Sodium metabisulfite

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Sodium metabisulfite
Sodium metabisulfite
Structure of sodium metabisulfite
Identifiers
CAS number7681-57-4 YesY
PubChem656671
EC number231-673-0
ChEMBLCHEMBL2016976 N
RTECS numberUX8225000
Jmol-3D imagesImage 1
Properties
Molecular formulaNa2S2O5, Na-O-(S=O)-O-(S=O)-O-Na
Molar mass190.107 g/mol
Appearancewhite to yellow powder
Odorfaint SO2
Density1.48 g/cm3
Melting point170 °C (338 °F; 443 K) decomp begins at 150°C
Solubility in water45.1 g/100 mL (0 °C)
65.3 g/100 mL (20 °C)
81.7 g/100 mL (100 °C)
Solubilityvery soluble in glycerol
soluble in ethanol
Hazards
MSDSMallinckrodt MSDS
EU Index016-063-00-2
EU classificationHarmful (Xn)
Irritant (Xi)
R-phrasesR22 R31 R41
S-phrases(S2) S26 S39 S46
NFPA 704
Related compounds
Other anionsSodium sulfite
Sodium bisulfite
Other cationsPotassium metabisulfite
Related compoundsSodium dithionite
Sodium thiosulfate
Sodium sulfate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references
 
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Sodium metabisulfite
Sodium metabisulfite
Structure of sodium metabisulfite
Identifiers
CAS number7681-57-4 YesY
PubChem656671
EC number231-673-0
ChEMBLCHEMBL2016976 N
RTECS numberUX8225000
Jmol-3D imagesImage 1
Properties
Molecular formulaNa2S2O5, Na-O-(S=O)-O-(S=O)-O-Na
Molar mass190.107 g/mol
Appearancewhite to yellow powder
Odorfaint SO2
Density1.48 g/cm3
Melting point170 °C (338 °F; 443 K) decomp begins at 150°C
Solubility in water45.1 g/100 mL (0 °C)
65.3 g/100 mL (20 °C)
81.7 g/100 mL (100 °C)
Solubilityvery soluble in glycerol
soluble in ethanol
Hazards
MSDSMallinckrodt MSDS
EU Index016-063-00-2
EU classificationHarmful (Xn)
Irritant (Xi)
R-phrasesR22 R31 R41
S-phrases(S2) S26 S39 S46
NFPA 704
Related compounds
Other anionsSodium sulfite
Sodium bisulfite
Other cationsPotassium metabisulfite
Related compoundsSodium dithionite
Sodium thiosulfate
Sodium sulfate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
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[edit]

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.[1]

Chemical structure[edit]

The anion 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.[2]

Uses[edit]

Food additive[edit]

It is used as a preservative and antioxidant in food and is also known as E223.[3]

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.[4][5]

Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.[6]

The acceptable daily intake is up to 0.7 mg per kg of body weight.[7] Sodium metabisulfite has no side effects; it is oxidised in the liver to harmless sulfate and excreted in urine.[8] [clarification needed]

Sanitization and cleaning agent[edit]

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[edit]

Chemical properties[edit]

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[edit]

References[edit]

  1. ^ 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. 
  2. ^ 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
  3. ^ http://www.eufic.org/upl/1/en/doc/EUFIC%20e-number%20mini%20guide%202.pdf
  4. ^ Dean D. Metcalfe, Ronald A. Simon, Food allergy: adverse reactions to food and food additives, Wiley-Blackwell 2003, pp 324-339
  5. ^ http://www.ific.org/publications/brochures/asthmabroch.cfm
  6. ^ 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. 
  7. ^ http://www.food-info.net/uk/e/e223.htm
  8. ^ Food-Info.net : E-numbers : E223: Sodium disulphite
  9. ^ http://silvergrain.com/labs/Metabisulfite
  10. ^ http://www.bonideproducts.com/lbonide/msds/msds271.pdf
  11. ^ Sodium sulfite. http://www.chemicalbook.com/ChemicalProductProperty_EN_cb4111698.htm

External links[edit]