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Potassium permanganate

 

Potassium permanganate

Potassium permanganate
Names
IUPAC name
Potassium manganate(VII)
Other names
Potassium permanganate
Chameleon mineral
Condy's crystals
Permanganate of potash
Hypermangan
Identifiers
 Y
ATC code D08
V03
ChemSpider  Y
EC number 231-760-3
Jmol-3D images Image
KEGG  N
PubChem
RTECS number SD6475000
UN number 1490
Properties
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)
6.4 g/100mL (20 °C)
250 g/L (65 °C)
Solubility decomposes in organic solvents
1.59
Structure
Orthorhombic
Thermochemistry
119.2 J/mol K
171.7 J K−1 mol−1
−813.4 kJ/mol
-713.8 kJ/mol
Hazards
Oxidizing Agent O (O)
Harmful Xn (Xn)
Dangerous for the Environment (Nature) N (N)
R-phrases R50/53
S-phrases (S2), S60, S61
NFPA 704
0
2
0
OX
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
1090 mg/kg (oral, rat)[1]
Related compounds
Other anions
Potassium manganite
Potassium manganate
Other cations
Sodium permanganate
Ammonium permanganate
Related compounds
Manganese heptoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 N  (: Y/N?)

Potassium permanganate is an chemical 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.[2] In 2000, worldwide production was estimated at 30,000 tonnes.[3] In this compound, manganese is in the +7 oxidation state.

Contents

  • History 1
  • Preparation 2
    • Other methods 2.1
  • Structure 3
  • Reactions 4
    • Organic chemistry 4.1
    • Reaction with acids 4.2
    • Thermal decomposition 4.3
  • Uses 5
    • Water treatment and disinfection 5.1
    • Synthesis of organic compounds 5.2
    • Analytical use 5.3
    • Fruit preservation 5.4
    • Survival kits 5.5
    • Fire service 5.6
    • Other uses 5.7
  • Safety and handling 6
  • References 7
  • External links 8

History

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.[4] Just under 200 years later, London chemist Henry Bollmann Condy had an interest in disinfectants; he found that fusing pyrolusite with sodium hydroxide (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 potassium hydroxide (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 to stop competitors from marketing similar products.[5]

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.

Preparation

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 another source of oxygen, like potassium nitrate or potassium chlorate.[3] This process gives potassium manganate:

2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O

(Using sodium hydroxide the end product is not sodium manganate but an Mn(V) compound which is one reason the potassium permanganate is more commonly used than sodium permanganate. Furthermore the potassium salt crystallizes better[3]).

The potassium manganate is then converted into permanganate by electrolytic oxidation in alkaline media:

K2MnO4 + H2O → KMnO4 + KOH + 1/2 H2

Other methods

Although of no commercial importance, potassium manganate can be oxidized by chlorine or by disproportionation under acid conditions [6] The chlorine oxidation reaction is:

2 K2MnO4 + Cl2 → 2 KMnO4 + 2 KCl

And the acid-induced disproportionation reaction may be written:

3 K2MnO4 + 4 HCl → 2 KMnO4 + MnO2 + 2 H2O + 4 KCl

A weak acid such as carbonic acid is sufficient for this reaction:

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

Potassium permanganate crystallizes from the concentrated reaction solution.

Permanganate salts can also be generated by treating a solution of Mn2+ ions with strong oxidants such as Tests for the presence of manganese exploit the vivid violet color of permanganate produced by these reagents.

Structure

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.[7] In the solid (as in solution), each MnO4 centres are tetrahedral. The Mn-O distances are 1.62 Å.[8]

Reactions

Organic chemistry

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:[9]

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:[10]

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.[11]

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.[12] 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,[13] or by sequestering the potassium cation with a crown ether.[14]

Reaction with acids

Concentrated sulfuric acid reacts with KMnO4 to give Mn2O7, which can be explosive.[15] 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.[16][17]

Thermal decomposition

Solid potassium permanganate decomposes when heated:

2KMnO4 → K2MnO4 + MnO2(s) + O2

Uses

Almost all applications of potassium permanganate exploit its oxidizing properties.[3] As a strong oxidant that does not generate toxic byproducts, KMnO4 has many niche uses.

Water treatment and disinfection

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 Zebra mussels in fresh water collection and treatment systems.[23]

Synthesis of organic compounds

A solution of KMnO4 in water, in a volumetric flask

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.[3]

Analytical use

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 was used as a bleaching agent.[27][28]

Fruit preservation

Ethylene absorbents extend storage time of bananas even at high temperatures. This effect can be exploited by packing bananas in polyethylene together with potassium permanganate. By removing ethylene by oxidation, the permanganate delays the ripening., increasing the fruit's shelf life up to 4 weeks without the need for refrigeration.[29][30][31]

Survival kits

Potassium permanganate is typically included in survival kits: as a fire starter (mixed with antifreeze from a car radiator or glycerin),[12] water sterilizer, and for creating distress signals on snow.[32]

Fire service

Potassium permanganate is used in the "plastic sphere dispensers" used to set backfires, burnouts, and prescribed fires. Polymer spheres resembling ping-pong balls containing small amounts of permanganate are injected with ethylene glycol and projected towards the area where ignition is desired, where they spontaneously ignite seconds later.[33][34] Both handheld[34] and helicopter-[33] or boat-mounted[34] plastic sphere dispensers are used.

