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E224 Potassium metabisulphite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent odour.
E224 Potassium metabisulphite is mainly used as an antioxidant or chemical sterilant.
As a disulfite, E224 Potassium metabisulphite is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably.
CAS: 16731-55-8
MF: K2O5S2
MW: 222.32
EINECS: 240-795-3
Synonyms
dipotassiumdisulfite;dipotassiummetabisulfite;Disulfurousacid,dipotassiumsalt;potassiummetabisulphate;pyrosulfurousacid,dipotassiumsalt;POTASSIUM METABISULFITE REAGENT;POTASSIUMMETABISULFITE,CRYSTAL,FCC;POTASSIUMMETABISULFITE,CRYSTAL,NF
E224 Potassium metabisulphite, also known as potassium metabisulfite, is an inorganic compound with the formula K2S2O5.
E224 Potassium metabisulphite appears as a white crystalline powder and is highly soluble in water, where it dissociates to release sulfite ions.
E224 Potassium metabisulphite is commonly used as a preservative and antioxidant in food and beverages, particularly in winemaking, due to its ability to inhibit microbial growth and oxidation.
In addition to its food applications, potassium pyrosulfite is utilized in various industrial processes, including photography and water treatment, where E224 Potassium metabisulphite acts as a reducing agent.
E224 Potassium metabisulphite has a relatively low toxicity, but exposure can cause irritation to the respiratory system and skin.
E224 Potassium metabisulphite is stable under normal conditions but should be stored in a cool, dry place away from strong acids and oxidizing agents to prevent decomposition.
Overall, E224 Potassium metabisulphite is valued for its versatility and effectiveness in both food preservation and industrial applications.
E224 Potassium metabisulphite has a monoclinic crystal structure.
E224 Potassium metabisulphite is an inorganic salt with antimicrobial properties.
E224 Potassium metabisulphite is a sulfiting agent that prevents browning of foods.
E224 Potassium metabisulphite is a synthetic chemical compound used primarily as a preservative and antioxidant.
E224 Potassium metabisulphite or potassium pyrosulfite, is a derivative of sulfur dioxide that can be used as a preservative, antioxidant, stabilizer and bleaching agent in food with the European food additive number E224.
E224 Potassium metabisulphite is commonly used in the production of wine, cider, juice, and beer brewing.
Generally, E224 Potassium metabisulphite can be made from the reaction between sulfur dioxide with potassium carbonate at temperatures between 50°C – 80°C and at a pH between 4 – 7.5.
The following are the brief three steps manufacturing processes:
Treat the solution of potassium hydroxide and/or potassium carbonate with sulfur dioxide gases to obtain potassium sulfite.
Here is the chemical reaction equation: K2CO3 + SO2 + H2O = K2SO3 + H2CO3
Still pass sulfur dioxide into the above aqueous solution until saturation is reached.
In this process, potassium sulfite is converted to potassium bisulfite.
Reaction equation: K2SO3 + SO2 + H2O = 2KHSO3
Finally, potassium metabisulfite (K2S2O5) is produced by cooling down the reaction mixture, and following filtration or centrifugation process.
Reaction equation: 2KHSO3 = K2S2O5+H2O
Chemical structure
Further information: Bisulfite
E224 Potassium metabisulphite is not a bisulfite (HSO−3), salts of which are rarely isolated.
Instead E224 Potassium metabisulphite is a pyrosulfite (S2O2−5), which would result from dehydration of the hypothetical bisulfite:
2 HSO−3 → O3S−SO2−2 + H2O
The sodium, potassium, and ammonium bisulfites behave similarly.
The S-S distance is about 222 pm and the S-O distances are near 147 pm.
A double salt with an authentic bisulfite anion has been characterized in the form of K5(HSO3)3(S2O5).
E224 Potassium metabisulphite Chemical Properties
Melting point: 190°C
density: 2.34 g/cm3
bulk density: 1000-1300kg/m3
vapor density: 2.3 (vs air)
storage temp.: Store at +5°C to +30°C.
solubility: H2O: 0.1 M at 20 °C, clear, colorless
form: Powder/Solid
color: White to slightly yellow
Specific Gravity: 2.3
Odor: Odorless
PH Range: 3-4.5 at 22.2 g/l at 25 °C
PH: 2.5-4.5 (25℃, 0.1M in H2O)
Water Solubility: Soluble in water. Insoluble in ethanol.
Sensitive: Air Sensitive
Decomposition: 150°C
λmax: 267nm(H2O)(lit.)
