Potassium permanganate

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Potassium permanganate
Potassium-permanganate-2004-unit-cell-3D-balls.png
Potassium-permanganate-sample.jpg
Identifiers
CAS number 7722-64-7 YesY
PubChem 516875
ChemSpider 22810 YesY
EC number 231-760-3
UN number 1490
KEGG D02053 N
RTECS number SD6475000
ATC code D08AX06,V03AB18
Jmol-3D images Image 1
Properties
Molecular formula KMnO4
Molar mass 158.034 g/mol
Appearance purplish-bronze-gray needles
magenta–rose in solution
Odor odorless
Density 2.703 g/cm3
Melting point 240 °C (464 °F; 513 K) (decomposes)
Solubility in water 63.8 g/L (20 °C)
250 g/L (65 °C)
Solubility decomposes in alcohol and organic solvents
Refractive index (nD) 1.59
Structure
Crystal structure Orthorhombic
Thermochemistry
Specific
heat capacity
C
119.2 J/mol K
Std molar
entropy
So298
171.7 J K−1 mol−1
Std enthalpy of
formation
ΔfHo298
−813.4 kJ/mol
Gibbs free energy ΔG -713.8 kJ/mol
Hazards
MSDS External MSDS
EU Index 025-002-00-9
EU classification Oxidant (O)
Harmful (Xn)
Dangerous for the environment (N)
Non-Flammable
R-phrases R8, R22, R50/53
S-phrases (S2), S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
Related compounds
Other anions Potassium manganite
Potassium manganate
Other cations Sodium permanganate
Ammonium permanganate
Related compounds Manganese heptoxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO
4
ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely pink or purple solutions, the evaporation of which leaves prismatic purplish-black glistening crystals.[1] In 2000, worldwide production was estimated at 30,000 tonnes.[2] In this compound, manganese is in the +7 oxidation state.

History[edit]

In 1659, Johann Rudolf Glauber fused a mixture of the mineral pyrolusite (Manganese Dioxide: MnO2) and potassium carbonate to obtain a material that, when dissolved in water, gave a green solution (potassium manganate) which slowly shifted to violet and then finally red. This report represents the first description of the production of potassium permanganate.[3] Just under two hundred years later London chemist Henry Bollmann Condy had an interest in disinfectants, and marketed several products including ozonised water. He found that fusing pyrolusite with NaOH and dissolving it in water produced a solution with disinfectant properties. He patented this solution, and marketed it as Condy's Fluid. Although effective, the solution was not very stable. This was overcome by using KOH rather than NaOH. This was more stable, and had the advantage of easy conversion to the equally effective potassium permanganate crystals. This crystalline material was known as Condy's crystals or Condy's powder. Potassium permanganate was comparatively easy to manufacture so Condy was subsequently forced to spend considerable time in litigation in order to stop competitors from marketing products similar to Condy's Fluid or Condy's Crystals.[4]

Early photographers used it as a component of flash powder. It is now replaced with other oxidizers, due to the instability of permanganate mixtures. Aqueous solutions of KMnO4 have been used together with T-Stoff (i.e. 80% hydrogen peroxide) as propellant for the rocket plane Messerschmitt Me 163. In this application, it was known as Z-Stoff. This combination of propellants is sometimes still used in torpedoes.

Structure and preparation[edit]

Potassium permanganate is produced industrially from manganese dioxide, which also occurs as the mineral pyrolusite. The MnO2 is fused with potassium hydroxide and heated in air or with a source of oxygen, like potassium nitrate or chlorate.[2] This process gives potassium manganate, which upon electrolytic oxidation in alkaline media, or by boiling the manganate solution in the presence of carbon dioxide until all the green color is discharged, gives potassium permanganate.[5]

2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O
2 MnO42– + Cl2 → 2 MnO4 + 2 Cl

or:

3 K2MnO4 + 2 CO2 → 2 KMnO4 + 2 K2CO3 + MnO2

In which the potassium permanganate is separated by filtering the insoluble manganese dioxide, evaporating the solution to 1/3 and recrystallizing it.

Permanganate salts can also be generated by treating a solution of Mn2+ ions with strong oxidants such as lead dioxide (PbO2), or sodium bismuthate (NaBiO3). Tests for the presence of manganese exploit the vivid violet color of permanganate produced by these reagents.

