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Potassium persulfate

(Redirected from E922)
Not to be confused with Potassium peroxymonosulfate.

Potassium persulfate is the inorganic compound with the formula K2S2O8. Also known as potassium peroxydisulfate, it is a white solid that is sparingly soluble in cold water, but dissolves better in warm water. This salt is a powerful oxidant, commonly used to initiate polymerizations.

Potassium persulfate
Two potassium cations and one peroxydisulfate anion
Ball-and-stick model of the crystal structure
Potassium persulfate as a white powder
Names
Other names
  • potassium peroxydisulfate
  • Anthion
  • potassium perdisulfate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.028.893 Edit this at Wikidata
EC Number
  • 231-781-8
E number E922 (glazing agents, ...)
RTECS number
  • SE0400000
UNII
UN number 1492
  • InChI=1S/2K.H2O8S2/c;;1-9(2,3)7-8-10(4,5)6/h;;(H,1,2,3)(H,4,5,6)/q2*+1;/p-2 ☒N
    Key: USHAGKDGDHPEEY-UHFFFAOYSA-L ☒N
  • InChI=1/2K.H2O8S2/c;;1-9(2,3)7-8-10(4,5)6/h;;(H,1,2,3)(H,4,5,6)/q2*+1;/p-2
    Key: USHAGKDGDHPEEY-NUQVWONBAA
  • [O-]S(=O)(=O)OOS(=O)(=O)[O-].[K+].[K+]
Properties
K2S2O8
Molar mass 270.322 g/mol
Appearance white powder
Odor odorless
Density 2.477 g/cm3[1]
Melting point < 100 °C (212 °F; 373 K) (decomposes)
1.75 g/100 mL (0 °C)
4.49 g/100 mL (20 °C)
Solubility insoluble in alcohol
1.467
Structure
triclinic
Hazards
GHS labelling:
GHS03: Oxidizing GHS07: Exclamation mark GHS08: Health hazard
Danger
H272, H302, H315, H317, H319, H334, H335, H371
P220, P261, P280, P305+P351+P338, P342+P311
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
2
0
1
OX
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
802 mg/kg (oral, rat)[2]
Safety data sheet (SDS) ICSC 1133
Related compounds
Other anions
 Potassium sulfite
Potassium sulfate
Potassium peroxymonosulfate
Other cations
 Sodium persulfate
Ammonium persulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure

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The sodium and potassium salts are very similar. In the potassium salt, the O-O distance is 1.495 Å. The individual sulfate groups are tetrahedral, with three short S-O distances near 1.43 and one long S-O bond at 1.65 Å.[3]

Preparation

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Potassium persulfate can be prepared by electrolysis of a cold solution potassium bisulfate in sulfuric acid at a high current density.[1][4]

2 KHSO4 → K2S2O8 + H2

It can also be prepared by adding potassium bisulfate (KHSO4) to a solution of the more soluble salt ammonium peroxydisulfate (NH4)2S2O8. In principle it can be prepared by chemical oxidation of potassium sulfate using fluorine. Several million kilograms of the ammonium, sodium, and potassium salts of peroxydisulfate are produced annually.

Uses

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This salt is used to initiate polymerization of various alkenes leading to commercially important polymers such as styrene-butadiene rubber and polytetrafluoroethylene and related materials. In solution, the dianion dissociates to give radicals:[5]

[O3SO-OSO3]2− ⇌ 2 [SO4]•−

It is used in organic chemistry as an oxidizing agent,[6] for instance in the Elbs persulfate oxidation of phenols and the Boyland–Sims oxidation of anilines.

As a strong yet stable bleaching agent it also finds use in various hair bleaches and lighteners. Such brief and non-continuous use is normally hazard free, however prolonged contact can cause skin irritation.[7] It has been used as an improving agent for flour with the E number E922, although it is no longer approved for this use within the EU.

Precautions

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The salt is a strong oxidant and is incompatible with organic compounds. Prolonged skin contact can result in irritation.[7]

References

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  1. ^ a b Brauer, Georg (1963). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). New York: Academic Press. p. 392. ISBN 978-0121266011.
  2. ^ Chambers, Michael. "ChemIDplus - 7727-21-1 - USHAGKDGDHPEEY-UHFFFAOYSA-L - Potassium persulfate". chem.nlm.nih.gov.
  3. ^ Naumov, D.Yu.; Virovets, A.V.; Podberezskaya, N.V.; Novikov, P.B.; Politov, A.A. (1997). "Redetermination of the Crystal Structure of Potassium Peroxodisulfate (K2S2O8)". Zhurnal Strukturnoi Khimii. 38: 922-929.
  4. ^ Girolami, G. S.; Rauchfuss, T. B.; Angelici, R. J. (1999). Synthesis and Technique in Inorganic Chemistry. Mill Valley, CA: University Science Books. ISBN 0935702482.
  5. ^ Harald Jakob; Stefan Leininger; Thomas Lehmann; Sylvia Jacobi; Sven Gutewort. "Peroxo Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_177.pub2. ISBN 978-3527306732.
  6. ^ Encyclopedia of Reagents for Organic Synthesis, vol. 1, pp. 193–197(1995)
  7. ^ a b Pang, S; Fiume, MZ (January 2001). "Final Report on the Safety Assessment of Ammonium, Potassium, and Sodium Persulfate". International Journal of Toxicology. 20 (3): 7–21. doi:10.1080/10915810152630710. PMID 11766134. S2CID 25763799.
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