Difference between revisions of "Potassium permanganate"

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[[File:Kmno4.jpg|thumb|Different sizes of potassium permanganate crystals.]]
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'''Potassium permanganate''' is an ionic compound with the formula KMnO<sub>4</sub>.''' '''At room temperature and pressure it is a deep violet crystalline salt that dissolves to form an intense violet or magenta solution, often tending to black in high concentrations. Potassium permanganate contains [[manganese]] in the +7 oxidation state, and is a strong [[oxidizer]] commonly encountered in a lab setting. It participates in a wide range of reactions, from simple colour change demonstrations to complex [[Organic synthesis|organic syntheses]].
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| Name = Potassium permanganate
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| Reference =
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| IUPACName = Potassium manganate(VII)
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| PIN =
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| SystematicName =
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| OtherNames = Chameleon mineral<br>Condy's crystals<br>Hypermangan<br>Permanganate of potash
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| ImageCaption = Different sizes of potassium permanganate crystals.
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| Section1 = {{Chembox Identifiers
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| Section2 = {{Chembox Properties
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| AtmosphericOHRateConstant =
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| Appearance = Dark purple crystals
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| BoilingPt =
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| BoilingPtC =
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| BoilingPt_ref =
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| BoilingPt_notes = Decomposes
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| Density = 2.703 g/cm<sup>3</sup> (25 °C)
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| Formula = KMnO<sub>4</sub>
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| HenryConstant =
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| LogP =
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| MolarMass = 158.034 g/mol
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| MeltingPt =
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| MeltingPtC = 240
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| MeltingPt_ref =
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| MeltingPt_notes = (decomposes)
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| Odor = Odorless
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| pKa =
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| pKb =
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| Solubility = 6.4 g/100 ml (20 °C)<br>25 g/100 ml (65 °C)
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| SolubleOther = Reacts with acids, [[alcohol]]s, [[glycerol]], halogens<br>Soluble in glacial [[acetic acid]], anhydrous [[acetonitrile]], [[benzonitrile]], [[pyridine]], [[sulfolane]], [[trifluoroacetic acid]]<br>Insoluble in hydrocarbons, halocarbons
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| Solubility1 = 1.02 g/100 ml
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| Solvent1 = bromoacetic acid
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| VaporPressure = ~ 0 mmHg
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| CrystalStruct = Orthorhombic
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| Section4 = {{Chembox Thermochemistry
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| DeltaGf = -713.8 kJ/mol
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| DeltaHc =
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| DeltaHf = −813.4 kJ/mol
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| Entropy = 171.7 J·mol<sup>-1</sup>·K<sup>-1</sup>
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| HeatCapacity = 119.2 J·mol<sup>-1</sup>·K<sup>-1</sup>
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| Section6 = {{Chembox Hazards
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| AutoignitionPt = Non-flammable
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| ExploLimits = Non-explosive
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| ExternalMSDS = [https://www.docdroid.net/XnxhJ5g/potassium-permanganate-sa.pdf.html Sigma-Aldrich]
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| FlashPt = Non-flammable
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| LD50 = 1,090 mg/kg (oral, rat)
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| LC50 =
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| MainHazards = Corrosive<br>Oxidizer
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| OtherCompounds = [[Potassium manganate]]
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'''Potassium permanganate''' is an ionic compound with the formula '''KMnO<sub>4</sub>'''. At room temperature and pressure it is a deep violet crystalline salt that dissolves to form an intense violet or magenta solution, often tending to black in high concentrations. Potassium permanganate contains [[manganese]] in the +7 oxidation state, and is a strong [[oxidizer]] commonly encountered in a lab setting. It participates in a wide range of reactions, from simple colour change demonstrations to complex [[Organic synthesis|organic syntheses]].
  
 
==Properties==
 
==Properties==
−
===Physical===
 
−
Potassium permanganate is a dark purple, almost black, crystalline solid that is soluble in water to form an intense magenta solution.
 
−
 
 
===Chemical===
 
===Chemical===
−
When exposed to light, potassium permanganate will [[Photodecomposition|photodecompose]] to form potassium manganate and manganese dioxide.
+
Potassium permanganate in the presence of strong acids will oxidize primary alcohols to carboxylic acids and secondary alcohols to ketones.
  