KMnO4 forms orthorhombic crystals with constants: a = 910.5 pm, b = 572.0 pm, c = 742.5 pm. The overall motif is similar to that for barium sulfate, with which it forms solid solutions.[6] In the solid (as in solution), each MnO4 centres are tetrahedral. The Mn-O distances are 1.62 Å.[7]

Reactions[edit]

Organic chemistry[edit]

Dilute solutions of KMnO4 convert alkenes into diols (glycols). This behaviour is also used as a qualitative test for the presence of double or triple bonds in a molecule, since the reaction decolorizes the initially purple permanganate solution and generates a brown precipitate (MnO2). It is sometimes referred to as Baeyer's reagent. However, bromine serves better in measuring unsaturation (double or triple bonds) quantitatively, since KMnO4, being a very strong oxidizing agent, can react with a variety of groups.

Under acidic conditions, the alkene double bond is cleaved to give the appropriate carboxylic acid:[8]

CH3(CH2)17CH=CH2 + 2 KMnO4 + 3 H2SO4 → CH3(CH2)17COOH + CO2 + 4 H2O + K2SO4 + 2 MnSO4

Potassium permanganate oxidizes aldehydes to carboxylic acids, such as the conversion of n-heptanal to heptanoic acid:[9]

5 C6H13CHO + 2 KMnO4 + 3 H2SO4 → 5 C6H13COOH + 3 H2O + K2SO4 + 2 MnSO4

Even an alkyl group (with a benzylic hydrogen) on an aromatic ring is oxidized, e.g. toluene to benzoic acid.[10]

5 C6H5CH3 + 6 KMnO4 + 9 H2SO4 → 5 C6H5COOH + 14 H2O + 3 K2SO4 + 6 MnSO4

Glycols and polyols are highly reactive toward KMnO4. For example, addition of potassium permanganate to an aqueous solution of sugar and sodium hydroxide produces the chemical chameleon reaction, which involves dramatic color changes associated with the various oxidation states of manganese. A related vigorous reaction is exploited as a fire starter in survival kits. For example, a mixture of potassium permanganate and glycerol or pulverized glucose ignites readily.[11] Its sterilizing properties are another reason for inclusion of KMnO4 in a survival kit.

By itself, potassium permanganate does not dissolve in many organic solvents. If an organic solution of permanganate is desired, "purple benzene" may be prepared, either by treating a two phase mixture of aqueous potassium permanganate and benzene with a quaternary ammonium salt,[12] or by sequestering the potassium cation with a crown ether.[13]

Reaction with acids[edit]

Concentrated sulfuric acid reacts with KMnO4 to give Mn2O7, which can be explosive.[14] Its reaction with concentrated hydrochloric acid gives chlorine. The Mn-containing products from redox reactions depend on the pH. Acidic solutions of permanganate are reduced to the faintly pink manganese(II) ion (Mn2+) and water. In neutral solution, permanganate is only reduced by three electrons to give MnO2, wherein Mn is in a +4 oxidation state. This is the material that stains one's skin when handling KMnO4. KMnO4 spontaneously reduces in an alkaline solution to green K2MnO4, wherein manganese is in the +6 oxidation state.

A curious reaction occurs upon addition of concentrated sulfuric acid to potassium permanganate. Although no reaction may be apparent, the vapor over the mixture will ignite paper impregnated with alcohol. Potassium permanganate and sulfuric acid react to produce some ozone, which has a high oxidising power and rapidly oxidises the alcohol, causing it to combust. As the reaction also produces explosive Mn2O7, this should only be attempted with great care.[15][16]

Photodecomposition[edit]

Potassium permanganate decomposes when exposed to light:

2 KMnO4 → K2MnO4 + MnO2(s) + O2

Uses[edit]

Almost all applications of potassium permanganate exploit its oxidizing properties.[2] As a strong oxidant that does not generate toxic byproducts, KMnO4 has many niche uses.

Potassium permanganate is one of the principal chemicals used in the film and television industries to "age" props and set dressings. Its oxidising effects create "hundred year old" or "ancient" looks on hessian cloth, ropes, timber and glass.[17]

Water treatment and disinfection[edit]

As an oxidant, potassium permanganate can act as an antiseptic. For example, dilute solutions are used to treat canker sores (ulcers), disinfectant for the hands and treatment for mild pompholyx, dermatitis,[18][19] and fungal infections of the hands or feet.[20] Potassium permanganate is used extensively in the water treatment industry. It is used as a regeneration chemical to remove iron and hydrogen sulfide (rotten egg smell) from well water via a "Manganese Greensand" Filter. "Pot-Perm" is also obtainable at pool supply stores, is used additionally to treat waste water. Historically it was used to disinfect drinking water.[21][22] It currently finds application in the control of nuisance organisms such as Zebra mussels in fresh water collection and treatment systems.[23]

Organic synthesis[edit]

