Sodium Metabisulphite

It is used as a preservative and antioxidant in food. It is used as a cleaning agent for potable water desalination systems and used to remove chloramine from drinking water after treatment.

Synonyms
Disodium Pyrosulfite, E 223, SMBS, Sodium Bisulfite Anhydrous, Sodium Disulfite, Sodium Hydrogen Sulfite, Sodium Pyrosulfite
Chemical Formula
Na2S2O5
CAS Number
7681-57-4

Characteristics

Molar Weight
190.095 g/mol
Melting Point
170 °C
Density
1.310 – 1.370 g/cc
Forms
Powder, White, Yellow

Uses and applications

Key applications

  • Hair care
  • Fabric, textile and leather products
  • Water treatment
  • Cleaning products
  • Preservative
  • Wine production
  • Pharmaceuticals
  • Laundry products
  • Building & Construction products

General information about Sodium Metabisulphite

Sodium Metabisulphite (Na2S2O5), also known as sodium pyrosulphite or sodium disulphite, is a sodium salt of disulphuric acid. The compound 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.
Properties of Sodium Metabisulphite
Sodium Metabisulphite is a whitish to yellowish crystalline powder with a pungent odour and a strong hygroscopic effect. In water, the compound 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. It oxidises to sodium sulphate in air and also decomposes when heated to form sodium sulphate and sulphur dioxide.
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

Sodium Metabisulphite in the food industry

Under the designation E 223, Sodium Metabisulphite is used in the food industry as a preservative and antioxidant. It extends shelf life, prevents discolouration and inhibits the growth of microorganisms. Typical applications include:
  • Dried fruit: prevents browning and ensures colour stability
  • Potato products: prevention of enzymatic darkening
  • Meat products: prevention of oxidative discolouration and microbial spoilage
  • Seafood: preservation of colour and delay of spoilage
  • Baked goods: Stabilising fats and improving storage stability
  • Fruit juices: Stabilising colour and preserving aroma
  • Beer: Reducing oxidative processes to ensure flavour stability
  • Wine (sulphurisation): Stabilising the fermentation process and protecting 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.
Aerial view of water treatment plant

Sodium Metabisulphite in water treatment

In water treatment applications, Sodium Metabisulphite is used to neutralise oxidising agents (chlorine, ozone). It 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.
Rolls of fabric and textiles in a factory shop or store or bazar. Multi different colors and patterns on the market. Industrial fabrics.

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.

Summary

Sodium Metabisulphite (sodium metabisulphite, E 223) is a versatile reducing agent, preservative, bleaching agent and antioxidant. It is widely used in the food, pharmaceutical, textile, leather, construction, cleaning and water treatment industries.
The compound is characterised by its reactive, strongly reducing nature and is therefore used in many technical, chemical and biological processes.