Manganese (IV) oxide

Crystal structure
__ Mn 4+      __ O 2−
General
Surname	Manganese (IV) oxide
other names	Manganese dioxide Brownstone Akhtenskit Pyrolusite Ramsdellite Magnesia nigra Manganese peroxide
Ratio formula	MnO 2
Brief description	black-brown solid
External identifiers / databases
CAS number 1313-13-9 EC number 215-202-6 ECHA InfoCard 100,013,821 PubChem 14801 Wikidata Q407674
properties
Molar mass	86.94 g mol −1
Physical state	firmly
density	5.03 g cm −3
Melting point	535 ° C (decomposition)
solubility	almost insoluble in water
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 302 + 332-373 P: 314
MAK	0.5 mg m −3
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Manganese (IV) oxide , also called manganese dioxide or brownstone, is an oxide of manganese with the empirical formula MnO ₂ . Manganese is in the +4 oxidation state. Because of its appearance (dark brown, shiny, silky, grainy to earthy) it is also known as Magnesia nigra, black magnesia, or, somewhat imprecisely, brownstone. However, brownstone is a group of manganese minerals whose main component is manganese dioxide.

history

Manganese (IV) oxide was formerly artisans as " glass , referred wheeler soap" as it through (III) silicates iron could discolor discolored glass melts. Already in the glasses of the ancient Egyptians and Romans you can find around 2% manganese oxide. Brownstone was probably already used to discolour glasses at this time.

Occurrence

Manganese (IV) oxide is found as orthorhombically crystallized ramsdellite , as tetragonally crystallized pyrolusite ( soft manganese ore ) and as hexagonally crystallized Akhtenskite on a large scale in the southern Urals and in South Africa. Together with other iron compounds, it is often a major component of umbra and other brown, dark-colored soils.

Extraction and presentation

Manganese (IV) oxide is produced by grinding pyrolusite or by heating manganese (II) nitrate in air to over 500 ° C.

${\displaystyle \mathrm {Mn(NO_{3})_{2}\cdot 6\ H_{2}O\ {\xrightarrow {\Delta T}}\ MnO_{2}+2\ NO_{2}+6\ H_{2}O} }$

Today, however, manganese (IV) oxide is mainly obtained by electrolysis of a solution of manganese (II) sulfate . Bivalent manganese ions (Mn ²⁺ ) oxidize on the anode to trivalent Mn ³⁺ ions, which then disproportionate to Mn ²⁺ and Mn ⁴⁺ ions . Brown stone is deposited on the anode.

properties

Manganese (IV) oxide

Manganese (IV) oxide is a brown-black powder that is insoluble in water . In addition, there is no reaction with cold sulfuric or nitric acid . Manganese (IV) oxide usually crystallizes in the rutile structure , although it is found in other structures as well, as described in the article on manganese dioxide.

Reactions

By heating above 450 ° C, manganese (III) oxide (Mn ₂ O ₃ ) is formed with release of oxygen .

${\displaystyle \mathrm {4\ MnO_{2}\ {\xrightarrow {\Delta T}}\ 2\ Mn_{2}O_{3}+O_{2}} }$

By heating above 600 ° C, manganese (II, III) oxide (Mn ₃ O ₄ ) is formed with release of oxygen ; Mn ₃ O ₄ contains 72% manganese.

${\displaystyle \mathrm {3\ MnO_{2}\ {\xrightarrow {\Delta T}}\ Mn_{3}O_{4}+O_{2}} }$

Heating with the addition of sulfuric acid leads to the elimination of oxygen with the formation of manganese (II) sulfate.

${\displaystyle \mathrm {2\ MnO_{2}+2\ H_{2}SO_{4}\ {\xrightarrow {\Delta T}}\ 2\ MnSO_{4}+O_{2}+2\ H_{2}O} }$

Hydrogen peroxide decomposes in the presence of manganese dioxide, releasing oxygen. The manganese dioxide acts as a catalyst .

