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Sodium metabisulphite is highly soluble in water, where it forms bisulfite ions and releases sulfur dioxide (SO₂), especially under acidic conditions.
Sodium metabisulphite is effective in preventing oxidation, discoloration, and microbial growth in various formulations.
Sodium metabisulphite is widely used in food, pharmaceutical, water treatment, and industrial applications due to its strong reducing and antimicrobial properties.
CAS Number: 7681-57-4
EC Number: 231-673-0
Molecular Formula: Na2S2O5
Molecular Weight: 190.10 g/mol
Synonyms: Sodium Metabisulfite, Disodium Metabisulfite, Sodium Pyrosulfite, Sodium Disulfite, Sodium Bisulfite Anhydride, E223, Metabisulphite of Soda, Sodium Pyrosulphite, Sodium Disulphite, Sulfurous Acid Sodium Salt (dimer), Disodium Pyrosulfite, Sodium Sulfite Dimer, Antioxidant E223, Food Grade Metabisulfite, SMBS, Sodium Metabisulphite Powder
Sodium metabisulphite is an inorganic sulfur-based compound commonly used as an antioxidant, preservative, and reducing agent.
Sodium metabisulphite appears as a white to slightly yellow crystalline powder with a characteristic sulfur dioxide odor.
Sodium metabisulphite is highly soluble in water, where it forms bisulfite ions and releases sulfur dioxide (SO₂), especially under acidic conditions.
Sodium metabisulphite is widely used in food, pharmaceutical, water treatment, and industrial applications due to its strong reducing and antimicrobial properties.
Sodium metabisulphite is effective in preventing oxidation, discoloration, and microbial growth in various formulations.
Sodium metabisulphite plays an important role in food preservation (e.g., dried fruits, juices), winemaking, and brewing by inhibiting microbial activity and enzymatic browning.
Sodium metabisulphite is also used in water treatment for dechlorination, in textile and paper industries as a bleaching agent, and in chemical processes as a reducing agent.
Sodium metabisulphite is an inorganic compound of chemical formula Na2S2O5.
Sodium metabisulphite is sometimes referred to as diSodium metabisulphite.
Sodium metabisulphite is used as a disinfectant, antioxidant, and preservative agent.
When dissolved in water Sodium metabisulphite forms sodium bisulfite.
Sodium metabisulphite is used as a preservative and antioxidant in food.
Sodium metabisulphite is used as a cleaning agent for potable water desalination systems and used to remove chloramine from drinking water after treatment.
Sodium Metabisulphite is a sodium salt of disulphuric acid.
Sodium metabisulphite is unstable, reacts easily with water and oxygen, and forms more stable sulphur compounds in the process.
As it hydrolyses and oxidises quickly, Sodium Metabisulphite does not occur in nature in its pure form and is produced exclusively synthetically.
Applications of Sodium Metabisulphite:
Sodium metabisulphite is used in the following products: pH regulators and water treatment products, water treatment chemicals, fertilizers, washing and cleaning products, fillers, putties, plasters, modeling clay, leather processing products, paper chemicals and paints, photochemicals, varnishes and waxes, and textile processing products and dyes.
Sodium metabisulphite is used in the manufacture of wood and wood products, furniture and pulp, paper and paper products, mining.
The release of Sodium metabisulphite into the environment may occur from industrial use: in processing aids at industrial sites, as a processing aid, formulation of mixtures, manufacture of the substance, formulation in materials, as an intermediate step in the further manufacture of another substance (use intermediates) and in the manufacture of articles.
Sodium metabisulphite is used in machine wash liquids/detergents, automotive care products, paints and coatings or adhesives, fragrances and air fresheners.
Uses of Sodium Metabisulphite:
Sodium metabisulphite have many major and niche uses.
Sodium metabisulphite is widely used for preserving food and beverages.
Sodium metabisulphite is one of the main ingredients in "Drywhite", a composition used to prevent chipped potatoes oxidising during storage prior to use in many fish and chip shops.
