POTASSIUM METABISULPHITE

Potassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent odour. 
Potassium metabisulfite is mainly used as an antioxidant or chemical sterilant.
Potassium metabisulfite is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. 

CAS Number: 4429-42-9
Molecular Formula: K2O5S2
Molecular Weight: 222.32
EINECS Number: 240-795-3

Synonyms:Potassium metabisulfite, 16731-55-8, Potassium disulfite, Dipotassium pyrosulfite, Dipotassium disulfite, Sobisu, Dipotassium metabisulfite, Potassium metabisulphite, Potassium disulfite K2S2O5, Potassium pentaoxodisulfate, Pyrosulfurous acid dipotassium salt, INS-224, Potassium metabisulfite E224, 65OE787Q7W, DTXSID1021293, E-224, RefChem:867887, DTXCID401293, 240-795-3, Potassium pyrosulfite, Potassium metabisulfite NF, MFCD00167605, Dipotassium disulphite, CCRIS 1427, HSDB 5062, EINECS 240-795-3, Kaliumpyrosulfit, UNII-65OE787Q7W, EC 240-795-3, SCHEMBL29531, CHEMBL2106901, Potassium metabisulfite II, Potassium metabisulfite MI, Potassium metabisulfite FCC, Potassium metabisulfite HSDB, AKOS015912829, Potassium metabisulfite MART, Potassium metabisulfite VANDF, Potassium metabisulfite WHO-DD, DB-231696, NS00013994, P2480, Potassium metabisulfite EP impurity, Potassium metabisulfite EP monograph, D05581, F095812, Q417881, POTASSIUM BISULPHITE;POTASSIUM BISULFITE;POTASSIUM DISULFITE;POTASSIUM M-BISULFITE;POTASSIUM METABISULPHITE;POTASSIUM PYROSULFITE;DI-POTASSIUM DISULPHITE;DIPOTASSIUM PYROSULFITE

Potassium metabisulfite has a monoclinic crystal structure.
Potassium metabisulphite (also known as potassium pyrosulfite) is an inorganic salt, widely used as a preservative, antioxidant, and reducing agent in food, beverage, and industrial applications.
Its chemical formula is K₂S₂O₅.

Potassium metabisulfite belongs to the class of sulfite/metabisulfite salts.
Chemically, it consists of two potassium ions (K⁺) and a metabisulfite ion (S₂O₅²⁻).
In aqueous solution, it hydrolyzes to form bisulfite (HSO₃⁻) species.

This gives it strong reducing and antioxidant properties.
Physically, potassium metabisulphite appears as a white crystalline powder or granular solid.
It is soluble in water and releases sulfur dioxide odor.

Potassium metabisulfite is stable in dry form but decomposes in moisture.
Potassium metabisulfite exhibits strong reducing properties, reacting readily with oxidizing agents.
Potassium metabisulfite helps prevent oxidation reactions.

Potassium metabisulfite releases sulfur dioxide (SO₂) when dissolved or acidified.
SO₂ provides antimicrobial and antioxidant effects.
This is key to its functionality.

Potassium metabisulfite is chemically stable under dry conditions, but sensitive to air, moisture, and heat.
It can oxidize to form sulfates over time.
Proper storage is necessary.

Potassium metabisulfite is widely used in food preservation, water treatment, and chemical processing.
Potassium metabisulfite helps control oxidation and microbial growth.
This highlights its importance.

Potassium metabisulfite is best described as a reactive inorganic sulfite salt that releases sulfur dioxide for antioxidant and antimicrobial action, widely used in food, beverages, and industrial systems.
Potassium metabisulfite exhibits strong nucleophilic character, allowing it to react readily with electrophilic compounds such as carbonyl groups.
It forms stable bisulfite addition products.

Potassium metabisulfite functions as an effective oxygen scavenger, reacting with dissolved oxygen in aqueous systems.
Potassium metabisulfite helps prevent oxidative degradation.
This is important in water and beverage systems.

Potassium metabisulfite shows bleaching and decolorizing properties, particularly in textile and food processing.
Potassium metabisulfite can reduce colored compounds to colorless forms.
This improves product appearance.

Potassium metabisulphite can influence microbial metabolism by releasing SO₂, which inhibits enzyme systems in microorganisms.
This suppresses growth of yeasts, molds, and some bacteria.
This supports preservation.

Melting point: 190 °C
solubility: H2O: 0.1 M at 20 °C, clear, colorless
Cosmetics Ingredients Functions: HAIR WAVING OR STRAIGHTENING
REDUCING: PRESERVATIVE

Potassium metabisulphite can be prepared by treating a solution of potassium hydroxide with sulfur dioxide: 2 SO2 + 2 KOH → K2S2O5 + H2O
It decomposes at 190 °C, yielding potassium sulfite and sulfur dioxide: K2S2O5 → K2SO3 + SO2
Potassium metabisulphite (K₂S₂O₅) is formed by reacting sulfur dioxide (SO₂) with potassium carbonate or potassium hydroxide, followed by crystallization.

This produces a stable solid salt.
Potassium metabisulphite is widely manufactured industrially.
In aqueous solution, it establishes an equilibrium between metabisulfite (S₂O₅²⁻), bisulfite (HSO₃⁻), and dissolved SO₂.

The dominant species depends on pH.
This governs its reactivity.
Potassium metabisulphite exhibits moderate acidity upon dissolution, due to formation of bisulfite ions.

Potassium metabisulphite can act as both an acid and a reducing agent.
This dual behavior is important in applications.
Potassium metabisulphite shows strong antioxidant activity, reacting with oxygen and reactive oxidizing species.

