Sodium chlorate

Sodium chlorate

Unit cell of sodium chlorate
Names
IUPAC name Sodium chlorate
Other names Sodium chlorate(V)
Identifiers
CAS Number	7775-09-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:65242 N
ChemSpider	22895 Y
ECHA InfoCard	100.028.989
EC Number	231-887-4
KEGG	C18765 Y
MeSH	Sodium+chlorate
PubChem CID	516902
RTECS number	FO0525000
UNII	T95DR77GMR Y
UN number	1495, 2428
CompTox Dashboard (EPA)	DTXSID7026025
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
SMILES [Na+].[O-]Cl(=O)=O
Properties
Chemical formula	NaClO3
Molar mass	106.44 g mol−1
Appearance	Colorless or white solid, hygroscopic
Odor	Odorless
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) decomposes
Solubility in water	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
Magnetic susceptibility (χ)	−34.7·10−6 cm3/mol
Refractive index (nD)	1.515 (20 °C)
Structure
Crystal structure	cubic
Point group	P213
Lattice constant	a = 6.57584 Å
Formula units (Z)	4
Thermochemistry
Heat capacity (C)	104.6 J/mol·K
Std molar entropy (S⦵298)	129.7 J/mol·K
Std enthalpy of formation (ΔfH⦵298)	-365.4 kJ/mol
Gibbs free energy (ΔfG⦵)	-275 kJ/mol
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H271, H302, H411
Precautionary statements	P220, P273
NFPA 704 (fire diamond)	2 0 3 OX
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	6500 mg/kg (rats, oral) 700 mg/kg (dogs, oral)
Safety data sheet (SDS)	ICSC 1117
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

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 leaves sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching pulp to produce high brightness paper.

Synthesis

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

NaCl + 3 H₂O → NaClO₃ + 3 H₂

This reaction progresses in heat (at least 70 °C), 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.

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.

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:

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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 citing health dangers, with existing stocks to be used within the following year.

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.

Oxygenless combustion

Sodium chlorate can be mixed with sucrose sugar to make a highly explosive fuel, similar to that of gunpowder, that burns in airtight spaces. This is the reaction:

8 NaClO₃ + C₁₂H₂₂O₁₁ → 8 NaCl + 12 CO₂ + 11 H₂O

However this sodium chlorate is mostly replaced by potassium chlorate.

Toxicity in humans

Sodium chlorate is toxic: "doses of a few grams of chlorate are lethal". 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.

Acute severe hemolysis results, with multi-organ failure, including DIC and kidney failure. In addition there is a direct toxicity to the proximal renal tubule. The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.

Formulations

Sodium chlorate comes in dust, spray and granule formulations. Mixtures of chlorates and organic compounds pose a severe risk of explosions

Marketed formulations contain a fire retardant. 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" 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.

See also

• Sodium chloride

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