Chlorine dioxide
[CAS# 10049-04-4]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Metal halides and halides >> Metal chlorides and salts
• Name: Chlorine dioxide
• Molecular Formula: ClO₂
• Molecular Weight: 67.45
• CAS Registry Number: 10049-04-4
• EC Number: 233-162-8
• SMILES: O=Cl=O

Properties

• Melting point: -58.9 ºC (Expl.)
• Boiling point: 11.1 ºC (Expl.)
• Water solubility: Soluble

Safety Data

• Hazard Symbols: GHS03;GHS04;GHS05;GHS06;GHS07;GHS09 Danger
• Hazard Statements: H270-H280-H301-H314-H318-H319-H330-H332-H400
• Precautionary Statements: P220-P244-P260-P261-P264-P264+P265-P270-P271-P273-P280-P284-P301+P316-P301+P330+P331-P302+P361+P354-P304+P340-P305+P351+P338-P305+P354+P338-P316-P317-P320-P321-P330-P337+P317-P363-P370+P376-P391-P403-P403+P233-P405-P410+P403-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Skin corrosion	Skin Corr.	1B	H314
Acute toxicity	Acute Tox.	3	H301
Serious eye damage	Eye Dam.	1	H318
Oxidising gases	Ox. Gas	1	H270
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	2	H330
Acute toxicity	Acute Tox.	4	H332
Gases under pressure (liquid)	Press. Gas (Liq.)		H280
Gases under pressure (compressed)	Press. Gas (Comp.)		H280
Explosives	Expl.	1.5	H205
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	1	H330
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411

• Transport Information: UN 9191
• Hazardous Chemical?: Yes

Discovory and Applicatios

Chlorine dioxide is a chemical compound with the formula ClO₂, consisting of one chlorine atom covalently bonded to two oxygen atoms. It is a yellow to reddish-yellow gas at room temperature, possessing a strong, distinctive odor similar to chlorine but less pungent. Chlorine dioxide was first discovered in the early 19th century through the reaction of sodium chlorite with chlorine gas. Its unique chemical properties and effectiveness as an oxidizing agent led to widespread investigation and use.

Chlorine dioxide is primarily known for its strong oxidizing and disinfecting properties. It is highly soluble in water and remains stable in aqueous solutions under controlled conditions, which makes it especially valuable for water treatment. Unlike chlorine, chlorine dioxide does not form chlorinated organic compounds to a significant extent, reducing the formation of potentially harmful disinfection by-products such as trihalomethanes. This has driven its adoption as an alternative disinfectant in municipal water supplies, wastewater treatment, and industrial processes.

Its applications extend beyond water treatment to include bleaching in the paper and pulp industry. Chlorine dioxide provides effective delignification and bleaching while minimizing damage to cellulose fibers, leading to higher-quality paper products and reduced environmental impact compared to traditional chlorine bleaching.

Chlorine dioxide is also used for sterilization and deodorization in food processing, healthcare facilities, and air treatment. Its ability to kill bacteria, viruses, and fungi at low concentrations makes it suitable for sanitizing surfaces and equipment. Furthermore, chlorine dioxide has been employed in controlling biofilms and microbial contamination in cooling towers and industrial water systems.

The compound is typically generated on-site due to its instability and explosive potential when stored as a pure gas. Common production methods involve chemical reactions between sodium chlorite and an acid or chlorine gas under controlled conditions. Due to its strong oxidizing nature, handling chlorine dioxide requires strict safety precautions to prevent accidental release, explosion, or exposure.

Chlorine dioxide’s molecular structure is characterized by an odd number of electrons, making it a free radical. This contributes to its high reactivity and selective oxidation mechanisms, differentiating it from other chlorine-based oxidants.

In summary, chlorine dioxide’s discovery and subsequent development have established it as a versatile and effective disinfectant and bleaching agent. Its applications in water treatment, paper bleaching, sterilization, and odor control leverage its strong oxidizing properties while reducing environmental and health risks associated with traditional chlorine use. Its continued use and study contribute to advancements in public health, industrial processing, and environmental protection.

References

1946. The Use of Chlorine Dioxide in Water Treatment. American Journal of Public Health and the Nation's Health, 36(9).
DOI: 10.2105/ajph.36.9.1035

2024. Chlorine dioxide may be an alternative to acidification and chlorination for drinking water chemical disinfection in dairy beef bulls. Animal: An International Journal of Animal Bioscience, 18(9).
DOI: 10.1016/j.animal.2024.101244

2025. Large-scale dual-responsive ClO2 controlled-release film for strawberry preservation. Food Chemistry, 468.
DOI: 10.1016/j.foodchem.2024.141996