−
Concentrated [[Sulfuric acid|sulfuric acid]] dehydrates potassium permanganate to the incredibly unstable [[manganese heptoxide]]. Adding a few drops of [[glycerol]] (glycerin) to potassium permanganate creates an intense flame hot enough to light [[thermite]] and [[pyrotechnics]]. Addition of a dilute solution of [[sodium hydroxide]] and [[sucrose]] to [[potassium manganate]] solution and hydrous [[manganese dioxide]] creates a "chemical chameleon" reaction, in which the [[permanganate|permanganate ion]] is slowly reduced several times, producing several vivid color changes.
+
When exposed to strong light, potassium permanganate will break down to form potassium manganate and [[manganese dioxide]].
 +
 
 +
: 2 KMnO<sub>4</sub> → K<sub>2</sub>MnO<sub>4</sub> + MnO<sub>2</sub> + O<sub>2</sub>
 +
 
 +
Concentrated [[sulfuric acid]] dehydrates potassium permanganate to the incredibly unstable [[manganese heptoxide]].
 +
 
 +
: 2 KMnO<sub>4</sub> + 2 H<sub>2</sub>SO<sub>4</sub> → Mn<sub>2</sub>O<sub>7</sub> + KHSO<sub>4</sub> + H<sub>2</sub>O
 +
 
 +
Potassium permanganate reacts with concentrated [[hydrochloric acid]] to give chlorine and manganese(II) chloride:
 +
 
 +
: 2 KMnO<sub>4</sub> + 16 HCl<sub>2</sub> → 2 KCl + 2 MnCl<sub>2</sub> + 5 Cl<sub>2</sub> + 8 H<sub>2</sub>O
 +
 
 +
Adding a few drops of [[glycerol]] (glycerin) to potassium permanganate creates an intense flame hot enough to light [[thermite]] and [[pyrotechnics]]. Addition of a dilute solution of [[sodium hydroxide]] and [[sucrose]] to [[potassium manganate]] solution and hydrous [[manganese dioxide]] creates a "chemical chameleon" reaction, in which the [[permanganate|permanganate ion]] is slowly reduced several times, producing several vivid color changes.
  
 
In acidic solutions, permanganates reduce to manganese(II) ions. In neutral and mildly basic solutions, it reduces to manganese dioxide. In extremely basic solutions, the bluish-green manganate ion would form, but it would exist only transiently as it would be reduced to manganese dioxide.
 
In acidic solutions, permanganates reduce to manganese(II) ions. In neutral and mildly basic solutions, it reduces to manganese dioxide. In extremely basic solutions, the bluish-green manganate ion would form, but it would exist only transiently as it would be reduced to manganese dioxide.
 +
 +
===Physical===
 +
Potassium permanganate is a dark purple, almost black, crystalline solid that is soluble in water to form an intense magenta solution.
  
 
==Availability==
 
==Availability==
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Making permanganate is a difficult and messy exercise, and although extensive discussion on this topic has been undertaken on [[Sciencemadness Discussion Board|Sciencemadness]], a method that is accessible to the amateur but also produces worthwhile yields is still yet to be found.
 
Making permanganate is a difficult and messy exercise, and although extensive discussion on this topic has been undertaken on [[Sciencemadness Discussion Board|Sciencemadness]], a method that is accessible to the amateur but also produces worthwhile yields is still yet to be found.
  
−
The most popular method involves fusing a mixture of [[potassium nitrate]], [[potassium hydroxide]] and [[manganese dioxide]] to form crude [[potassium manganate]], then oxidizing it with the addition of a dilute solution of [[sodium bicarbonate]] (baking soda).
+
The most popular method involves fusing a mixture of [[potassium nitrate]], [[potassium hydroxide]] and [[manganese dioxide]] to form crude [[potassium manganate]], then disproportionating it (part of it oxidizes the other part, and is reduced as a result) to permanganate and manganese dioxide, with the addition of a dilute solution of [[sodium bicarbonate]] (baking soda). The yield of this route is poor, but the reagents are cheap.
 +
 
 +
A simple method involves fusing managnese dioxide, [[potassium chlorate]] and potassium hydroxide at around 400 °C for a while. Elemental chlorine is used to turn the manganate into permanganate. The yield of this route isn't great, but it's somewhat better than the previous ones mentioned.<ref>[https://www.youtube.com/watch?v=vmRE8zFAcRI Lab notes - Making Potassium Permanganate]</ref>
 +
 
 +
: 3 MnO<sub>2</sub> + 6 KOH + KClO<sub>3</sub> → 3 K<sub>2</sub>MnO<sub>4</sub> + KCl + 3 H<sub>2</sub>O
 +
: K<sub>2</sub>MnO<sub>4</sub> + ½ Cl<sub>2</sub> → KMnO<sub>4</sub> + KCl
 +
 
 +
==Projects==
 +
*Oxidize alcohols to carboxylic acids and ketones
 +
*Make [[benzoic acid]] from [[toluene]]
 +
*Convert alkenes into diols
 +
*Ignition of glycerol demonstration
 +
*Disinfectant
 +
*Age paper and wood
  
 
==Handling==
 
==Handling==
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While not overly toxic, potassium permanganate may strongly stain skin or other materials due to the formation of manganese dioxide when reacted with certain organics.
 
