Sodium metabisulfite
[CAS# 7681-57-4]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Metal sulfides and sulfates
• Name: Sodium metabisulfite
• Synonyms: Sodium pyrosulfite; Disodium disulphite; Disulfurous acid disodium salt; Pyrosulfurous acid disodium salt
• Molecular Formula: Na₂S₂O₅
• Molecular Weight: 190.10
• CAS Registry Number: 7681-57-4
• EC Number: 231-673-0
• SMILES: [O-]S(=O)S(=O)(=O)[O-].[Na+].[Na+]

Properties

• Density: 1.48
• Melting point: 150 °C
• Water solubility: 540 g/L (20 °C)

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H302-H318
• Safety Statements: P264-P264+P265-P270-P280-P301+P317-P305+P354+P338-P317-P330-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	3	H301
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Specific target organ toxicity - single exposure	STOT SE	3	H335
Respiratory sensitization	Resp. Sens.	1	H334
Skin sensitization	Skin Sens.	1	H317

• Transport Information: UN 2693

Discovery and Applications

Sodium metabisulfite was first synthesized in the 19th century as a result of research into methods to stabilize and preserve food. It is a white crystalline powder composed of sodium, sulfur, and oxygen, produced by the reaction of sulfur dioxide (SO2) with sodium carbonate (Na2CO3), followed by evaporation and crystallization. Chemically, sodium metabisulfite contains two sulfite ions (SO3²?) connected by a sulfur-sulfur bond, making it efficient in releasing sulfur dioxide when dissolved in water.

Sodium metabisulfite is widely used as a preservative in the food and beverage industry. Its ability to release sulfur dioxide inhibits the growth of bacteria, fungi, and yeasts, thereby extending the shelf life of products such as dried fruits, juices, and wines. This antimicrobial effect helps maintain freshness and prevents spoilage, making sodium metabisulfite a key ingredient in food preservation. In addition to its preservative properties, sodium metabisulfite also acts as an antioxidant, which prevents oxidation of certain food ingredients. This function is essential for protecting the color, flavor, and nutritional value of foods, especially in processed foods and beverages. In the wine and beer industry, sodium metabisulfite is used to prevent oxidation and bacterial contamination. It helps stabilize the final product, ensuring consistency in taste and quality. It is often added at various stages of production, including bottling, to prevent spoilage and maintain desired organoleptic properties.

In the pharmaceutical industry, sodium metabisulfite is used as an antioxidant to prevent oxidative degradation of drugs. It helps stabilize active ingredients in a variety of formulations, including injectable drugs and topical creams, ensuring their efficacy and shelf life. Sodium metabisulfite is also used as a disinfectant in medical settings to sterilize equipment and surfaces, an effective way to reduce microbial contamination. Its ability to release sulfur dioxide allows it to be used to decontaminate and disinfect spaces where sterility is critical.

Sodium metabisulfite is used in water treatment plants for dechlorination, neutralizing residual chlorine and chloramines in treated water. This process is essential to prevent chlorine-related problems in downstream applications, such as in aquaculture, where chlorine can be harmful to fish and aquatic life. In wastewater treatment, sodium metabisulfite is used to remove dissolved oxygen from water and prevent corrosion in water pipes and storage systems. This application helps manage water safety in industrial processes and municipal water systems.

Sodium metabisulfite is used in the textile industry as a reducing agent in dyeing processes. It helps bleach and remove excess dye from fabrics, ensuring even coloring and improving the quality of finished textile products. In photographic processing, sodium metabisulfite is used in developing and fixing solutions to preserve the image and enhance its stability. Its reducing properties help control image development and ensure the desired chemical reactions. Sodium metabisulfite acts as a reducing agent in various chemical manufacturing processes. It is involved in the production of chemicals, pharmaceuticals, and even in the formulation of certain detergents, contributing to a variety of industrial applications.

References

2017. Control of Native Spoilage Yeast on Dealcoholized Red Wine by Preservatives Alone and in Binary Mixtures. Journal of Food Science, 82(8).
DOI: 10.1111/1750-3841.13817

1993. Effect of an inhaled histamine H3‐receptor agonist on airway responses to sodium metabisulphite in asthma. British Journal of Clinical Pharmacology, 35(1).
DOI: 10.1111/j.1365-2125.1993.tb05671.x

1986. Allergic reaction to sulfiting agents. Annals of Emergency Medicine, 15(1).
DOI: 10.1016/s0196-0644(86)80492-9