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Potassium permanganate

Drugs & Medication

Potassium permanganate

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Potassium permanganate
Potassium permanganate unit cellPotassium permanganate
General
Other names Potassium manganate(VII)
Molecular formula KMnO4
Molar mass 158.04 g/mol
Appearance black needles;

vivid purple in solution

CAS number [7722-64-7]
Properties
Density and phase 2.703 g/cm3, solid
Solubility in water 6.38 g/100 ml (20 °C)
Melting point 270 °C decomp.
Thermodynamic data
Standard enthalpy
of formation ΔfH°solid
−813.4 kJ/mol
Standard molar entropy
S°solid
171.7 J.K−1.mol−1
Hazards
EU classification Oxidant (O)
Harmful (Xn)
Dangerous for
the environment (N)
NFPA 704
0
1
0
OX
R-phrases R8, R22, R50/53
S-phrases S2, S60, S61
Related compounds
Other anions Potassium perrhenate
Other cations Sodium permanganate
Related compounds Potassium manganite
Potassium manganate
Manganese heptoxide
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)

Potassium permanganate is the chemical compound KMnO4. In this salt, manganese is in the +7 oxidation state. The salt is also known as "permanganate of potash" and "Condy's crystals". The permanganate ion is a strong oxidizing agent. It dissolves in water to give deep purple solutions, evaporation of which gives prismatic purple-black glistening crystals.[1] It has a sweet taste and is odourless. [2]

Contents

History

In 1659 a German chemist, J.R. Glauber, fused a mixture of the mineral pyrolusite and potassium carbonate to obtain a material that, when dissolved in water, gave a green solution (sodium manganate) which slowly changed colour to violet (potassium permanganate) and then finally red. This report represents the first description of the production of potassium permanganate.

Just under 200 years later a Londoner named Henry Bollmann Condy trained as a chemist. He had an interest in disinfectants and marketed a number of products including ozonised water. He found that when he fused pyrolusite with NaOH and dissolved the product in water it gave a solution that had good disinfectant properties. He patented this solution, and marketed it as Condy's Fluid. The problem was that the solution, although quite effective, was not very stable. This difficulty was overcome by using KOH rather than NaOH. This gave a more stable material, which had the added advantage of being easily converted 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.

Early photographers used it as a component of flash powder.

Uses

Chemical applications

Potassium permanganate is used as an oxidizing agent in diverse chemical reactions in the laboratory and in industry.[3] It also serves as a disinfectant and in deodorizers. It can be used as a reagent for the synthesis of many different kinds of chemical compounds. In wastewater treatment, it is used to neutralize hydrogen sulfide. In analytical chemistry, a standardized aqueous solution of KMnO4 is sometimes used as an oxidizing titrant for redox titrations due to its deep purple color. In a related way, it is used as a reagent to determine the Kappa number of wood pulp. Mixing potassium permanganate and formaldehyde forms a mild tear gas.

As an oxidant in organic synthesis

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 permanganate solution; thus it is sometimes referred to as Baeyer's reagent.

Concentrated solutions oxidize a methyl group on an aromatic ring, e.g. toluene to benzoic acid.

KMnO4 oxidizes pseudoephedrine hydrochloride to produce methcathinone, a Schedule I drug in the United States. Consequently the DEA has restricted its use and sale by classifying it as a List I controlled precursor. Potassium permanganate is listed as a Table I precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.[1]

Acids and KMnO4

diluted sulfuric acid reacts with KMnO4 to give Mn2O7, which can be explosive.[4][5][6]. Similarly concentrated HCl gives chlorine. The Mn-containing products from redox reactions depend on the pH. Acidic solutions of permanganate are reduced to the faintly pink [Mn(H2O)6]2+. In neutral solution, permanganate is only reduced by 5e- to give a soluton of Mn2+ (aq), wherein Mn is in a +2 oxidation state. This is the material that stains one's skin when handling KMnO4. KMnO4 spontaneously reduced in an alkaline solution to green-coloured K2MnO4, wherein manganese is in the +6 oxidation state.

