Potassium metabisulfite

• BPPotassium Metabisulphite
• Ph. Eur.Potassium Metabisulfite
• USP–NFPotassium Metabisulfite

Dipotassium disulfite; dipotassium pentaoxodisulfate; kalii metabisulfis; potassium disulfite; potassium pyrosulfite; E224

Dipotassium disulfite · [16731-55-8]

UNII 65OE787Q7W · PubChem CID 28019

K2S2O5 · 222.32

Antioxidant, chelating agent

Typical concentrations: — · Dosage forms: Liquid

Used, like sodium metabisulfite, as an antioxidant in oral, parenteral and topical preparations, mainly in acidic formulations, and as an antimicrobial preservative in acidic foods and beverages; it is widely used in wine-making. Concentrations comparable to those of sodium metabisulfite (generally about 0.01–1.0% w/v) are used. It is chosen in preference to the sodium salt when sodium intake is to be limited.

Colourless, free-flowing crystals, or a white crystalline powder or granules, with an odour of sulfur dioxide.

Sulfur dioxide content

theoretical about 57.6% SO2

Solubility

freely soluble in water; very slightly soluble in ethanol

Solution pH

aqueous solutions are acidic

Thermal behaviour

decomposes on heating at about 190 °C, releasing sulfur dioxide

On exposure to air and moisture it is slowly oxidised to potassium sulfate, with loss of sulfur dioxide and of antioxidant capacity. Store in a well-filled, airtight container, protected from light, in a cool, dry place.

Reacts with acids to release sulfur dioxide and is incompatible with oxidising agents. Sulfites react with sympathomimetics that have ortho- or para-hydroxybenzyl alcohol groups (such as adrenaline), forming inactive sulfonic acid derivatives, inactivate cisplatin, destroy thiamine and can react with chloramphenicol and phenylmercuric acetate.

Prepared by passing sulfur dioxide into a solution of potassium hydroxide or potassium carbonate until it is saturated, and crystallising the product.

Sulfites can cause hypersensitivity reactions, including bronchospasm and anaphylactoid reactions, particularly in people with asthma. In the body sulfite is oxidised to sulfate by sulfite oxidase. EFSA and JECFA have set a group ADI for sulfur dioxide and sulfites expressed as SO2.

Handle in a well-ventilated area, as sulfur dioxide may be released, especially in contact with acids or moisture. Eye protection and gloves are recommended.

GRAS listed as a chemical preservative, although sulfites may not be used in meats, in foods that are recognised sources of thiamine or on fresh fruit and vegetables intended to be eaten raw. Accepted as a food additive in Europe (E224). Labelling of sulfites is required for foods in the USA and EU.

Sodium bisulfite; sodium metabisulfite; sodium sulfite.

In solution metabisulfite forms bisulfite; at low pH sulfurous acid and free sulfur dioxide predominate, while sulfite predominates at higher pH, so the choice among sulfite antioxidants depends on the pH of the formulation.