Sodium metabisulphite is added as an excipient to medications which contain adrenaline (epinephrine), in order to prevent the oxidation of adrenaline.
For example, Sodium metabisulphite is added to combination drug formulations which contain a local anaesthetic and adrenaline and to the formulation in epinephrine autoinjectors, such as the EpiPen.
This lengthens the shelf life of the formulation, although the Sodium metabisulphite reacts with adrenaline, causing it to degrade and form epinephrine sulfonate.
In combination with sodium hydrosulfite it is used as a rust-stain remover.
Sodium metabisulphite is used in photography as an antioxidant in photographic film development.
Concentrated Sodium metabisulphite can be used to remove tree stumps. Some brands contain 98% Sodium metabisulphite, and cause degradation of lignin in the stumps, facilitating removal.
Sodium metabisulphite is also used as an excipient in some tablets, such as paracetamol.
Sodium metabisulphite can be added to a blood smear in a test for sickle cell anaemia (and other similar forms of haemoglobin mutation).
Sodium metabisulphite causes defunct cells to sickle (through a complex polymerisation) hence confirming disease.
Sodium metabisulphite is used as a bleaching agent in the production of coconut cream.
Sodium metabisulphite is commonly used as an antimicrobial and antioxidant in winemaking; bottled wine indicates its use with the label "Contains Sulfites" in the US.
Sodium metabisulphite is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibres, thus allowing the garment to go back to its original shape after washing.
Sodium metabisulphite is used as an SO2 source (mixed with air or oxygen) for the destruction of cyanide in commercial gold cyanidation processes.
Sodium metabisulphite is used as an SO2 source (mixed with air or oxygen) for the precipitation of elemental gold in chloroauric (aqua regia) solutions.
Sodium metabisulphite is used in the water treatment industry to quench residual chlorine.
Sodium metabisulphite is used in tint etching iron-based metal samples for microstructural analysis.
Sodium metabisulphite is used as a fungicide for anti-microbe and mould prevention during shipping of consumer goods such as shoes and clothing.
Plastic stickers and packaging (such as Micro-Pak™) containing the anhydrous, Sodium metabisulphite solid active ingredient are added prior to shipping.
The devices absorb moisture from the atmosphere during shipping and release low levels of sulfur dioxide.
Sodium metabisulphite is used for preserving fruit during shipping.
Sodium metabisulphite is used as an additive in the extraction of starch from tubers, fruit and cereal crops.
Sodium metabisulphite is used as a pickling agent to treat high pressure reverse osmosis and nanofiltration water desalination membranes for extended storage periods between uses.
Sodium metabisulphite is used to create a bisulfite adduct from ketones to aid in separation of the ketone product.
The usage of metabisulfite versus the sulfite is also more entropically favourable.
Sodium Metabisulphite in the food industry:
Under the designation E 223, Sodium Metabisulphite is used in the food industry as a preservative and antioxidant.
Sodium metabisulphite extends shelf life, prevents discolouration and inhibits the growth of microorganisms.
Typical applications include:
Dried fruit:
Sodium metabisulphite prevents browning and ensures colour stability
Potato products:
Sodium metabisulphite prevents enzymatic darkening
Meat products:
Sodium metabisulphite prevents oxidative discolouration and microbial spoilage
Seafood:
Sodium metabisulphite preserves colour and delays spoilage
Baked goods:
Sodium metabisulphite stabilises fats and improves storage stability
Fruit juices:
Sodium metabisulphite stabilises colour and preserves aroma
Beer:
Sodium metabisulphite reduces oxidative processes to ensure flavour stability
Wine (sulphurisation):
Sodium metabisulphite stabilises the fermentation process and protects against oxidation
Sodium Metabisulphite in the cleaning industry:
Sodium Metabisulphite is widely used in cleaning products due to its reducing, disinfecting and bleaching properties, for example in the following areas:
Neutralisation of chlorine and peroxide residues in food and beverage facilities
Reduction of oxidative damage to sensitive materials
Textile cleaning:
Removal of discolouration and increase in whiteness
Component of detergents and bleaching agents for chemical cleaning and brightening
Reduction of iron and copper salts that cause stains
Protection of textiles from oxidation damage during aggressive washing and cleaning processes.