Potassium metabisulphite interrupts oxidation chains.
This protects sensitive compounds.
Potassium metabisulphite demonstrates antimicrobial properties via SO₂ release.

Sulfur dioxide inhibits enzymes in microorganisms.
Potassium metabisulphite can form bisulfite addition compounds with aldehydes and ketones.
These adducts are useful in purification and stabilization.

This is a classical chemical application.
The compound is highly soluble in water, forming active sulfite species.
It is easy to dose and apply in liquid systems.

It is sensitive to air, moisture, and heat, which can lead to oxidation into potassium sulfate.
This reduces its effectiveness over time.
Potassium metabisulphite is a dynamic sulfite system with antioxidant, antimicrobial, and nucleophilic properties, widely used in preservation, purification, and industrial processing.

It demonstrates buffer-like behavior in certain pH ranges, helping stabilize chemical environments.
This is useful in controlled processes.
It enhances consistency.

Potassium metabisulphite may interact with metal ions, sometimes forming complexes or affecting corrosion processes.
This can influence industrial system behavior.
It is relevant in processing applications.

Potassium metabisulphite is often used in controlled dosing systems to regulate SO₂ release and avoid excessive exposure.
This ensures safe and effective use.
It improves process control.

Because of its reactivity, it is important to handle and store it in dry, sealed conditions to maintain activity.
Exposure to moisture reduces effectiveness.
Potassium metabisulphite is a highly reactive, multifunctional sulfite compound with antioxidant, antimicrobial, and nucleophilic properties, making it essential in preservation, processing, and chemical applications.

Uses Of Potassium metabisulphite:
It is used as a food additive, also known as E224.
Potassium metabisulphite is restricted in use and may cause allergic reactions in some sensitive persons.
Potassium metabisulfite is a common wine or must additive, in which it forms sulfur dioxide (SO2). Sulfur dioxide is a disinfectant. It also acts as a potent antioxidant, protecting both the color and delicate flavors of wine.

Potassium metabisulphite is sometimes used in the brewing industry to inhibit the growth of wild bacteria and fungi. 
Potassium metabisulphite is also used to neutralize monochloramine from tap water. 
Potassium metabisulphite is used both by homebrewers and commercial brewers alike.
 
Potassium metabisulphite is not used as much for brewing beer, because the wort is almost always boiled, which kills most microorganisms.
Potassium metabisulfite is sometimes added to lemon juice as a preservative.
Potassium metabisulfite is used in the textile industry for dyeing and cotton printing.

Potassium metabisulfite is sometimes used to precipitate gold from solution in aqua regia (as an alternative to sodium sulfite).
It is a component of certain photographic developers and solutions used in photographic processing, keeping active developing species from contact with oxygen.
Potassium metabisulphite is used as a bleaching agent in the production of coconut cream.

Potassium metabisulphite is used in some pickles as a preservative.
It is used in tint etching iron-based metal samples for microstructural analysis.[7]
Potassium metabisulphite is used in aam papad as a preservative.

Potassium metabisulphite is widely used in the food and beverage industry as a preservative and antioxidant (E224).
It prevents oxidation and microbial spoilage.
This extends shelf life.

In wine production, it is one of the most important additives.
It controls oxidation and inhibits unwanted yeasts and bacteria.
This stabilizes flavor and quality.

It is applied in beer and cider production to protect against oxidation and contamination.
It helps maintain product stability.
This improves shelf life.

In fruit processing, such as dried fruits and juices, it prevents enzymatic browning.
It preserves color and freshness.
This enhances product appearance.

Potassium metabisulphite is used in water treatment systems as an oxygen scavenger and dechlorinating agent.
It removes dissolved oxygen and chlorine.
This protects equipment and improves water quality.

In textile and paper industries, it is used as a bleaching and decolorizing agent.
It helps remove unwanted color.
This improves material quality.

Potassium metabisulphite is applied in chemical synthesis as a reducing agent and intermediate.
It participates in sulfur-based reactions.
This supports industrial processes.

In leather processing, it helps preserve hides and control microbial growth.
Potassium metabisulphite improves processing efficiency.
This enhances product quality.

Potassium metabisulphite is also used in analytical chemistry for forming bisulfite addition compounds with aldehydes.
It aids purification and identification.
Potassium metabisulphite is used wherever antioxidant protection, microbial control, oxygen removal, and reduction reactions are required, especially in food, beverages, water treatment, and industrial processes.

Safety Profile Of Potassium metabisulphite:
Potassium metabisulphite presents moderate hazards, mainly due to its ability to release sulfur dioxide (SO₂), irritation potential, and reducing properties.
It requires careful handling, especially in moist conditions.
Proper safety precautions are necessary.

Skin contact may cause irritation, particularly with prolonged exposure to powder or solution.
Symptoms can include redness or dryness.
Protective gloves are recommended.

Eye contact can cause moderate to severe irritation.
Symptoms include redness, pain, and watering.
Immediate rinsing with plenty of water is necessary.

Inhalation of dust or released SO₂ gas is a significant hazard.
It can cause respiratory irritation, coughing, and breathing difficulty.
Sensitive individuals (e.g., asthmatics) may experience stronger effects.

Ingestion is harmful and may cause gastrointestinal irritation and systemic effects.
Symptoms may include nausea, vomiting, and abdominal discomfort.

Medical attention should be sought if swallowed.
Potassium metabisulphite is not flammable, but it decomposes when heated or in contact with acids.