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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 per cent of 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.[4] Eighteenth-century British chemists referred to MnO2 simply as manganese.[citation needed]
In modern times, the predominant application of MnO2 is as a component of dry cell batteries. Approximately 500M kg 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).[5]
A specialized use of manganese dioxide is as an oxidant in organic synthesis.[6] 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.[7] 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 MnO
2 to dialdehydes or diketones. Otherwise, the applications of MnO
2 are numerous, being applicable to many kinds of reactions including amine oxidation, aromatization, oxidative coupling, and thiol oxidation
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http://en.wikipedia.org/wiki/Manganese_dioxide