Chlorine dioxide

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Chlorine dioxide
Chlorine dioxide.jpg
IUPAC name
Chlorine dioxide
Preferred IUPAC name
Chlorine dioxide
Systematic IUPAC name
Chlorine dioxide
Other names
Chlorine(IV) oxide
Chlorine peroxide
Jmol-3D images Image
Molar mass 67.45 g/mol
Appearance Yellow to orange gas
Odor Acrid
Density 2.757 g/L
Melting point −59 °C (−74 °F; 214 K)
Boiling point 11 °C (52 °F; 284 K)
8 g/L (at 20 °C)
Solubility Soluble in alkaline and sulfuric acid solutions
Vapor pressure >1 atm
Acidity (pKa) 3.0(5)
257.22 J·K−1·mol−1
104.60 kJ/mol
Safety data sheet Ecosense Company
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
292 mg/kg (oral, rat)
260 ppm (rat, 2 hr)
Related compounds
Related compounds
Dichlorine heptoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chlorine dioxide is a chemical compound with the formula ClO2.



Chlorine dioxide does not hydrolyze when it is absorbed in water and remains a dissolved gas in solution. Chlorine dioxide is approximately 10 times more soluble in water than chlorine.

Chlorine dioxide has been known to spontaneously explode when exposed to sunlight/UV light.[1] It lacks an upper explosive limit, so it can explode under any concentration.


Chlorine dioxide is a yellowish gas, with an acrid odor, very reactive, very soluble in water.


Chlorine dioxide is not sold and has to be made in situ.


Chlorine dioxide is a compound that can decompose extremely violently when separated from diluting substances. As a result, preparation methods that involve producing solutions of it without going through a gas-phase stage are often preferred.[2]

In the laboratory, ClO2 can be prepared by oxidation of sodium chlorite with chlorine:

2 NaClO2 + Cl2 → 2 ClO2 + 2 NaCl

The addition of hydrochloric acid to sodium chlorite, in the presence of sodium hypochlorite, also yields this compound. The reaction will also work if only sodium chlorite and HCl alone are used.

2 NaClO2 + 2 HCl + NaOCl → 2 ClO2 + 3 NaCl + H2O
5 NaClO2 + 4 HCl → 5 NaCl + 4 ClO2 + 2 H2O

Chlorine dioxide can also be prepared also by reaction of potassium chlorate with oxalic acid:

2 KClO3 + 2 H2C2O4 → K2C2O4 + 2 ClO2 + 2 CO2 + H2O
2 KClO3 + H2C2O4 + 2 H2SO4 → 2 KHSO4 + 2 ClO2 + 2 CO2 + 2 H2O


  • Bleaching of wood pulp
  • Disinfection (water chlorination)
  • Oxidizer
  • Light sensitive reaction demonstration



Chlorine dioxide is highly reactive and corrosive. The gas can explode under the effect of sunlight if present in a transparent container. The United States Environmental Protection Agency has set a maximum level of 0.8 mg/L for chlorine dioxide in drinking water.


Chlorine dioxide cannot be safely stored. However, it can be easily made from sodium chlorite and acid.


The gaseous form should be released in the air in remote areas. Solutions can be neutralized with a reducing agent.



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