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WIKIBOOKS
DISPONIBILI
?????????

ART
- Great Painters
BUSINESS&LAW
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- Fundamentals of Law
- Marketing
- Shorthand
CARS
- Concept Cars
GAMES&SPORT
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MEDICINE
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MUSIC&DANCE
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SCIENCE
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LIFESTYLE
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TRADITIONS
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NATURE
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ARTICLES IN THE BOOK

  1. AAAA battery
  2. AAA battery
  3. AA battery
  4. A battery
  5. Absorbent glass mat
  6. Alessandro Volta
  7. Alkaline battery
  8. Alkaline fuel cell
  9. Aluminium battery
  10. Ampere
  11. Atomic battery
  12. Backup battery
  13. Baghdad Battery
  14. Batteries
  15. Battery charger
  16. B battery
  17. Bernard S. Baker
  18. Beta-alumina solid electrolyte
  19. Betavoltaics
  20. Bio-nano generator
  21. Blue energy
  22. Bunsen cell
  23. Car battery
  24. C battery
  25. Clark cell
  26. Concentration cell
  27. Coulomb
  28. 2CR5
  29. Daniell cell
  30. Direct borohydride fuel cell
  31. Direct-ethanol fuel cell
  32. Direct methanol fuel cell
  33. Dry cell
  34. Dry pile
  35. Duracell
  36. Duracell Bunny
  37. Earth battery
  38. Electric charge
  39. Electric current
  40. Electricity
  41. Electrochemical cell
  42. Electrochemical potential
  43. Electro-galvanic fuel cell
  44. Electrolysis
  45. Electrolyte
  46. Electrolytic cell
  47. Electromagnetism
  48. Electromotive force
  49. Energizer Bunny
  50. Energy
  51. Energy density
  52. Energy storage
  53. Flashlight
  54. Float charging
  55. Flow Battery
  56. Formic acid fuel cell
  57. Fuel cell
  58. Fuel cell bus trial
  59. Galvanic cell
  60. Gel battery
  61. Grove cell
  62. Half cell
  63. History of the battery
  64. Hybrid vehicle
  65. Lead-acid battery
  66. Leclanché cell
  67. Lemon battery
  68. List of battery sizes
  69. List of battery types
  70. List of fuel cell vehicles
  71. Lithium battery
  72. Lithium ion batteries
  73. Lithium iron phosphate battery
  74. Lithium polymer cell
  75. LR44 battery
  76. Luigi Galvani
  77. Manganese dioxide
  78. Memory effect
  79. Mercury battery
  80. Metal hydride fuel cell
  81. Methane reformer
  82. Methanol reformer
  83. Michael Faraday
  84. Microbial fuel cell
  85. Molten carbonate fuel cell
  86. Molten salt battery
  87. Nickel-cadmium battery
  88. Nickel-iron battery
  89. Nickel metal hydride
  90. Nickel-zinc battery
  91. Open-circuit voltage
  92. Optoelectric nuclear battery
  93. Organic radical battery
  94. Oxyride battery
  95. Panasonic EV Energy Co
  96. Peukert's law
  97. Phosphoric acid fuel cell
  98. Photoelectrochemical cell
  99. Polymer-based battery
  100. Power density
  101. Power management
  102. Power outage
  103. PP3 battery
  104. Primary cell
  105. Prius
  106. Proton exchange membrane
  107. Proton exchange membrane fuel cell
  108. Protonic ceramic fuel cell
  109. Radioisotope piezoelectric generator
  110. Ragone chart
  111. RCR-V3
  112. Rechargeable alkaline battery
  113. Reverse charging
  114. Reversible fuel cell
  115. Searchlight
  116. Secondary cell
  117. Short circuit
  118. Silver-oxide battery
  119. Smart Battery Data
  120. Smart battery system
  121. Sodium-sulfur battery
  122. Solid oxide fuel cell
  123. Super iron battery
  124. Thermionic converter
  125. Trickle charging
  126. Vanadium redox battery
  127. Volt
  128. Voltage
  129. Voltaic pile
  130. Watch battery
  131. Water-activated battery
  132. Weston cell
  133. Wet cell
  134. Zinc-air battery
  135. Zinc-bromine flow battery
  136. Zinc-carbon battery

 

 
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BATTERIES
This article is from:
http://en.wikipedia.org/wiki/Manganese_dioxide

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Manganese(IV) oxide

From Wikipedia, the free encyclopedia

(Redirected from Manganese dioxide)

Manganese(IV) oxide is the chemical compound MnO2, more usually 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.

Other oxides of manganese (see Manganate)

The green salt potassium manganate is obtained after about 10 minutes when a solution of MnO2 in molten KOH or NaOH is treated with oxidizing agents such as saltpeter (potassium nitrate KNO3) or potassium perchlorate (KClO4).

2MnO2 + 4OH + O2 → 2MnO42– + 2H2O

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

MnO2 in organic synthesis

Manganese dioxide is widely used as an oxidant in organic synthesis. Forms of MnO2 useful as an oxidizing reagent is not a straightforwardly stoichiometric reagent, far from it. The method of reagent preparation, sample history, and solvents are serious considerations. These problems are typical for many heterogeneous reagents where surface area, among other variables, is a significant variable. Compounding this problem, MnO2 exists in various crystalline forms and is not stoichiometric, being better described as MnO2-x(H2O)n where 0<x<0.5 and n can be nonzero. The mineral pyrolusite makes a poor reagent. A variety of recipes exist for "MnO2." 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 brown precipitate of “manganese dioxide” is dried and activated thermally. It is used in anywhere from 5-50x excess relative to the substrate. Typical solvents are aromatic hydrocarbons, chlorocarbons, diethyl ether, THF, acetone, hexane, and ethyl acetate.

The predominant application of MnO2 is for the oxidation of allylic alcohols to the corresponding aldehydes. Assuming that MnO2 is stoichiometric (and it is not in reality, which is why it is used in excess quantities in synthetic organic chemical reactions) the reaction equation would take the following balanced form:

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:

  • MnO2is used as a catalyst in the laboratory preparation of oxygen from potassium chlorate, a classical experiment of elementary chemistry classes. The procedure consists of merely heating potassium chlorate and manganese dioxide together in a hard glass container and collecting the gas over water. See oxygen, manganese and potassium chlorate for precautions. 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 sometimes used MnO2 as black paint.
  • The MnO2 was used for production of chlorine in the eighteenth century, before being displaced by eletrolytic methods. The Mn recovery process used in connection with such production is called the Weldon process.
  • The earliest glassmakers used manganese to remove the natural blueish-green tint of glass or to add a pinkish or purplish color.

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

  • Index of Organic Synthesis procedures utilizing MnO2
  • National Pollutant Inventory - Manganese and compounds Fact Sheet
  • PubChem summary of MnO2
  • International Chemical Safety Card 0175
  • Links to external chemical sources
Retrieved from "http://en.wikipedia.org/wiki/Manganese%28IV%29_oxide"