Sodium metabisulfite

Sodium metabisulfite
Names
Other names
Sodium pyrosulfite
Sodium disulfite
Identifiers
3D model (JSmol)
ChEBI
ECHA InfoCard 100.028.794
EC Number 231-673-0
E number E223 (preservatives)
RTECS number UX8225000
Properties
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
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
slightly soluble in ethanol
Hazards
Safety data sheet Mallinckrodt MSDS
Harmful (Xn)
Irritant (Xi)
R-phrases (outdated) R22 R31 R41
S-phrases (outdated) (S2) S26 S39 S46
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
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).
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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

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

See also

References

  1. 1 2 3 "NIOSH Pocket Guide to Chemical Hazards #0566". National Institute for Occupational Safety and Health (NIOSH).
  2. ↑ 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.
  3. ↑ 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
  4. ↑ "Food Additives approved by the EU" (PDF). Retrieved 12 March 2015.
  5. ↑ Dean D. Metcalfe, Ronald A. Simon, Food allergy: adverse reactions to food and food additives, Wiley-Blackwell 2003, p. 324–339
  6. ↑ http://www.ific.org/publications/brochures/asthmabroch.cfm
  7. ↑ 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.
  8. 1 2 "Food-Info.net : E-numbers : E223: Sodium disulphite". food-info.net.
  9. ↑ Anchell, Steve (2008). The darkroom cookbook (3rd ed.). Amsterdam: Focal Press. p. 193. ISBN 0240810554.
  10. ↑ http://www.bonideproducts.com/lbonide/msds/msds271.pdf
  11. ↑ Sodium sulfite. http://www.chemicalbook.com/ChemicalProductProperty_EN_cb4111698.htm
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