Sodium metabisulfite

Sodium metabisulfite

Names
Other names Sodium pyrosulfite Sodium disulfite
Identifiers
CAS Number	7681-57-4 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:114786 N
ChEMBL	ChEMBL2016976 N
ECHA InfoCard	100.028.794
EC Number	231-673-0
E number	E223 (preservatives)
PubChem	656671
RTECS number	UX8225000
InChI InChI=1S/2Na.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2
SMILES [O-]S(=O)S(=O)(=O)[O-].[Na+].[Na+]
Properties
Chemical formula	Na2S2O5, Na-O-(S=O)-O-(S=O)-O-Na
Molar mass	190.107 g/mol
Appearance	white to yellow powder
Odor	faint SO2
Density	1.48 g/cm3
Melting point	170 °C (338 °F; 443 K) decomposition begins at 150 °C
Solubility in water	45.1 g/100 mL (0 °C) 65.3 g/100 mL (20 °C) 81.7 g/100 mL (100 °C)
Solubility	very soluble in glycerol soluble in ethanol
Hazards
Safety data sheet	Mallinckrodt MSDS
EU classification (DSD)	Harmful (Xn) Irritant (Xi)
R-phrases	R22 R31 R41
S-phrases	(S2) S26 S39 S46
NFPA 704	0 2 1
US health exposure limits (NIOSH):
PEL (Permissible)	none
REL (Recommended)	TWA 5 mg/m3
IDLH (Immediate danger)	N.D.
Related compounds
Other anions	Sodium sulfite Sodium bisulfite
Other cations	Potassium metabisulfite
Related compounds	Sodium dithionite Sodium thiosulfate Sodium sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na₂S₂O₅. The substance is sometimes referred to as disodium (metabisulfite). It is used as a disinfectant, antioxidant and preservative agent.

Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide:

which leaves solid Na₂S₂O₅ behind.

The anion metabisulfite is a hybrid of dithionite (S₂O₄²⁻) and dithionate (S₂O₆²⁻). The anion consists of an SO₂ group linked to an SO₃ group, with the negative charge more localized on the SO₃ end. The S–S bond length is 2.22 Å, and the "thionate" and "thionite" S–O distances are 1.46 and 1.50 Å respectively.

It is used as a preservative and antioxidant in food and is also known as E223.

It may cause allergic reactions in those who are sensitive to sulfites, including respiratory reactions in asthmatics, anaphylaxis and other allergic reactions in sensitive individuals.

Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.

The acceptable daily intake is up to 0.7 milligrams per kilogram of body weight. Sodium metabisulfite oxidizes in the liver to sulfate which is excreted in the urine.

It is commonly used in homebrewing and winemaking to sanitize equipment. It is used as a cleaning agent for potable water reverse osmosis membranes in desalination systems. It is also used to remove chloramine from drinking water after treatment.