Sodium Metabisulphite in water treatment:
In water treatment applications, Sodium Metabisulphite is used to neutralise oxidising agents (chlorine, ozone).
Sodium metabisulphite protects:
Pipes
Filters
Components in desalination plants
Cooling circuits in industry and power stations
Sodium Metabisulphite also prevents corrosion and deposits caused by oxidising agents.
Sodium Metabisulphite in the textile and leather goods industry:
Sodium Metabisulphite is used by textile manufacturers as a reducing bleaching agent and removes unwanted dyes or discolouration.
Other areas of application include:
Increasing the whiteness of cotton, linen and synthetic fibres
Reducing oxidative dyes for even colouring
Neutralising iron salts that cause stains
Stabilising flour for textile processing (anti-caking)
Areas of application in the leather industry include:
Removal of oxidised stains and discolouration
Reduction of toxic chromium(VI) compounds to chromium(III) in chrome tanning
Prevention of shrinkage stains by reducing oxidative residues
Futher areas of application for Sodium Metabisulphite:
Sodium Metabisulphite in the pharmaceutical industry:
Sodium Metabisulphite is used in the pharmaceutical industry due to its strong antioxidant properties.
The main applications are:
Protection of sensitive active ingredients from oxidation (e.g. in injection solutions, infusions, eye drops)
Preservation of liquid forms of medication
Reduction of metal ions (Fe3+, Cu2+) that could catalyse reactions
Reduced reagent in synthesis pathways of pharmaceutical active ingredients
Cleaning of equipment by neutralising chlorine or ozone residues
Sodium Metabisulphite in the cosmetics industry:
Sodium Metabisulphite has antioxidant, preservative and reducing properties in cosmetic products.
Typical applications are:
Stabilisation of sensitive ingredients (e.g. vitamin C)
Prevention of discolouration in creams and lotions
Stabilisation of dyes in hair colourants
Component of perm and hair straightening products, influencing sulphur bridges in the hair
Use in skin lightening products due to its reducing effect
Stabilisation of anti-ageing formulations
Improvement of the consistency and stability of make-up emulsions
Stabilisation of dyes and solvents in nail care products.
Sodium Metabisulphite in the construction industry:
Sodium Metabisulphite is used in a variety of ways in the construction industry due to its reducing properties.
Some examples:
Neutralisation of chlorine in construction projects, especially in water treatment
Reduction of heavy metals in wastewater from cement and building material production
Removal of iron-containing discolouration in concrete and mortar
Removal of rust and oxidation stains on concrete, natural stone and clinker
Intermediate product for construction chemicals
Component of additives to improve the storage stability of construction products
Other areas of application for Sodium Metabisulphite:
In the paper industry, Sodium Metabisulphite is used as a bleaching agent for paper and pulp, and in photography for the reduction of silver halides in film development.
Properties of Sodium Metabisulphite:
Sodium Metabisulphite is a whitish to yellowish crystalline powder with a pungent odour and a strong hygroscopic effect.
In water, Sodium metabisulphite decomposes into sodium hydrogen sulphite, which can react further to form sulphites or sulphur dioxide (SO2) depending on the pH value.
Sodium Metabisulphite acts as a strong reducing agent.
Sodium metabisulphite oxidises to sodium sulphate in air and also decomposes when heated to form sodium sulphate and sulphur dioxide.
Preparation of Sodium Metabisulphite:
Sodium metabisulphite can be prepared by treating a solution of sodium hydroxide with sulfur dioxide.
When conducted in warm water, Na2SO3 initially precipitates as a yellow solid.
With more SO2, the solid dissolves to give the disulfite, which crystallises upon cooling.
SO2 + 2 NaOH → Na2SO3 + H2O
SO2 + Na2SO3 → Na2S2O5
which yields a residue of colourless solid Na2S2O5.
