Metabisulfite
Encyclopedia
A disulfite, commonly known as metabisulfite, is a chemical compound
containing the disulfite ion (metabisulfite ion) [S2O52−].
ion (HSO3−). It can arise from:
dehydration
In aqueous solution, the disulfite ion is formed in minor amounts by dehydration of bisulfite in an equilibrium:
Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.
In fact, disulfite is the ion of disulfurous acid
(pyrosulfurous acid), which originates from sulfurous acid
in accordance with the dehydration reaction above:
addition
The disulfite ion also arises from the addition of sulfur dioxide
to the sulfite
ion:
S2O52− + H+ → HSO3− + SO2
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
containing the disulfite ion (metabisulfite ion) [S2O52−].
Production of the disulfite ion
The disulfite ion is a dimer of the bisulfiteBisulfite
Bisulfite ion is the ion HSO3−. Salts containing the HSO3− ion are termed bisulfites also known as sulfite lyes...
ion (HSO3−). It can arise from:
dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
In aqueous solution, the disulfite ion is formed in minor amounts by dehydration of bisulfite in an equilibrium:
- 2 HSO3− (aq) S2O52− (aq) + H2O (l)
Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.
In fact, disulfite is the ion of disulfurous acid
Disulfurous acid
Disulfurous acid or pyrosulfurous acid is an oxoacid of sulfur with the formula H2S2O5. The salts of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid , a phantom acid, which does not exist in the free state.In contrast to disulfate , disulfite has...
(pyrosulfurous acid), which originates from sulfurous acid
Sulfurous acid
Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
in accordance with the dehydration reaction above:
- 2 H2SO3 → 2 HSO3− + 2 H+ → H2S2O5 + H2O
addition
The disulfite ion also arises from the addition of sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
to the sulfite
Sulfite
Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...
ion:
| HSO3− SO32− + H+ SO32− + SO2 S2O52− |
Other reactions
In aqueous solution, disulfite salts decompose with acids:S2O52− + H+ → HSO3− + SO2
Examples of disulfites
- sodium metabisulfiteSodium metabisulfiteSodium metabisulfite or sodium pyrosulfite is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium...
(E223E numberE numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
) and potassium metabisulfitePotassium metabisulfitePotassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent sulfur odour. The main use for the chemical is as an antioxidant or chemical sterilant. It is a disulfite and is chemically very similar to sodium metabisulfite, with which it is...
(E224) are used as a preservativePreservativeA preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
and antioxidantAntioxidantAn antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
in food.