ((g) + 2 e− 2 Cl−) = +1.36 V
The standard electrode potentials for the half reactions indicate that the reaction is endothermic
In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...
at pH = 0 (1 M []), but it is favoured by the lower pH as well as the evolution (and removal) of gaseous chlorine.
This reaction is also a convenient way to remove the manganese dioxide precipitate from the ground glass joint
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints ...
s after running a reaction (for example, an oxidation with potassium permanganate).
Oxidation
Heating a mixture of KOH and in air gives green potassium manganate:
:2 + 4 KOH + → 2 + 2
Potassium manganate is the precursor to potassium permanganate, a common oxidant.
Occurrence and applications
The predominant application of is as a component of dry cell
upLine art drawing of a dry cell: 1. brass cap, 2. plastic seal, 3. expansion space, 4. porous cardboard, 5. zinc can, 6. carbon rod, 7. chemical mixture
A dry cell is a type of electric battery, commonly used for portable electrical devices. Unl ...
batteries: alkaline batteries and so called Leclanché cell, or zinc–carbon batteries. Approximately 500,000 tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s are consumed for this application annually. Other industrial applications include the use of as an inorganic pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
in ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...
s and in glassmaking
Glass production involves two main methods – the float glass process that produces sheet glass, and glassblowing that produces bottles and other containers. It has been done in a variety of ways during the history of glass.
Glass contain ...
. It is also used in water treatment applications.
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
Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While ...
. 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.
Organic synthesis
A specialized use of manganese dioxide is as 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 factor. The mineral pyrolusite makes a poor reagent. Usually, however, the reagent is generated in situ by treatment of an aqueous solution with a Mn(II) salt, typically the sulfate. oxidizes allylic
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...
alcohols to the corresponding aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
s or ketones:
::cis-RCH= + → cis-RCH=CHCHO + MnO +
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
In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group.
Nomenclature
In IUPAC nomenclature, the prefix benzyl refers to a substi ...
and even unactivated alcohols are also good substrates. 1,2- Diols are cleaved by to dialdehydes or diketone
In organic chemistry, a dicarbonyl is a molecule containing two carbonyl () groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbony ...
s. Otherwise, the applications of are numerous, being applicable to many kinds of reactions including amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
oxidation, aromatization, oxidative coupling, and thiol oxidation.
Microbiology
In ''Geobacteraceae'' sp., MnO2 functions as an electron acceptor coupled to the oxidation of organic compounds. This theme has implications for bioremediation.
See also
* List of inorganic pigments
The following list includes commercially or artistically important inorganic pigments of natural and synthetic origin..
Purple pigments
Aluminum pigments
* Ultramarine violet: (PV15) - a synthetic or naturally occurring sulfur containing silic ...
References
Cited sources
*
External links
REACH Mn Consortium
Index of Organic Synthesis procedures utilizing
Example Reactions with Mn(IV) oxide
* ttps://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=14801 PubChem summary of
International Chemical Safety Card 0175
{{DEFAULTSORT:Manganese Dioxide
Manganese(IV) compounds
Oxide minerals
Inorganic pigments
Transition metal oxides
Glass dyes