Potassium persulfate

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

Names
Other names potassium peroxydisulfate Anthion potassium perdisulfate
Identifiers
CAS Number	7727-21-1 Y
3D model (JSmol)	Interactive image
ChemSpider	22821 N
ECHA InfoCard	100.028.893
EC Number	231-781-8
E number	E922 (glazing agents, ...)
PubChem CID	24412
RTECS number	SE0400000
UNII	6B86K0MCZC Y
UN number	1492
CompTox Dashboard (EPA)	DTXSID4029690
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 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
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/cm3[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
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H272, H302, H315, H317, H319, H334, H335, H371
Precautionary statements	P220, P261, P280, P305+P351+P338, P342+P311
NFPA 704 (fire diamond)	2 0 1 OX
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	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). N verify (what is YN ?) Infobox references

Structure

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

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

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

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

References

1. 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. 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.