Sodium chlorate is an inorganic compound with the chemical formula NaClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leave sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching paper.
Unit cell of sodium chlorate
3D model (JSmol)
|UN number||1495, 2428|
CompTox Dashboard (EPA)
|Molar mass||106.44 g mol−1|
|Appearance||Colorless or white solid, hygroscopic|
|Density||2.49 g/cm3 (15 °C)|
2.54 g/cm3 (20.2 °C)
|Melting point||248–261 °C (478–502 °F; 521–534 K)|
|Boiling point|| 300–400 °C (572–752 °F; 573–673 K) |
|79 g/100 mL (0 °C)|
89 g/100 mL (10 °C)
105.7 g/100 mL (25 °C)
125 g/100 mL (40 °C)
220.4 g/100 mL (100 °C)
|Solubility||Soluble in glycerol, hydrazine, methanol|
Slightly soluble in ethanol, ammonia
|Solubility in acetone||Sparingly soluble|
|Solubility in glycerol||20 g/100 g (15.5 °C)|
|Solubility in ethanol||14.7 g/100 g|
|Vapor pressure||<0.35 mPa|
Refractive index (nD)
|1.515 (20 °C)|
a = 6.57584 Å
Formula units (Z)
Heat capacity (C)
Std enthalpy of
Gibbs free energy (ΔfG˚)
|Safety data sheet||ICSC 1117|
|GHS Signal word||Danger|
|H271, H302, H411|
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|6500 mg/kg (rats, oral)|
700 mg/kg (dogs, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Industrially, sodium chlorate is produced by the electrolysis of a hot sodium chloride solution:
- NaCl + 3 H2O → NaClO3 + 3 H2:
The sodium chlorate process is not to be confused with the Chloralkali process, which is an industrial process for the electrolytic production of sodium hydroxide and chlorine gas.
The main commercial use for sodium chlorate is for making chlorine dioxide (ClO2). The largest application of ClO2, which accounts for about 95% of the use of chlorate, is in bleaching of pulp. All perchlorate compounds are produced industrially by the oxidation of solutions of sodium chlorate by electrolysis.
Sodium chlorate may be used to control a variety of plants including morning glory, canada thistle, johnson grass, bamboo, Ragwort, and St John's wort. The herbicide is mainly used on non-crop land for spot treatment and for total vegetation control on areas including roadsides, fenceways, and ditches. Sodium chlorate is also used as a defoliant and desiccant for:
If used in combination with atrazine, it increases the persistence of the effect. If used in combination with 2,4-D, performance is improved. Sodium chlorate has a soil sterilant effect. Mixing with other herbicides in aqueous solution is possible to some extent, so long as they are not susceptible to oxidation.
Chemical oxygen generation
Chemical oxygen generators, such as those in commercial aircraft, provide emergency oxygen to passengers to protect them from drops in cabin pressure. Oxygen is generated by high-temperature decomposition of sodium chlorate:
- 2 NaClO3 → 2 NaCl + 3 O2
Heat required to initiate this reaction is generated by oxidation of a small amount of iron powder mixed with the sodium chlorate, and the reaction consumes less oxygen than is produced. Barium peroxide (BaO2) is used to absorb the chlorine that is a minor product in the decomposition. An ignitor charge is activated by pulling on the emergency mask. Similarly, the Solidox welding system used pellets of sodium chlorate mixed with combustible fibers to generate oxygen.
Toxicity in humans
Due to its oxidative nature, sodium chlorate can be very toxic if ingested. The oxidative effect on hemoglobin leads to methaemoglobin formation, which is followed by denaturation of the globin protein and a cross-linking of erythrocyte membrane proteins with resultant damage to the membrane enzymes. This leads to increased permeability of the membrane, and severe hemolysis. The denaturation of hemoglobin overwhelms the capacity of the G6PD metabolic pathway. In addition, this enzyme is directly denatured by chlorate reducing its activity.
Therapy with ascorbic acid and methylene blue are frequently used in the treatment of methemoglobinemia. However, since methylene blue requires the presence of NADPH that requires normal functioning of G6PD system, it is less effective than in other conditions characterized by hemoglobin oxidation.
Acute severe hemolysis results, with multi-organ failure, including DIC and renal failure. In addition there is a direct toxicity to the proximal renal tubule. The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.
Sodium chlorate comes in dust, spray and granule formulations. There is a risk of fire and explosion in dry mixtures with other substances, especially organic materials, and other herbicides, sulfur, phosphorus, powdered metals, and strong acids. In particular, when mixed with sugar, it has explosive properties. If accidentally mixed with one of these substances it should not be stored in dwellings.
Marketed formulations contain a fire retardant, but this has little effect if deliberately ignited. Most commercially available chlorate weedkillers contain approximately 53% sodium chlorate with the balance being a fire depressant such as sodium metaborate or ammonium phosphates.
Sodium chlorate is the active ingredient in a variety of commercial herbicides. Some trade names for products containing sodium chlorate include Atlacide, Defol, De-Fol-Ate, Drop-Leaf, Fall, Harvest-Aid, Kusatol, Leafex, and Tumbleaf. The compound may be used in combination with other herbicides such as atrazine, 2,4-D, bromacil, diuron, and sodium metaborate.
Sodium chlorate was an extensively used weed killer within the EU, until 2009 when it was withdrawn after a decision made under terms of EU Regulations. Its use as a herbicide outside the EU remains unaffected, as does its use in other non-herbicidal applications, such as in the production of chlorine dioxide biocides and for pulp and paper bleaching.
Historian James Watson of Massey University in New Zealand wrote a widely reported article, "The Significance of Mr. Richard Buckley's Exploding Trousers" about accidents with sodium chlorate when used as a herbicide to control ragwort in the 1930s. This later won him an Ig Nobel Prize in 2005, and was the basis for the May 2006 "Exploding Pants" episode of MythBusters.
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