Potassium disulfite

Structural formula
General
Surname	Potassium disulfite
other names	Potassium metabisulfite Potassium pyrosulfite E  224 POTASSIUM METABISULFITE ( INCI )
Molecular formula	K 2 S 2 O 5
Brief description	white solid with a faint odor
External identifiers / databases
CAS number 16731-55-8 EC number 240-795-3 ECHA InfoCard 100,037,072 PubChem 28019 ChemSpider 26061 Wikidata Q417881
properties
Molar mass	222,33 g · mol -1
Physical state	firmly
density	2.34 g cm −3 (20 ° C)
Melting point	Decomposition from 150 ° C
solubility	easy in water (450 g l −1 at 20 ° C) insoluble in alcohol
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 318-335 EUH: 031 P: 280-305 + 351 + 338-313
Toxicological data	2300 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium disulfite (K ₂ S ₂ O ₅ ) also known as potassium metabisulfite , potassium pyrosulfite or commonly known as dumpling white and onewe , is a potassium salt of disulfurous acid , which is not stable in its free form . Disulfites have a very long, unstable sulfur- sulfur bond. Potassium disulfite is mainly used as a food additive (E 224). Under acidic conditions, the compound splits off sulfur dioxide :

${\displaystyle \mathrm {K_{2}S_{2}O_{5}\ +\ 2\ HCl\ \rightarrow \ 2\ KCl\ +\ 2\ SO_{2}\ +\ H_{2}O} }$

Extraction and presentation

It is produced by thermal dimerization ( condensation ) of potassium hydrogen sulfite with the elimination of water (1), or when sulfur dioxide and potassium sulfite are converted into potassium hydroxide (2):

(1) ${\displaystyle \mathrm {2\ HSO_{3}^{-}\rightarrow \ H_{2}O\ +\ S_{2}O_{5}^{2-}} }$

(2) ${\displaystyle \mathrm {SO_{3}^{2-}\ +\ SO_{2}\ \rightarrow \ S_{2}O_{5}^{2-}} }$

use

The food additive potassium disulphite (E 224) is used as a preservative , antioxidant and color stabilizer in food (e.g. also in the sulphurisation of wine ). Potassium disulfite is also known as dumpling white. It prevents the dumplings from turning gray during processing.

It is also generally used as a reducing agent in the chemical industry, for bleaching sugar, as an etching agent in the electronics industry and as a component of fixing agents in the photo industry.

Together with potassium peroxodisulphate , it can be used as a free radical starter in emulsion polymerisation because, in contrast to other common initiators such as dibenzoyl peroxide (DBPO) and azobis (isobutyronitrile) (AIBN), it is soluble in the main medium used, water.

Individual evidence

1. ↑ Entry on E 224: Potassium metabisulphite in the European database for food additives, accessed on June 27, 2020.
2. ↑ Entry on POTASSIUM METABISULFITE in the CosIng database of the EU Commission, accessed on February 25, 2020.
3. ↑ ^{a b c d e f} Entry on potassium disulphite in the GESTIS substance database of the IFA , accessed on July 23, 2016(JavaScript required) .
4. ↑ BASF: Potassium disulfite types
5. ↑ Data sheet potassium disulfite (PDF) from Merck , accessed on January 18, 2011.
6. ↑ metallograf.de: List of chemicals for caustic agents , accessed on June 18, 2016.