While not overly toxic, potassium permanganate may strongly stain skin or other materials due to the formation of manganese dioxide when reacted with certain organics.
  
−
Contact with concentrated [[sulphuric acid]] will create a very powerful, unpredictable and unstable oxidizer [[manganese heptoxide]]. Accidental creation of this must be avoided, and has been known to create disaster for the backyard chemist.
+
Contact with concentrated [[sulfuric acid]] will create a very powerful, unpredictable and unstable oxidizer [[manganese heptoxide]]. Accidental creation of this must be avoided, and has been known to create disaster for the backyard chemist.
  
 
Potassium permanganate vigorously reacts with many organic compounds, such as glycerol and [[ethylene glycol]], causing some to spontaneously combust. Appropriate care must be taken when combining the two in any setting.
 
Potassium permanganate vigorously reacts with many organic compounds, such as glycerol and [[ethylene glycol]], causing some to spontaneously combust. Appropriate care must be taken when combining the two in any setting.
  
 
===Storage===
 
===Storage===
−
Potassium permanganate should be stored in closed bottles, away from any acidic vapors or volatile organic compounds. KMnO<sub>4</sub> solutions should be covered as they will slowly break down in open air, due to dust or other chemical vapors.
+
Potassium permanganate should be stored in closed bottles, away from any acidic vapors or volatile organic compounds. KMnO<sub>4</sub> solutions should be covered as they will slowly break down in open air, due to dust or chemical vapors, generally organic.
  
 
===Disposal===
 
===Disposal===
−
Potassium permanganate can be neutralized with hydrogen peroxide, resulting [[potassium hydroxide]] and [[manganese dioxide]].
+
Potassium permanganate can be neutralized with [[hydrogen peroxide]], resulting [[potassium hydroxide]] and [[manganese dioxide]]. The latter can be recycled through sedimentation or filtration.
 +
 
 +
A mild reducing agent can also be used.
 +
 
 +
==Gallery==
 +
<gallery widths="220" position="center" columns="4" orientation="none">
 +
Potassium_permanganate.jpg|Crystals of potassium permanganate
 +
</gallery>
  
 
==References==
 
==References==
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===Relevant Sciencemadness threads===
 
===Relevant Sciencemadness threads===
 
*[http://www.sciencemadness.org/talk/viewthread.php?tid=8480 Permanganates]
 
*[http://www.sciencemadness.org/talk/viewthread.php?tid=8480 Permanganates]
 +
*[http://www.sciencemadness.org/talk/viewthread.php?tid=159613 Potassium permanganate from manganese dioxide, potassium hydroxide and potassium chlorate (as oxidising agent).]
 
*[http://www.sciencemadness.org/talk/viewthread.php?tid=3091 Potassium Permanganate Decomposition Products]
 
*[http://www.sciencemadness.org/talk/viewthread.php?tid=3091 Potassium Permanganate Decomposition Products]
 
*[http://www.sciencemadness.org/talk/viewthread.php?tid=4251 What do to with KMnO4?]
 
*[http://www.sciencemadness.org/talk/viewthread.php?tid=4251 What do to with KMnO4?]
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[[Category:Inorganic compounds]]
 
[[Category:Inorganic compounds]]
 
[[Category:Potassium compounds]]
 
[[Category:Potassium compounds]]
 +
[[Category:Manganese compounds]]
 
[[Category:Permanganates]]
 
[[Category:Permanganates]]
 
[[Category:Oxidizing agents]]
 
[[Category:Oxidizing agents]]
 
[[Category:DEA List II chemicals]]
 
[[Category:DEA List II chemicals]]
−
[[Category:Manganese compounds]]
 

Latest revision as of 21:27, 21 September 2023

Potassium permanganate
Kmno4.jpg
Different sizes of potassium permanganate crystals.
Names
IUPAC name
Potassium manganate(VII)
Other names
Chameleon mineral
Condy's crystals
Hypermangan
Permanganate of potash
Properties
KMnO4
Molar mass 158.034 g/mol
Appearance Dark purple crystals
Odor Odorless
Density 2.703 g/cm3 (25 °C)
Melting point 240 °C (464 °F; 513 K) (decomposes)
Boiling point Decomposes
6.4 g/100 ml (20 °C)
25 g/100 ml (65 °C)
Solubility Reacts with acids, alcohols, glycerol, halogens
Soluble in glacial acetic acid, anhydrous acetonitrile, benzonitrile, pyridine, sulfolane, trifluoroacetic acid
Insoluble in hydrocarbons, halocarbons
Solubility in bromoacetic acid 1.02 g/100 ml
Vapor pressure ~ 0 mmHg
Thermochemistry
171.7 J·mol-1·K-1
−813.4 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
1,090 mg/kg (oral, rat)
Related compounds
Related compounds
 Potassium manganate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium permanganate is an ionic compound with the formula KMnO4. At room temperature and pressure it is a deep violet crystalline salt that dissolves to form an intense violet or magenta solution, often tending to black in high concentrations. Potassium permanganate contains manganese in the +7 oxidation state, and is a strong oxidizer commonly encountered in a lab setting. It participates in a wide range of reactions, from simple colour change demonstrations to complex organic syntheses.

