Sodium chlorite
[CAS# 7758-19-2]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Metal halides and halides >> Metal chlorides and salts
• Name: Sodium chlorite
• Molecular Formula: NaClO₂
• Molecular Weight: 90.44
• CAS Registry Number: 7758-19-2
• EC Number: 231-836-6
• SMILES: [O-]Cl=O.[Na+]

Properties

• Melting point: 180-200 °C
• Water solubility: 39 g/100 mL (17 °C)

Safety Data

• Hazard Symbols: GHS03;GHS05;GHS06;GHS08;GHS09 Danger
• Risk Statements: H271-H272-H301-H310-H314-H318-H373-H400-H410-H412
• Safety Statements: P210-P220-P260-P262-P264-P264+P265-P270-P273-P280-P283-P301+P316-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P354+P338-P306+P360-P316-P317-P319-P321-P330-P361+P364-P363-P370+P378-P371+P380+P375-P391-P405-P420-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Acute toxicity	Acute Tox.	3	H301
Skin corrosion	Skin Corr.	1B	H314
Acute toxicity	Acute Tox.	2	H310
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Serious eye damage	Eye Dam.	1	H318
Oxidising solids	Ox. Sol.	2	H272
Oxidising solids	Ox. Sol.	1	H271
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Acute toxicity	Acute Tox.	2	H330
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	3	H311
Oxidising liquids	Ox. Liq.	1	H271
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	4	H332
Skin irritation	Skin Irrit.	2	H315
Skin corrosion	Skin Corr.	1A	H314
Specific target organ toxicity - single exposure	STOT SE	3	H335
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	1	H310
Specific target organ toxicity - single exposure	STOT SE	2	H371
Acute toxicity	Acute Tox.	1	H330
Carcinogenicity	Carc.	1B	H350
Skin corrosion	Skin Corr.	1C	H314

• Transport Information: UN 1496; UN 1908

Discovery and Applications

Sodium chlorite (NaClO₂) is an inorganic chemical compound first synthesized in the 19th century as part of studies on chlorine oxides and their salts. It is a white to pale yellow crystalline powder that is highly soluble in water and serves as a stable source of chlorine dioxide (ClO₂), a strong oxidizing agent. Sodium chlorite is produced industrially by the reduction of sodium chlorate (NaClO₃) with sulfur dioxide in an alkaline medium, a process that allows controlled generation of the reactive chlorite anion.

The principal application of sodium chlorite is the generation of chlorine dioxide, which is used extensively as a disinfectant and bleaching agent. In water treatment, chlorine dioxide produced in situ from sodium chlorite effectively disinfects drinking water and wastewater by inactivating bacteria, viruses, and protozoa. Unlike chlorine, chlorine dioxide does not form significant amounts of trihalomethanes, making it a preferred oxidant in potable water systems. It is also used in cooling towers and industrial water systems to prevent microbial growth and biofilm formation.

In the paper and pulp industry, sodium chlorite is employed as a bleaching agent for wood pulp. Its oxidative action selectively removes lignin from pulp fibers while preserving cellulose integrity, enhancing the brightness and quality of paper products. The use of sodium chlorite in pulp bleaching has contributed to environmentally safer practices, as it reduces the need for chlorine gas and minimizes the formation of chlorinated organic byproducts.

Sodium chlorite also finds application in chemical synthesis. It is used in the preparation of various organic compounds, such as chlorinated intermediates, and as an oxidant in selective reactions. Its ability to release chlorine dioxide under controlled conditions makes it a versatile reagent for laboratory and industrial oxidation processes.

Safety and handling considerations are critical due to the oxidizing properties of sodium chlorite. It can react violently with combustible materials and strong reducing agents, posing a fire and explosion risk. Solutions of sodium chlorite are corrosive and can cause skin and eye irritation. Proper storage, handling, and dilution are essential to ensure safety in both industrial and laboratory contexts.

The discovery and industrial development of sodium chlorite have established it as a key chemical in disinfection, bleaching, and oxidation processes. Its ability to generate chlorine dioxide efficiently, combined with broad antimicrobial and oxidative activity, ensures its continued importance across water treatment, pulp and paper manufacturing, and chemical synthesis applications. Its versatility, stability, and controlled reactivity highlight its value as a practical and widely used chemical compound in modern industry.

References

2012. Radon in indoor concentrations and indoor concentrations of metal dust particles in museums and other public buildings. Environmental Geochemistry and Health, 34(6).
DOI: 10.1007/s10653-012-9497-4

2011. Mineralogy, morphology, and textural relationships in coatings on quartz grains in sediments in a quartz-sand aquifer. Journal of Contaminant Hydrology, 124(1-4).
DOI: 10.1016/j.jconhyd.2011.02.003

2008. Development of an online biosensor for in situ monitoring of chlorine dioxide gas disinfection efficacy. Applied Microbiology and Biotechnology, 78(4).
DOI: 10.1007/s00253-007-1334-9