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^[1]
REL (Recommended)	TWA 5 mg/m³^[1]
IDLH (Immediate danger)	N.D.^[1]
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 verify (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.

Preparation

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

2 HSO₃⁻ ⇌ H₂O + S₂O₅²⁻

which leaves solid Na₂S₂O₅ behind.^[2]

Chemical structure

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.^[3]

Uses

Food additive

It is used as a preservative and antioxidant in food and is also known as E223.^[4]

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.^[5]^[6]

Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.^[7]

The acceptable daily intake is up to 0.7 milligrams per kilogram of body weight.^[8] Sodium metabisulfite oxidizes in the liver to sulfate which is excreted in the urine.^[8]

Sanitization and cleaning agent

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.

Other uses

Added to local anaesthetic (lidocaine etc.) solutions to prevent oxidation of vasoconstrictor adrenaline and thus improve the shelf life of the solution
It is used in photography.^[9]
Concentrated sodium metabisulfite can be used to remove tree stumps. Some brands contain 98% sodium metabisulfite, and cause degradation of lignin in the stumps, facilitating removal.^[10]
It is also used as an excipient in some tablets, such as paracetamol. Approximately 0.5 mg is used in epinephrine autoinjectors such as the EpiPen.
A very important health related aspect of this substance is that it can be added to a blood smear in a test for sickle cell anaemia (and other similar forms of haemoglobin mutation). The substances causes defunct cells to sickle (through a complex polymerisation) hence confirming disease.
It is used as the source of SO₂ in wine. An important anti-oxidant and bactericide
It is also used to precipitate gold from auric acid (gold dissolved in aqua regia).
It is used in waste treatment to chemically reduce hexavalent chromium to trivalent chromium which can then be precipitated and removed from an aqueous waste stream.
It is used as a bleaching agent in the production of Coconut cream
It is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibers, thus allowing the garment to go back to its original shape after washing
It is used as an SO₂ source (mixed with air or oxygen) for the destruction of cyanide in commercial gold cyanidation processes.
It is used in the oil and gas industry as a corrosion inhibitor/oxygen scavenger.
It is used in the water treatment industry to quench chlorine residual

Chemical properties

When mixed with water, sodium metabisulfite releases sulfur dioxide (SO₂), a pungent, unpleasant smelling gas that can also cause breathing difficulties in some people. For this reason, sodium metabisulfite has fallen from common use in recent times, with agents such as hydrogen peroxide becoming more popular for effective and odorless sterilization of equipment. Released sulfur dioxide however makes the water a strong reducing agent.

Sodium metabisulfite releases sulfur dioxide in contact with strong acids:

Na₂S₂O₅ + 2 HCl → 2 NaCl + H₂O + 2 SO₂

On heating to high temperature, it releases sulfur dioxide, leaving sodium sulfite behind:^[11]

Na₂S₂O₅ → Na₂SO₃ + SO₂

References

1 2 3 "NIOSH Pocket Guide to Chemical Hazards #0566". National Institute for Occupational Safety and Health (NIOSH).
↑ Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6.
↑ K. L. Carter, T. A. Siddiquee, K. L. Murphy, D. W. Bennett "The surprisingly elusive crystal structure of sodium metabisulfite" Acta Crystallogr. (2004). B60, 155–162. doi:10.1107/S0108768104003325
↑ "Food Additives approved by the EU" (PDF). Retrieved 12 March 2015.
↑ Dean D. Metcalfe, Ronald A. Simon, Food allergy: adverse reactions to food and food additives, Wiley-Blackwell 2003, p. 324–339
↑ http://www.ific.org/publications/brochures/asthmabroch.cfm
↑ Milne, George W. A. (2005). Gardner's commercially important chemicals: synonyms, trade names, and properties. New York: Wiley-Interscience. p. 568. ISBN 0-471-73518-3.
1 2 "Food-Info.net : E-numbers : E223: Sodium disulphite". food-info.net.
↑ Anchell, Steve (2008). The darkroom cookbook (3rd ed.). Amsterdam: Focal Press. p. 193. ISBN 0240810554.
↑ http://www.bonideproducts.com/lbonide/msds/msds271.pdf
↑ Sodium sulfite. http://www.chemicalbook.com/ChemicalProductProperty_EN_cb4111698.htm

External links

Sodium compounds

NaAlO₂ NaBH₄ NaBH₃(CN) NaBO₂ NaBiO₃ NaBr NaBrO NaBrO₃ NaCH₃COO NaC₆H₅CO₂ NaC₆H₄(OH)CO₂ NaCN NaCl NaClO NaClO₂ NaClO₃ NaClO₄ NaF Na₂FeO₄ NaH NaHCO₃ NaH₂PO₄ NaHSO₃ NaHSO₄ NaI NaIO₃ NaIO₄ Na₅IO₆ NaMnO₄ NaN₃ NaNH₂ NaNO₂ NaNO₃ NaOCN NaO₂ NaO₃ NaOH NaPO₂H₂ NaReO₄ NaSCN NaSH NaTcO₄ NaVO₃ Na₂CO₃ Na₂C₂O₄ Na₂CrO₄ Na₂Cr₂O₇ Na₂GeO₃ Na₂MnO₄ Na₃MnO₄ Na₂MoO₄ Na₂MoS₄ Na₂N₂O₂ Na₂O Na₂O₂ Na₂O(UO₃)₂ Na₂PO₃F Na₂S Na₂SO₃ Na₂SO₄ Na₂S₂O₃ Na₂S₂O₄ Na₂S₂O₅ Na₂S₂O₆ Na₂S₂O₇ Na₂S₂O₈ Na₂S₄O₆ Na₂Se Na₂SeO₃ Na₂SeO₄ Na₂SiO₃ Na₂Si₂O₅ Na₄SiO₄ Na₂Te Na₂TeO₃ Na₂TeO₄ Na₂Po Na₂Ti₃O₇ Na₂U₂O₇ NaWO₄ Na₂Zn(OH)₄ Na₃N Na₃P Na₃PO₄ Na₃VO₄ Na₄Fe(CN)₆ Na₄P₃O₇ Na₅P₃O₁₀

Chemical formulas

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