Other uses

Potassium permanganate is one of the principal chemicals used in the film and television industries to "age" props and set dressings. Its ready conversion to brown MnO2 create "hundred-year-old" or "ancient" looks on Hessian cloth, ropes, timber, and glass.[35]

Potassium permanganate has been used in attempts to induce abortions at home. These incidents only result in damage to the vagina from the corrosive action of the chemical, since potassium permanganate was proven to be ineffective in producing abortions. The FDA increased legal restrictions on the chemical in response to its use as an abortifacient.[36]

Safety and handling

As an oxidizer that generates the dark brown product manganese(VII) oxide (Mn2O7). When solid, KMnO4 mixed with pure glycerol or other simple alcohols will result in a violent combustion reaction.

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

References

  1. ^ http://chem.sis.nlm.nih.gov/chemidplus/rn/7722-64-7
  2. ^ Burriel, F.; Lucena, F.; Arribas, S. and Hernández, J. (1985), Química Analítica Cualitativa, p. 688, ISBN 84-9732-140-5.
  3. ^ a b c d e Reidies, Arno H. (2002) "Manganese Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_123
  4. ^ Weeks, M. E. and Leicester, H. M.; Discovery of the Elements, Journal of Chemical Education 1968
  5. ^ "Important Trade Mark Case". Otago Witness 2 (2420): 53. 2 August 1900. 
  6. ^ Walton, H. F. (1948) Inorganic Preparations. New York.
  7. ^ "Handbook of Preparative Inorganic Chemistry" Brauer, E., Ed.; Academic: New York, 1963
  8. ^ Palenik, Gus J. (1967). "Crystal structure of potassium permanganate". Inorg. Chem. 6 (3): 503–507.  
  9. ^ Donald G. Lee, Shannon E. Lamb, and Victor S. Chang (1990). "Carboxylic Acids from the Oxidation of Terminal Alkenes by Permanganate: Nonadecanoic Acid".  
  10. ^ Ruhoff, John R. -Heptanoic acid"n".  
  11. ^ 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.  
  12. ^ a b Gillis, Bob and Labiste, Dino. "Fire by Chemical Reaction". 
  13. ^ Arthur W. Herriott (1977). "Purple benzene: Solubilization of anions in organic solvents". J. Chem. Educ. 54 (4): 229.  
  14. ^ Doheny, Anthony J., Jr. and Ganem, Bruce (1980). "Purple benzene revisited". J. Chem. Educ. 57 (4): 308.  
  15. ^ Cotton, F. A.; Wilkinson, G.; Murillo, C. A. and Bochmann, M. (1999). Advanced Inorganic Chemistry, 6th Edition. Wiley-VCH. ISBN 0-471-19957-5
  16. ^ Barthel, H. and Duvinage, B. (2000). "Clemens Winkler. His Experiments with Ozone in 1892". Praxis der Naturwissenschaften, Chemie 49: 18ff. 
  17. ^ 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. 
  18. ^ BIRT AR (March 1964). "Drugs for eczema of children". Can Med Assoc J 90 (11): 693–4.  
  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.  
  20. ^ Program for Appropriate Technology in Health PATH (1988). "Skin diseases". Health Technol Dir 8 (3): 1–10.  
  21. ^ Assembly of Life Sciences (U.S.). Safe Drinking Water Committee (1977). Drinking water and health, Volume 2. National Academies Press. p. 98.  
  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".  
  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.  
  26. ^ Code of Federal Regulations(7-1-07) Edition, Title 40, Part 60, Appendix A-8, Method 29, Section 7.3.1
  27. ^ Picken, MM. (Apr 2010). "Amyloidosis-where are we now and where are we heading?". Arch Pathol Lab Med 134 (4): 545–51.  
  28. ^ 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.  
  29. ^ 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.  
  30. ^ 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. 
  31. ^ 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. 
  32. ^ "Distress Signals". Evening Post CXXI (107): 5. 7 May 1936. 
  33. ^ a b Plastic Sphere Dispenser - US Forest Service
  34. ^ a b c ""Wetland Warrior"".  
  35. ^ 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. 
  36. ^ "CFR - Code of Federal Regulations Title 21". U.S. Food and Drug Administration. U.S. Department of Health & Human Services. Retrieved 1 April 2015. 

External links

  • International Chemical Safety Card 0672
  • National Pollutant Inventory: Manganese and compounds Fact Sheet
  • The use of potassium permanganate in fish ponds
  • Sugar, NaOH and KMnO4
Crystallization of KMnO4 aqueous solution in real-time due to evaporation, 200x magnification
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