Potassium persulfate

Potassium persulfate is the inorganic compound with the formula K2S2O8. Also known as potassium peroxydisulfate or KPS, 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.

Not to be confused with Potassium peroxymonosulfate.
Potassium persulfate
Names
Other names
potassium peroxydisulfate
Anthion
potassium perdisulfate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.028.893
EC Number
  • 231-781-8
E number E922 (glazing agents, ...)
RTECS number
  • SE0400000
UNII
UN number 1492
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
Safety data sheet ICSC 1133
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H272, H302, H315, H317, H319, H334, H335, H371
P220, P261, P280, P305+351+338, P342+311
NFPA 704 (fire diamond)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
802 mg/kg (oral, rat)[2]
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).
N verify (what is YN ?)
Infobox references

Preparation

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

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.

Uses

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:[3]

[O3SO-OSO3]2− ⇌ 2 [SO4]•−

It is used in organic chemistry as an oxidizing agent,[4] 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.[5] 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

The salt is a strong oxidant and is incompatible with organic compounds. Prolonged skin contact can result in irritation.[5]

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References
  1. Brauer, Georg (1963). Handbook of Preparative Inorganic Chemistry. 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. 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.
  4. Encyclopedia of Reagents for Organic Synthesis, vol. 1, pp. 193–197(1995)
  5. 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.
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