${\displaystyle \mathrm {2\ H_{2}O_{2}\ \xrightarrow {MnO_{2}} } }$ ${\displaystyle \mathrm {2\ H_{2}O+O_{2}} }$

Manganese dioxide reacts with hydrochloric acid to form manganese (II) chloride , producing chlorine . This implementation was important as a Weldon process for the production of chlorine.

${\displaystyle \mathrm {MnO_{2}+4\ HCl\longrightarrow MnCl_{2}+Cl_{2}+2\ H_{2}O} }$

use

Manganese dioxide dendrites on a layer of limestone from Solnhofen , Bavaria.

Because of its oxidizing effect, manganese dioxide is often used as an oxidizing agent . For example, it is used in the organic synthesis of hydroquinone from aniline . Manganese dioxide is the active component of the hardener paste for sealants based on polysulphides and causes the oxidative linkage via the SH groups of the polysulphide prepolymer. It is used in European safety matches as a burn rate catalyst and replaces more toxic substances such as potassium dichromate . It is also used as an oxidizing agent in fireworks. It is also used in the laboratory to represent halogens from corresponding hydrogen halides.

${\displaystyle \mathrm {MnO_{2}+4\ HX\longrightarrow MnX_{2}+X_{2}+2\ H_{2}O} }$

It is also known as "glassmaker's soap" in glass production . Small amounts of manganese dioxide are added to glass melts, which are often colored yellow-green by small amounts of iron (III) silicates , to neutralize the discoloration. Manganese (III) silicates are formed, the color of which is violet. However, yellow-green and purple are complementary colors, which is why the melt flow appears in a neutral hue (grayish to almost colorless).

It is used as a cathode material in batteries . In zinc-carbon and alkaline-manganese batteries , either

• n Of course occurring M angan d ioxid ( "NMD"),
• c hemisch manufactured M angan d ioxid ( "CMD") or
• by E lektrolyse manufactured M angan d used ioxid ( "EMD").

Other uses are as a coloring agent for bricks , part of gas cleaning in respiratory masks and as an additive in the production of varnishes and siccatives . It also has a catalytic effect in the decomposition of hydrogen peroxide and thus serves to produce steam and oxygen .

Manganese dioxide hydrate

Precipitation of manganese (IV) oxide hydroxide with sodium peroxide from manganese (II) sulfate solution

Manganese dioxide hydrate (manganese (IV) oxide hydroxide) is obtained by oxidative precipitation from manganese (II) salt solutions with sodium hydroxide and hydrogen peroxide or with sodium peroxide as a dark brown precipitate:

${\displaystyle \mathrm {Mn^{2+}+2\ OH^{-}+H_{2}O_{2}\longrightarrow MnO(OH)_{2}+H_{2}O} }$

This compound is important because, unlike anhydrous manganese dioxide, it is more reactive as an oxidizing agent .

Individual evidence

1. ↑ Entry on manganese dioxide. In: Römpp Online . Georg Thieme Verlag, accessed on November 12, 2014.
2. ↑ ^{a b c d e f} Entry on manganese (IV) oxide in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
3. ↑ Entry on Manganese dioxide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ ^{a b} arche-kurzmann.de: The fairy tale of the discoloration of glass , accessed on February 5, 2013.
5. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 436.
6. ^ ^{A b c d} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .
7. ↑ Alexander P. Hardt: Pyrotechnics , Pyrotechnica Publications, Post Falls Idaho USA 2001, ISBN 0-929388-06-2 , pp. 74 ff.
8. ^ Heinrich Remy : Textbook of Inorganic Chemistry Volume II , Akademische Verlagsgesellschaft Geest & Portig Leipzig 1961, p. 258
9. ↑ Jander-Blasius: Textbook of analytical and preparative inorganic chemistry , 5th edition, S. Hirzel, Stuttgart-Leipzig 1965, p. 209.
10. ↑ Eberhard Schweda: Jander / Blasius, Inorganische Chemie I, 17th edition, 2012, p. 202