Aside from its use in water treatment, the other major application of KMnO4 is as a reagent for the synthesis of organic compounds.[24] Significant amounts are required for the synthesis of ascorbic acid, chloramphenicol, saccharin, isonicotinic acid, and pyrazinoic acid.[2]

A solution of KMnO4 in water, in a volumetric flask

Analytical use[edit]

Potassium permanganate can be used to quantitatively determine the total oxidisable organic material in an aqueous sample. The value determined is known as the permanganate value. In analytical chemistry, a standardized aqueous solution of KMnO4 is sometimes used as an oxidizing titrant for redox titrations (permanganometry). In a related way, it is used as a reagent to determine the Kappa number of wood pulp. For the standardization of KMnO4 solutions, reduction by oxalic acid is often used.[25]

Aqueous, acidic solutions of KMnO4 are used to collect gaseous mercury in flue gas during stationary source emissions testing.[26]

In histology, potassium permanganate is used to bleach melanin which obscures tissue detail.[citation needed] Pre-treated with potassium permanganate, to obliterate Congo red reactivity, was thought to be definitive for AA amyloidosis;[27] this is now generally considered to be unreliable.[28][29]

Fruit preservation[edit]

Ethylene absorbents extend storage time of bananas even at high temperatures. This effect can be exploited by packing bananas in polyethylene with potassium permanganate as an ethylene absorbent, that doubles a bananas lifespan up to 3–4 weeks without the need for refrigeration.[30][31][32] Ethylene released by the bananas encourage it to ripen; by removing it via oxidation, the bananas' ripening is delayed.

Survival kits[edit]

Potassium permanganate is typically included in survival kits: as a fire starter (mixed with antifreeze from a car radiator or glycerin),[11] water sterilizer, and for creating distress signals on snow.[33]

Safety and handling[edit]

As an oxidizer that generates the dark brown product MnO2, potassium permanganate rapidly stains virtually any organic material such as skin, paper, and clothing. Solid KMnO4 is a strong oxidizer and thus should be kept separated from oxidizable substances. Reaction with concentrated sulfuric acid produces the highly explosive manganese(VII) oxide (Mn2O7). When solid KMnO4 is mixed with pure glycerol or other simple alcohols it will result in a violent combustion reaction.

3 C3H5(OH)3 + 14 KMnO4 → 14 MnO2 + 7 K2CO3 + 2 CO2 + 12 H2O

References[edit]

