Sodium chlorate

Sodium chlorate
IUPAC name Sodium chlorate
Other names Sodium chlorate(V)
Identifiers
CAS number	7775-09-9 Y
PubChem	24487 Y
ChemSpider	22895 Y
UNII	T95DR77GMR Y
EC number	231-887-4
UN number	1495, 2428
KEGG	C18765 Y
MeSH	Sodium+chlorate
RTECS number	FO0525000
Jmol-3D images	Image 1
SMILES [Na+].[O-]Cl(=O)=O
InChI InChI=1S/ClHO3.Na/c2-1(3)4;/h(H,2,3,4);/q;+1/p-1 Y Key: YZHUMGUJCQRKBT-UHFFFAOYSA-M Y InChI=1S/ClHO3.Na/c2-1(3)4;/h(H,2,3,4);/q;+1/p-1 Key: YZHUMGUJCQRKBT-UHFFFAOYSA-M InChI=1/ClHO3.Na/c2-1(3)4;/h(H,2,3,4);/q;+1/p-1 Key: YZHUMGUJCQRKBT-REWHXWOFAH
Properties
Molecular formula	NaClO3
Molar mass	106.44 g/mol
Appearance	white solid
Odor	odorless
Density	2.5 g/cm3
Melting point	248 °C, 521 K, 478 °F
Boiling point	~300 °C decomp.
Solubility in water	101.0 g/100 mL (20 °C)
Refractive index (nD)	1.572
Hazards
MSDS	ICSC 1117
EU Index	017-005-00-9
EU classification	Oxidant (O) Harmful (Xn) Dangerous for the environment (N)
R-phrases	R9, R22, R51/53
S-phrases	(S2), S13, S17, S46, S61
NFPA 704	0 1 1 OX
Flash point	none
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
Y chlorate (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium chlorate is a chemical compound with the chemical formula (NaClO₃). 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. In September 2009, wholesale of sodium chlorate weedkiller was banned in all EU countries,^{[citation needed]} but consumers were allowed to use and store the product until May 2010.

Synthesis

Industrially, sodium chlorate is synthesized from the electrolysis of a hot sodium chloride solution in a mixed electrode tank:

NaCl + 3H₂O → NaClO₃ + 3H₂

It can also be synthesized by passing chlorine gas into a hot sodium hydroxide solution. 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.

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
• 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:

• Cotton
• Safflower
• Corn
• Flax
• Peppers
• Soybeans
• Grain sorghum
• Southern peas
• Dry beans
• Rice
• Sunflowers

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 by catalytic decomposition of sodium chlorate. The catalyst is normally iron powder. Barium peroxide (BaO₂) is used to absorb the chlorine which is a minor product in the decomposition.^[1] Iron powder is mixed with sodium chlorate and ignited by a charge which is activated by pulling on the emergency mask. The reaction produces more oxygen than is required for combustion. 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.^[2] The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.^[3]

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, that is other herbicides, sulfur, phosphorus, powdered metals, strong acids. Particularly when mixed with sugar it has explosive properties. If accidentally mixed with one of these substances it should not be stored in human dwellings.^[4]

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 an 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"^[5][6] about accidents with sodium chlorate when used as an herbicide to control ragwort in the 1930s.^[7] This later won him an Ig Nobel Prize in 2005,^[8] and was the basis for the May 2006 "Exploding Pants" episode of MythBusters.

References

1. ^ Yunchang Zhang, Girish Kshirsagar, and 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. 
2. ^ 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 441312. PMID 14897900. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=441312. 
3. ^ Goldfrank's Toxicologic Emergencies, McGraw-Hill Professional; 8th edition (March 28, 2006), ISBN 978-0071437639
4. ^ Beveridge, Alexander (1998). Forensic Investigation of Explosions. Taylor & Francis Ltd. ISBN 0-7484-0565-8. 
5. ^ "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
6. ^ "Histories: Farmer Buckley's exploding trousers", New Scientist
7. ^ "Trousers Explode, Evening Post, 21 April 1933
8. ^ 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

• International Chemical Safety Card 1117