Sodium chlorate

Sodium chlorate (NaClO₃) is an oxidizing agent. It is mostly used to produce chlorine dioxide for bleaching paper pulp, but is also used as a herbicide and to prepare other chlorates. Production in the United States is about 441,000 tons per year.

When pure, it is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 250 °C to release oxygen and leave sodium chloride. It is synthesised from the electrolysis of hot sodium chloride solution in a mixed electrode tank. It can also be synthesised by passing chlorine gas to a hot sodium hydroxide solution. It is then purified by crystallization.

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Synthesis

Sodium chlorate can be created for laboratory use in small quantities by performing electrolysis on a solution of sodium chloride and water. The following reaction occurs:

NaCl + 3H₂O → NaClO₃ + 3H₂

For industrial production other methods are used.

Uses

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 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 roadsides, fenceways, ditches and suchlike. Sodium chlorate is also used as a defoliant and desiccant for cotton, safflower, corn, flax, peppers, soybeans, grain sorghum, southern peas, dry beans, rice and sunflowers. If used in combination with atrazine, it increases the persistence of the effect. If used in combination with 2,4-D, it improves performance of the material. 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.

Sodium chlorate is used in some aircraft as a source of supplemental oxygen. Iron powder is mixed with sodium chlorate and ignited by a charge activated by pulling on the emergency mask. The reaction produces more oxygen than is required for combustion.

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, that is other herbicides, sulfur, phosphorus, powdered metals, strong acids. Particularly when mixed with sugar it has explosive properties.^[1] The ease of availability of these two ingredients make it a common choice for home made bombs. Marketed formulations contain a fire depressant, 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

The active ingredient sodium chlorate is found 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. In the United Kingdom there are many brands of Sodium Chlorate Weedkillers. Two well known ones are Doff and Wilkinsons. In Italy it is found under the Zapi brand, sold as "Grasskiller Liquid".

Cultural References

• In the May 2006 Exploding Pants episode of MythBusters, Sodium Chlorate was used as the secret ingredient to explore the story of 1931 New Zealand farmers, such as Richard Buckley, whose trousers exploded or caught on fire, leading to a number of deaths.
• James Watson of Massey University in New Zealand won an Ig Nobel Prize for agricultural history in October 2005 for his research into the exploding trousers of the early 1930s in New Zealand..

See also

• Chloric acid

References

1. ^ Beveridge, Alexander (1998). Forensic Investigation of Explosions. Taylor & Francis Ltd. ISBN 0-7484-0565-8. 

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