Potassium persulfate

Potassium persulfate

Names
Other names potassium peroxydisulfate Anthion potassium perdisulfate
Identifiers
CAS Number	7727-21-1
3D model (Jmol)	Interactive image
ChemSpider	22821
ECHA InfoCard	100.028.893
EC Number	231-781-8
E number	E922 (glazing agents, ...)
PubChem	24412
RTECS number	SE0400000
UN number	1492
InChI 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 Key: USHAGKDGDHPEEY-UHFFFAOYSA-L 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
SMILES [O-]S(=O)(=O)OOS(=O)(=O)[O-].[K+].[K+]
Properties
Chemical formula	K2S2O8
Molar mass	270.322 g/mol
Appearance	white powder
Odor	odorless
Density	2.477 g/cm^3[1]
Melting point	< 100 °C (212 °F; 373 K) (decomposes)
Solubility in water	1.75 g/100 mL (0 °C) 4.49 g/100 ml (20 °C)
Solubility	insoluble in alcohol
Refractive index (nD)	1.467
Structure
Crystal structure	triclinic
Hazards
Safety data sheet	ICSC 1133
EU classification (DSD)	Oxidant (O) Harmful (Xn) Irritant (Xi)
R-phrases	R8, R22, R36/37/38, R42/43
S-phrases	(S2), S22, S24, S26, S37
NFPA 704	0 2 1 OX
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	802 mg/kg (oral, rat)[2]
Related compounds
Other anions	Potassium sulfite Potassium sulfate Potassium peroxymonosulfate
Other cations	Sodium 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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Infobox references

Not to be confused with potassium peroxymonosulfate.

Potassium persulfate is the inorganic compound with the formula K₂S₂O₈. Also known as potassium peroxydisulfate or KPS, it is a white solid that is highly soluble in water. This salt is a powerful oxidant, commonly used to initiate polymerizations.

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 polymerziation 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]

References

1. Brauer, Georg (1963). Handbook of Preparative Inorganic Chemistry Vol. 1, 2nd Ed. Newyork: Academic Press. p. 392. ISBN 978-0121266011.
2. http://chem.sis.nlm.nih.gov/chemidplus/rn/7727-21-1
3. Harald Jakob, Stefan Leininger, Thomas Lehmann, Sylvia Jacobi, Sven Gutewort (2005), "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. "Final Report on the Safety Assessment of Ammonium, Potassium, and Sodium Persulfate". International Journal of Toxicology. 20 (3): 7-21. January 2001. doi:10.1080/10915810152630710.