Sodium metabisulfite

Sodium metabisulfite
Other names

Sodium pyrosulfite
Sodium disulfite
Identifiers
CAS number 7681-57-4 Y
PubChem 24346
EC number 231-673-0
RTECS number UX8225000
Properties
Molecular formula Na2S2O5, Na-O-(S=O)-O-(S=O)-O-Na
Molar mass 190.107 g/mol
Appearance white powder
Density 1.48 g/cm3
Melting point

>170 °C (begins at 150 °C)
Solubility in water 54 g/100 ml
Hazards
MSDS Mallinckrodt MSDS
EU Index 016-063-00-2
EU classification Harmful (Xn)
Irritant (Xi)
R-phrases R22 R31 R41
S-phrases (S2) S26 S39 S46
NFPA 704
0
2
0
Related compounds
Other anions Sodium sulfite
Sodium bisulfite
Other cations Potassium metabisulfite
Related compounds Sodium dithionite
Sodium thiosulfate
Sodium sulfate
 Y (verify) (what is: Y/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

Contents

Chemical structure

The anion is a hybride 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.[1]

Uses

Food additive

It is used as a preservative and antioxidant in food and is also known as E223.[2]

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.[3][4]

Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.[5]

The acceptable daily intake is up to 0.7 mg per kg of body weight.[6] Sodium metabisulfite has no side effects; it is oxidised in the liver to harmless sulfate and excreted in urine.[7]

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 it releases sulfur dioxide, leaving sodium oxide behind:

Na2S2O5 → Na2O + 2 SO2

See also

External links

References

  1. ^ K. L. Carter, T. A. Siddiquee, K. L. Murphy, D. W. Bennett "The surprisingly elusive crystal structure of sodium metabisulfite" Acta Cryst. (2004). B60, 155-162. doi:10.1107/S0108768104003325
  2. ^ http://www.eufic.org/upl/1/en/doc/EUFIC%20e-number%20mini%20guide%202.pdf
  3. ^ Dean D. Metcalfe, Ronald A. Simon, Food allergy: adverse reactions to food and food additives, Wiley-Blackwell 2003, pp 324-339
  4. ^ http://www.ific.org/publications/brochures/asthmabroch.cfm
  5. ^ Milne, George W. A. (2005). Gardner's commercially important chemicals: synonyms, trade names, and properties. New York: Wiley-Interscience. pp. 568. ISBN 0-471-73518-3. 
  6. ^ http://www.food-info.net/uk/e/e223.htm
  7. ^ Food-Info.net : E-numbers : E223: Sodium disulphite
  8. ^ http://silvergrain.com/labs/Metabisulfite
  9. ^ http://www.bonideproducts.com/lbonide/msds/msds271.pdf