A curious reaction is observed when one adds 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. An approximate equation for the ozone formation is shown below.

At room temperature
6 KMnO4(aq) + 9 H2SO4(aq) → 6 MnSO4(aq) + 3 K2SO4(aq) + 9 H2O(l) + 5 O3(g)

Biomedical uses

  • Dilute solutions are used as a treatment for canker sores (ulcers) (0.25%), disinfectant for the hands (about 1%) and treatment for mild pompholyx dermatitis or fungal infections of the hands or feet.
  • A dilute solution of acidified potassium permanganate is used in histology to bleach melanin which obscures tissue detail.
  • Potassium permanganate can be used to differentiate amyloid AA from other types of amyloid pathologically deposited in body tissues. Incubation of fixed tissue with potassium permanganate will prevent amyloid AA from staining with congo red whereas other types of amyloid are unaffected.[7][8]

Miscellaneous uses

A solution of KMnO4 in water, in a volumetric flask
A solution of KMnO4 in water, in a volumetric flask
  • 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 still used in torpedoes.
  • A dilute (10mg/l) of potassium permanganate can be used to eliminate snails from plants prior to placing them in a fresh-water aquarium.
  • High-grade potassium permanganate can be found at pool supply stores and is used in rural areas to remove iron and hydrogen sulfide (rotten egg smell) from well water.
  • KMnO4 is often included in survival kits along with either glycerine or a glucose tablet for the purposes of making fire. The glucose tablet can be ground up, mixed with the potassium permanganate and caused to combust by applying friction. It can also be mixed with anti-freeze from a vehicle to produce flame, although this can be dangerous and should be done in a controlled manner ie dipping some paper into the anti-freeze and then adding a small amount of potassium permanganate. The ability to sterilise water and wounds is also advantageous and another reason for inclusion in a survival kit.
  • KMnO4 is employed to treat some parasitic diseases of fish, in treatment of drinking water, as well as an antidote in phosphorus poisoning. In Africa, it has been used as a disinfectant for vegetables such as lettuce.

Hazards

Solid KMnO4 is a strong oxidizer and in general it should be kept separated from oxidisible substances. For more information consult an MSDS. Some reactions need a bit of a solvent, for example, powdered potassium permanganate + powdered sugar will ignite (but not explode) a few seconds after a drop of water is added. Dilute aqueous solutions of KMnO4 are not dangerous. KMnO4 forms dangerous products upon contact with concentrated acids.

Potassium permanganate stains the hand and clothing (as it is reduced to MnO2) and should be handled with care. Clothing stains may be washed away using acetic acid. Skin stains disappear within 48 hours.

References

  1.  F. Burriel, F. Lucena, S. Arribas and J. Hernández, (1985), Química Analítica Cualitativa, page 688, ISBN 84-9732-140-5.
  2.   Fatiadi, A. J. Synthesis 1987, 85-127. (Review) (DOI:10.1055/s-1987-27859)
  3.   F. A. Cotton, G. Wilkinson, C. A. Murillo, and M. Bochmann (April 1999). Advanced Inorganic Chemistry, 6th Edition. Wiley-VCH. ISBN 0-471-19957-5
  4.   van Rijswijk MH, van Heusden CW.American Journal of Pathology.1979Oct;97(1):43-58. PMID: 495695
  5.  Dzhabiev, T. S.; Denisov, N. N.; Moiseev, D. N. and Shilov, A. E., "Formation of Ozone During the Reduction of Potassium Permanganate in Sulfuric Acid Solutions", Russian Journal of Physical Chemistry, 2005, volume 79, pages 1755-1760.
  6.  Barthel, H. and Duvinage, B., "Clemens Winkler. His Experiments with Ozone in 1892", Praxis der Naturwissenschaften, Chemie, 2000, volume 49, page 18ff.
  7.  Wright JR, Calkins E, Humphrey RL.Laboratory Investigation. 1977 Mar;36(3):274-81. PMID: 839739
  1. ^ Red list

External links


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This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.


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