  1. ^ Burriel, F.; Lucena, F.; Arribas, S. and Hernández, J. (1985), Química Analítica Cualitativa, p. 688, ISBN 84-9732-140-5.
  2. ^ a b c d Reidies, Arno H. (2002) "Manganese Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_123
  3. ^ Weeks, M. E. and Leicester, H. M.; Discovery of the Elements, Journal of Chemical Education 1968
  4. ^ "Important Trade Mark Case". Otago Witness 2 (2420): 53. 2 August 1900. 
  5. ^ Walton, H. F. (1948) Inorganic Preparations. New York.
  6. ^ "Handbook of Preparative Inorganic Chemistry"; Brauer, E., Ed.; Academic: New York, 1963
  7. ^ Gus J. Palenik "Crystal structure of potassium permanganate" Inorg. Chem., 1967, volume 6, pp 503–507.doi:10.1021/ic50049a015
  8. ^ Donald G. Lee, Shannon E. Lamb, and Victor S. Chang (1990), "Carboxylic Acids from the Oxidation of Terminal Alkenes by Permanganate: Nonadecanoic Acid", Org. Synth. ; Coll. Vol. 7: 397 
  9. ^ Ruhoff, John R., "n-Heptanoic acid", Org. Synth. ; Coll. Vol. 2: 315 
  10. ^ Gardner KA, Mayer JM (1995). "Understanding C-H Bond Oxidations: H· and H- Transfer in the Oxidation of Toluene by Permanganate". Science 269 (5232): 1849–51. doi:10.1126/science.7569922. PMID 7569922. 
  11. ^ a b Gillis, Bob and Labiste, Dino. "Fire by Chemical Reaction". 
  12. ^ Arthur W. Herriott (1977). "Purple benzene: Solubilization of anions in organic solvents". J. Chem. Educ. 54 (4): 229. doi:10.1021/ed054p229.1. 
  13. ^ Doheny, Anthony J., Jr. and Ganem, Bruce (1980). "Purple benzene revisited". J. Chem. Educ. 57 (4): 308. doi:10.1021/ed057p308.1. 
  14. ^ Cotton, F. A.; Wilkinson, G.; Murillo, C. A. and Bochmann, M. (1999). Advanced Inorganic Chemistry, 6th Edition. Wiley-VCH. ISBN 0-471-19957-5
  15. ^ Barthel, H. and Duvinage, B. (2000). "Clemens Winkler. His Experiments with Ozone in 1892". Praxis der Naturwissenschaften, Chemie 49: 18ff. 
  16. ^ Dzhabiev, T. S.; Denisov, N. N.; Moiseev, D. N. and Shilov, A. E. (2005). "Formation of Ozone During the Reduction of Potassium Permanganate in Sulfuric Acid Solutions". Russian Journal of Physical Chemistry 79: 1755–1760. 
  17. ^ Brody, Ester (February 2000). "Victor DeLor contractor profile". PaintPRO 2 (1). Retrieved 2009-11-12. "One of the techniques DeLor is known for among designers and clients is the special effects he creates with various chemical solutions. When applied to wood surfaces, these chemicals give a weathered appearance to new wood. ... To achieve the aesthetic on interior surfaces, DeLor often uses a mixture of water and potassium permanganate, a dry powder chemical." 
  18. ^ BIRT AR (March 1964). "Drugs for eczema of children". Can Med Assoc J 90 (11): 693–4. PMC 1922428. PMID 14127384. 
  19. ^ Stalder JF, Fleury M, Sourisse M, Allavoine T, Chalamet C, Brosset P, Litoux P (1992). "Comparative effects of two topical antiseptics (chlorhexidine vs KMnO4) on bacterial skin flora in atopic dermatitis". Acta Derm Venereol Suppl (Stockh) 176: 132–4. PMID 1476027. 
  20. ^ Program for Appropriate Technology in Health PATH (1988). "Skin diseases". Health Technol Dir 8 (3): 1–10. PMID 12282068. 
  21. ^ Assembly of Life Sciences (U.S.). Safe Drinking Water Committee (1977). Drinking water and health, Volume 2. National Academies Press. p. 98. ISBN 978-0-309-02931-5. 
  22. ^ Downey, Robyn and Barrington, Mike (28 February 2005) "Red faces over pink water", The Northern Advocate.
  23. ^ EPA Guidance Manual Alternative Disinfectants and Oxidants. epa.gov
  24. ^ Fatiadi, A. (1987). "The Classical Permanganate Ion: Still a Novel Oxidant in Organic Chemistry". Synthesis 1987 (2): 85–127. doi:10.1055/s-1987-27859. 
  25. ^ Kovacs KA, Grof P, Burai L, Riedel M (2004). "Revising the Mechanism of the Permanganate/Oxalate Reaction". J. Phys. Chem. A 108 (50): 11026. doi:10.1021/jp047061u. 
  26. ^ Code of Federal Regulations(7-1-07) Edition, Title 40, Part 60, Appendix A-8, Method 29, Section 7.3.1
  27. ^ van Rijswijk MH, van Heusden CW (1979). "The potassium permanganate method. A reliable method for differentiating amyloid AA from other forms of amyloid in routine laboratory practice". Am. J. Pathol. 97 (1): 43–58. PMC 2042379. PMID 495695. 
  28. ^ Picken, MM. (Apr 2010). "Amyloidosis-where are we now and where are we heading?". Arch Pathol Lab Med 134 (4): 545–51. doi:10.1043/1543-2165-134.4.545. PMID 20367306. 
  29. ^ Murphy CL, Eulitz M, Hrncic R, Sletten K, Westermark P, Williams T, Macy SD, Wooliver C, Wall J, Weiss DT, Solomon A (2001). "Chemical typing of amyloid protein contained in formalin-fixed paraffin-embedded biopsy specimens". Am. J. Clin. Pathol. 116 (1): 135–42. doi:10.1309/TWBM-8L4E-VK22-FRH5. PMID 11447744. 
  30. ^ Scott, KJ, McGlasson WB and Roberts EA (1970). "Potassium Permanganate as an Ethylene Absorbent in Polyethylene Bags to Delay the Ripening of Bananas During Storage". Australian Journal of Experimental Agriculture and Animal Husbandry 10 (43): 237. doi:10.1071/EA9700237. 
  31. ^ Scott KJ, Blake, JR, Stracha, G, Tugwell, BL and McGlasson WB (1971). "Transport of Bananas at Ambient Temperatures using Polyethylene Bags". Tropical Agriculture (Trinidad) 48: 163–165. 
  32. ^ Scott, KJ and Gandanegara, S (1974). "Effect of Temperature on the Storage Life of bananas Held in Polyethylene Bags with an Ethylene Absorbent". Tropical Agriculture (Trinidad) 51: 23–26. 
  33. ^ "Distress Signals". Evening Post CXXI (107): 5. 7 May 1936. 

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