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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.[6]

Synthesis

Industrially, sodium chlorate is produced by the electrolysis of a hot sodium chloride solution:[6]

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 Chloralkali process is an industrial process for the electrolytic production of sodium hydroxide and chlorine.

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

Uses

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.[6]

Herbicides

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.

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. Heat 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 which is a minor product in the decomposition.[7] 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.[8] The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.[9]

Formulations

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.[10]

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 weedkiller within the EU, up 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"[11][12] about accidents with sodium chlorate when used as a herbicide to control ragwort in the 1930s.[13] This later won him an Ig Nobel Prize in 2005,[14] and was the basis for the May 2006 "Exploding Pants" episode of MythBusters.

See also

References

  1. ^ a b c d e f g h i j k http://chemister.ru/Database/properties-en.php?dbid=1&id=786
  2. ^ a b "GPS Safety Summary of Sodium Chlorate" (PDF). http://www.arkema.com. Arkema. Retrieved 2014-05-25.  External link in website= (help)
  3. ^ Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand. 
  4. ^ a b CID 516902 from PubChem
  5. ^ a b c Sigma-Aldrich Co., Sodium chlorate. Retrieved on 2014-05-25.
  6. ^ a b c 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
  7. ^ 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. 
  8. ^ Oliver J.; MacDowell M., Tracy A (1951). "THE PATHOGENESIS OF ACUTE RENAL FAILURE ASSOCIATED WITH TRAUMATIC AND TOXIC INJURY. RENAL ISCHEMIA, NEPHROTOXIC DAMAGE AND THE ISCHEMURIC EPISODE". J Clin Invest. 30 (12): 1307–439. doi:10.1172/JCI102550. PMC 441312Freely accessible. PMID 14897900. 
  9. ^ Goldfrank's Toxicologic Emergencies, McGraw-Hill Professional; 8th edition (March 28, 2006), ISBN 978-0-07-143763-9
  10. ^ Beveridge, Alexander (1998). Forensic Investigation of Explosions. Taylor & Francis Ltd. ISBN 0-7484-0565-8. 
  11. ^ "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", Agricultural History magazine
  12. ^ "Histories: Farmer Buckley's exploding trousers", New Scientist
  13. ^ "Trousers Explode, Evening Post, 21 April 1933
  14. ^ James Watson for "The Significance of Mr. Richard Buckley’s Exploding Trousers.", improbable.com

Further reading

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

External links