Production of Sodium Metabisulphite:
Sodium Metabisulphite is produced industrially using two processes:
Dehydration of sodium hydrogen sulphite (heating or vacuum drying):
Water is removed and Sodium Metabisulphite is formed
Reaction of sodium sulphite with sulphur dioxide:
SO2 is passed through an aqueous sodium sulphite solution, causing Sodium Metabisulphite to precipitate
Chemical Structure of Sodium Metabisulphite:
The anion metabisulfite consists of an SO2 group linked to an SO3 group, with the negative charge more localised 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.
Reactivity of Sodium Metabisulphite:
Upon dissolution in water, bisulfite is generated:
Na2S2O5 + H2O → 2 Na+ + 2 HSO3−
History of Sodium Metabisulphite:
Sodium metabisulphite has its origins in the early development of sulfur-based preservation techniques, which date back to ancient civilizations.
Sulfur dioxide (SO₂), the active component derived from sodium metabisulphite, was historically used by the Greeks and Romans to preserve wine and disinfect containers due to its antimicrobial and antioxidant properties.
During the 18th and 19th centuries, advances in chemistry allowed scientists to better understand sulfur compounds and their reactions.
This led to the development of more stable and transportable forms of sulfur dioxide, including sulfites and metabisulfites.
Sodium metabisulphite emerged as a convenient solid form that could release SO₂ when dissolved in water or exposed to acidic conditions.
In the late 19th and early 20th centuries, sodium metabisulphite became widely adopted in the food and beverage industry, particularly in winemaking and brewing, where it was used to control fermentation and prevent spoilage.
Sodium metabisulphite's effectiveness in inhibiting microbial growth and oxidation made it a key additive in preserving quality and extending shelf life.
Over time, Sodium metabisulphite's applications expanded beyond food into water treatment, textile processing, and paper manufacturing.
With the rise of industrial chemistry in the 20th century, sodium metabisulphite became an important reducing agent and bleaching chemical.
Today, sodium metabisulphite remains widely used across multiple industries, although its use in food is regulated due to potential allergic reactions in sensitive individuals, particularly those with sulfite sensitivity or asthma.
Stability and Reactivity of Sodium Metabisulphite:
Chemical stability:
Stable under normal, dry storage conditions.
Reactivity:
Strong reducing agent.
Reacts with oxidizing agents.
Reacts with acids.
Reacts with moisture.
Conditions to avoid:
Heat.
Humidity.
Moisture.
Acidic conditions.
Incompatible materials:
Strong oxidizers.
Strong acids.
Nitrates.
Hazardous decomposition products:
Sulfur dioxide (SO₂) may be released.
Sulfur oxides may form.
Sodium oxides may be generated.
Handling and Storage of Sodium Metabisulphite:
Handling:
Avoid inhalation of dust.
Avoid contact with eyes and skin.
Use adequate ventilation.
Storage:
Store in a cool, dry, and well-ventilated place.
Keep container tightly closed.
Protect from moisture.
First Aid Measures of Sodium Metabisulphite:
Inhalation:
Move to fresh air.
Seek medical attention if symptoms persist.
Skin contact:
Wash with soap and water.
Eye contact:
Rinse cautiously with water for several minutes.
Seek medical attention if irritation continues.
Ingestion:
Rinse mouth.
Do not induce vomiting.
Seek medical advice immediately.
Firefighting Measures of Sodium Metabisulphite:
Suitable extinguishing media:
Use media appropriate for the surrounding fire.
Hazards:
Not highly flammable.
May release toxic sulfur dioxide fumes when heated.
Protective equipment:
Use self-contained breathing apparatus.
Wear protective clothing.
Accidental Release Measures of Sodium Metabisulphite:
Personal precautions:
Avoid dust formation.
Avoid inhalation.
Use appropriate personal protective equipment.
Environmental precautions:
Prevent entry into drains and waterways.
Methods for cleaning up:
Sweep up carefully.