Merck: 14,7645
Cosmetics Ingredients Functions: REDUCING HAIR WAVING OR STRAIGHTENING PRESERVATIVE
InChI: S/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2
InChIKey: RWPGFSMJFRPDDP-UHFFFAOYSA-L
EPA Substance Registry System: E224 Potassium metabisulphite (16731-55-8)
Absorption: cut-off at 308nm in H2O at 0.1M
E224 Potassium metabisulphite occurs as white or colorless free-flowing crystals, crystalline powder, or granules, usually with an odor of sulfur dioxide.
Uses
E224 Potassium metabisulphite is a chemical preservative and antioxi- dant obtained as white or colorless crystals, powder, or granules.
E224 Potassium metabisulphite is soluble in water and insoluble in alcohol.
The sulfite salt yields sulfurous acid at a low ph. it is used as a food preservative.
E224 Potassium metabisulphite is used as a chemical preservative.
As antifermentative in breweries and wineries; bleaching straw; preservative for fruits and vegetables.
E224 Potassium metabisulphite is used as a food additive, also known as E224.
E224 Potassium metabisulphite is restricted in use and may cause allergic reactions in some sensitive persons.
Wine
E224 Potassium metabisulphite is a common wine or must additive, in which it forms sulfur dioxide (SO2).
E224 Potassium metabisulphite is a disinfectant.
E224 Potassium metabisulphite also acts as a potent antioxidant, protecting both the color and delicate flavors of wine.
A high dose would be 3 grams of E224 Potassium metabisulphite per six-gallon bucket of must or around 132 milligrams per liter (yielding roughly 75 ppm of SO2) prior to fermentation; then 6 grams per six-gallon bucket (150 ppm of SO2) at bottling.
Some countries regulate the SO2 content of wines.
Winemaking equipment is sanitized by spraying with a 1% SO2 (2 tsp E224 Potassium metabisulphite per L) solution.
Beer
E224 Potassium metabisulphite is sometimes used in the brewing industry to inhibit the growth of wild bacteria and fungi.
This step is called 'stabilizing'.
E224 Potassium metabisulphite is also used to neutralize monochloramine from tap water.
E224 Potassium metabisulphite is used both by homebrewers and commercial brewers alike.
E224 Potassium metabisulphite is not used as much for brewing beer, because the wort is almost always boiled, which kills most microorganisms.
Other uses
E224 Potassium metabisulphite is sometimes added to lemon juice as a preservative.
E224 Potassium metabisulphite is used in the textile industry for dyeing and cotton printing.
E224 Potassium metabisulphite is sometimes used to precipitate gold from solution in aqua regia (as an alternative to sodium sulfite).
E224 Potassium metabisulphite is a component of certain photographic developers and solutions used in photographic processing, keeping active developing species from contact with oxygen.
E224 Potassium metabisulphite is used as a bleaching agent in the production of coconut cream.
E224 Potassium metabisulphite is used in some pickles as a preservative.
E224 Potassium metabisulphite is used in tint etching iron-based metal samples for microstructural analysis.
E224 Potassium metabisulphite is used in aam papad as a preservative.
Pharmaceutical Applications
E224 Potassium metabisulphite is used in applications similar to those of sodium metabisulfite in pharmaceuticals, and in the food, brewing, and wine making industries.
E224 Potassium metabisulphite is used as an antioxidant, antimicrobial preservative and sterilizing agent.
Benefits
-Approved for use in food and beverage products
-Prevents microorganisms from growing and reproducing
-Prevents biological spoilage
-Has antioxidant properties
-Increases the stability and prolongs shelf life of wine, cider and beer
-Can be used for the removal of free chlorine in tap water which can cause chlorophenolic off flavours in beer
-Can be used as an alternative to Sodium Metabisulphate where sodium salt is not preferred.
Contact allergens
E224 Potassium metabisulphite is an antioxidant used as an antifermentative agent in breweries and wineries, as a preservative of fruits and vegetables, and to bleach straw.
Reactions to both sodium and E224 Potassium metabisulphite are expected.
Preparation and reactions
E224 Potassium metabisulphite can be prepared by treating a solution of potassium hydroxide with sulfur dioxide.
2 SO2 + 2 KOH → K2S2O5 + H2O
E224 Potassium metabisulphite decomposes at 190 °C, yielding potassium sulfite and sulfur dioxide:
K2S2O5 → K2SO3 + SO2
