Sodium chlorate

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[4] and leave sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching paper.[7]

Sodium chlorate

Unit cell of sodium chlorate
IUPAC name
Sodium chlorate
Other names
Sodium chlorate(V)
3D model (JSmol)
ECHA InfoCard 100.028.989
EC Number
  • 231-887-4
MeSH Sodium+chlorate
RTECS number
  • FO0525000
UN number 1495, 2428
Molar mass 106.44 g mol−1
Appearance Colorless or white solid, hygroscopic
Odor Odorless
Density 2.49 g/cm3 (15 °C)[1]
2.54 g/cm3 (20.2 °C)[2]
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)[3]
Solubility Soluble in glycerol, hydrazine, methanol
Slightly soluble in ethanol, ammonia[1]
Solubility in acetone Sparingly soluble[1]
Solubility in glycerol 20 g/100 g (15.5 °C)[1]
Solubility in ethanol 14.7 g/100 g[1]
Vapor pressure <0.35 mPa[2]
34.7·10−6 cm3/mol
1.515 (20 °C)[4]
a = 6.57584 Å
104.6 J/mol·K[1]
129.7 J/mol·K[1]
-365.4 kJ/mol[1]
-275 kJ/mol[1]
Safety data sheet ICSC 1117
GHS pictograms [6]
GHS Signal word Danger
H271, H302, H411[6]
P220, P273[6]
NFPA 704 (fire diamond)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
6500 mg/kg (rats, oral)
700 mg/kg (dogs, oral)[1]
Related compounds
Other anions
Sodium chloride
Sodium hypochlorite
Sodium chlorite
Sodium perchlorate
Sodium bromate
Sodium iodate
Other cations
Ammonium chlorate
Potassium chlorate
Barium chlorate
Related compounds
Chloric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references


Industrially, sodium chlorate is produced by the electrolysis of a hot sodium chloride solution:[7]

NaCl + 3 H2O → NaClO3 + 3 H2:

This reaction progresses in heat (at least 70 degrees Celsius), and controlled pH. In lower temperature or with high pH another reaction progresses: 2 NaCl + H2O → NaClO + NaCl + 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.

It can also be synthesized by passing chlorine gas through a solution of sodium hydroxide. It is then purified by crystallization.


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.[7]


Sodium chlorate is used as a non-selective herbicide. It is considered phytotoxic to all green plant parts. It can also kill through root absorption.

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.

The sale of sodium chlorate as a weedkiller was banned in the European Union in 2009, with existing stocks to be used within the following year.[8]

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:[9]

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.[10] 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.[11] The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.[12]


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.[13]

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.

Trade names

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.

Cultural references

Historian James Watson of Massey University in New Zealand wrote a widely reported article, "The Significance of Mr. Richard Buckley's Exploding Trousers"[14][15] about accidents with sodium chlorate when used as a herbicide to control ragwort in the 1930s.[16] This later won him an Ig Nobel Prize in 2005,[17] and was the basis for the May 2006 "Exploding Pants" episode of MythBusters.

See also


  2. "GPS Safety Summary of Sodium Chlorate" (PDF). Arkema. Retrieved 2014-05-25.
  3. Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand.
  4. CID 516902 from PubChem
  5. S. C. Abrahams, J. L. Bernstein (1977). "Remeasurement of Optically Active NaClO3 and NaBrO3". Acta Crystallographica. B33: 3601–3604. doi:10.1107/S0567740877011637.
  6. Sigma-Aldrich Co., Sodium chlorate. Retrieved on 2014-05-25.
  7. Helmut Vogt, Jan Balej, John E. Bennett, Peter Wintzer, Saeed Akbar Sheikh, Patrizio Gallone “Chlorine Oxides and Chlorine Oxygen Acids” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH. doi:10.1002/14356007.a06_483
  8. "Sodium chlorate banned by EC". Horticulture Week. 28 August 2008.
  9. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  10. Yunchang Zhang; Girish Kshirsagar & James C. Cannon (1993). "Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen". Ind. Eng. Chem. Res. 32 (5): 966–969. doi:10.1021/ie00017a028.
  12. Goldfrank's Toxicologic Emergencies, McGraw-Hill Professional; 8th edition (March 28, 2006), ISBN 978-0-07-143763-9
  13. Beveridge, Alexander (1998). Forensic Investigation of Explosions. Taylor & Francis Ltd. ISBN 0-7484-0565-8.
  14. "The Significance of Mr. Richard Buckley's Exploding Trousers: Reflections on an Aspect of Technological Change in New Zealand Dairy Farming between the World Wars" Archived 2013-10-23 at the Wayback Machine, Agricultural History magazine
  15. "Histories: Farmer Buckley's exploding trousers", New Scientist
  16. "Trousers Explode, Evening Post, 21 April 1933
  17. James Watson for "The Significance of Mr. Richard Buckley’s Exploding Trousers.",

Further reading

  • "Chlorate de potassium. Chlorate de sodium", Fiche toxicol. n° 217, Paris:Institut national de recherche et de sécurité, 2000. 4pp.
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