Place in suitable containers.
Avoid generating dust.
Exposure Controls / Personal Protection of Sodium Metabisulphite:
Engineering controls:
Provide adequate ventilation.
Respiratory protection:
Use dust mask or respirator if needed.
Hand protection:
Wear chemical-resistant gloves.
Eye protection:
Use safety goggles.
Skin protection:
Wear protective clothing.
Identifiers of Sodium Metabisulphite:
Chemical formula: Na₂S₂O₅
Molecular weight: 190.10 g/mol
CAS number: 7681-57-4
EC number: 231-673-0
Chemical family: Inorganic sulfite / reducing agent
Appearance: White to slightly yellow crystalline powder
Odor: Pungent sulfur dioxide (SO₂) odor
Linear Formula: Na2S2O5
CAS Number: 7681-57-4
Molecular Weight: 190.11
EC Number: 231-673-0
CAS Number: 7681-57-4
ChEBI: CHEBI:114786
ChEMBL: ChEMBL2016976
ChemSpider: 571015
ECHA InfoCard: 100.028.794
EC Number: 231-673-0
E number: E223 (preservatives)
KEGG: D02054
PubChem CID: 656671
RTECS number: UX8225000
UNII: 4VON5FNS3C
UN number: 1759
CompTox Dashboard (EPA): : DTXSID0029684
InChI: Key: HRZFUMHJMZEROT-UHFFFAOYSA-L
InChI=1S/2Na.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2
SMILES: [O-]S(=O)S(=O)(=O)[O-].[Na+].[Na+]
Article No.: 05937
Grade: AR/ACS
Purity: 97%
CAS No.: 7681-57-4
Molecular Formula: Na2S2O5
Molecular Weight: 190.10
H.S. Code: 2832.1090
Shelf Life: 60 Months
Properties of Sodium Metabisulphite:
Chemical formula: Na2S2O5
Molar mass: 190.107 g/mol
Appearance: White to yellow powder
Odor: Faint SO2
Density: 1.48 g/cm3
Melting point: 170 °C (338 °F; 443 K) decomposition begins at 150 °C
Solubility in water:
45.1 g/100 mL (0 °C)
65.3 g/100 mL (20 °C)
81.7 g 100 mL (100 °C)
Solubility: Very soluble in glycerol
Slightly soluble in ethanol
Physical state at 20 °C: Solid
Colour: White crystalline
Odour: Sulphorous
pH value: 4.5 at 50 g/l at 20 °C
Melting point/ Freezing point [°C]: 300 °C
Density [g/cm3]: 1.48
Solubility in water [% weight]: 650 g/l at 20 °C
Partition coefficient Log Pow octanol / water at 20°C: -3.7
Physical state: Solid
Appearance: White to slightly yellow crystalline powder
Odor: Pungent sulfur dioxide (SO₂) odor
Chemical formula: Na₂S₂O₅
Molecular weight: 190.10 g/mol
Density: ~1.48 g/cm³
Melting point: ~150 °C
Boiling point: Not applicable
Solubility in water: Highly soluble
Solubility in organic solvents: Slightly soluble or insoluble
pH (aqueous solution): ~4–5 (acidic)
Hygroscopicity: Slightly hygroscopic
Specifications of Sodium Metabisulphite:
Appearance: White crystalline powder
Assay: Min. 97.0%
Insoluble matter in water: Max. 0.005%
Chloride (Cl): Max. 0.005%
Arsenic (As): Max. 0.0001%
Phosphate (PO4): Max. 0.002%
Thiosulphate (S2O3): Max. 0.05%
Heavy metal (as Pb): Max. 0.001%
Iron (Fe): Max. 0.002%
Related Compounds of Sodium Metabisulphite:
Sodium dithionite
Sodium thiosulfate
Sodium sulfate
Other anions:
Sodium sulfite
Sodium bisulfite
Other cations:
Potassium metabisulfite
Names of Sodium Metabisulphite:
Other names:
Sodium pyrosulfite
Sodium disulfite