Properties

Chemical

Potassium permanganate in the presence of strong acids will oxidize primary alcohols to carboxylic acids and secondary alcohols to ketones.

When exposed to strong light, potassium permanganate will break down to form potassium manganate and manganese dioxide.

2 KMnO4 → K2MnO4 + MnO2 + O2

Concentrated sulfuric acid dehydrates potassium permanganate to the incredibly unstable manganese heptoxide.

2 KMnO4 + 2 H2SO4 → Mn2O7 + KHSO4 + H2O

Potassium permanganate reacts with concentrated hydrochloric acid to give chlorine and manganese(II) chloride:

2 KMnO4 + 16 HCl2 → 2 KCl + 2 MnCl2 + 5 Cl2 + 8 H2O

Adding a few drops of glycerol (glycerin) to potassium permanganate creates an intense flame hot enough to light thermite and pyrotechnics. Addition of a dilute solution of sodium hydroxide and sucrose to potassium manganate solution and hydrous manganese dioxide creates a "chemical chameleon" reaction, in which the permanganate ion is slowly reduced several times, producing several vivid color changes.

In acidic solutions, permanganates reduce to manganese(II) ions. In neutral and mildly basic solutions, it reduces to manganese dioxide. In extremely basic solutions, the bluish-green manganate ion would form, but it would exist only transiently as it would be reduced to manganese dioxide.

Physical

Potassium permanganate is a dark purple, almost black, crystalline solid that is soluble in water to form an intense magenta solution.

Availability

Like many chemicals, potassium permanganate was easier to find a few years ago, moderately difficult to find today and most likely getting harder and harder to locate in the next few years. It is sometimes sold as a camping chemical because it can light hot fires (when combined with glycerin), decontaminate water and disinfect wounds. Today it is easiest to find potassium permanganate at pharmacies/chemists or in aquarium supply stores as a type of water treatment.

Legality

The sale of potassium permanganate is regulated in several countries, due to its use in cocaine purification and methcathinone production. Check the local laws before using this substance.

Preparation

Making permanganate is a difficult and messy exercise, and although extensive discussion on this topic has been undertaken on Sciencemadness, a method that is accessible to the amateur but also produces worthwhile yields is still yet to be found.

The most popular method involves fusing a mixture of potassium nitrate, potassium hydroxide and manganese dioxide to form crude potassium manganate, then disproportionating it (part of it oxidizes the other part, and is reduced as a result) to permanganate and manganese dioxide, with the addition of a dilute solution of sodium bicarbonate (baking soda). The yield of this route is poor, but the reagents are cheap.

A simple method involves fusing managnese dioxide, potassium chlorate and potassium hydroxide at around 400 °C for a while. Elemental chlorine is used to turn the manganate into permanganate. The yield of this route isn't great, but it's somewhat better than the previous ones mentioned.[1]

3 MnO2 + 6 KOH + KClO3 → 3 K2MnO4 + KCl + 3 H2O
K2MnO4 + ½ Cl2 → KMnO4 + KCl

Projects

  • Oxidize alcohols to carboxylic acids and ketones
  • Make benzoic acid from toluene
  • Convert alkenes into diols
  • Ignition of glycerol demonstration
  • Disinfectant
  • Age paper and wood

Handling

Safety

While not overly toxic, potassium permanganate may strongly stain skin or other materials due to the formation of manganese dioxide when reacted with certain organics.

Contact with concentrated sulfuric acid will create a very powerful, unpredictable and unstable oxidizer manganese heptoxide. Accidental creation of this must be avoided, and has been known to create disaster for the backyard chemist.

Potassium permanganate vigorously reacts with many organic compounds, such as glycerol and ethylene glycol, causing some to spontaneously combust. Appropriate care must be taken when combining the two in any setting.

Storage

Potassium permanganate should be stored in closed bottles, away from any acidic vapors or volatile organic compounds. KMnO4 solutions should be covered as they will slowly break down in open air, due to dust or chemical vapors, generally organic.

Disposal

Potassium permanganate can be neutralized with hydrogen peroxide, resulting potassium hydroxide and manganese dioxide. The latter can be recycled through sedimentation or filtration.

A mild reducing agent can also be used.

Gallery

  • Crystals of potassium permanganate

References

  1. ↑ Lab notes - Making Potassium Permanganate

Relevant Sciencemadness threads

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