Sodium chlorate is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

Na ClO₃. It is a white

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

powder that is readily soluble in water. It is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...

. It decomposes above 300 °C to release

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

and leaves

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...

. Several hundred million tons are produced annually, mainly for applications in

bleach Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

ing pulp to produce high brightness

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distribu ...

Synthesis

Industrially, sodium chlorate is produced by the

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...

of concentrated sodium chloride solutions. All other processes are obsolete. The sodium chlorate process is not to be confused with the

chloralkali process The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are commodit ...

, which is an industrial process for the electrolytic production of sodium hydroxide and chlorine gas. The overall reaction can be simplified to the equation: First,

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

is oxidised to form intermediate

hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ...

, ClO⁻, which undergoes further oxidisation to chlorate along two competing reaction paths: (1) Anodic chlorate formation at the boundary layer between the electrolyte and the anode, and (2) Autoxidation of hypochlorite in the bulk electrolyte. Under electrolysis hydrogen and sodium hydroxide are formed at the cathode and chloride ions are discharged at the anode ( mixed metal oxide electrode is often used). The evolved chlorine does not escape as a gas but undergoes hydrolysis: The hydrolysis of chlorine is considered to be fast. The formation of H⁺ ions should make the boundary layer at the anode strongly acidic and this is observed at low chloride concentrations. However, large concentrations of chloride, as they occur in industrial chlorate cells, shift the hydrolysis equilibrium to the left. At the boundary layer the concentration of H⁺ is not high enough to permit diffusion into the bulk electrolyte. Therefore hydrogen is transported away from the anode mostly as hypochlorous acid rather than H⁺. The hypochlorous acid dissociates in the bulk electrolyte where the pH is high and the hypochlorite ion diffuses back to the anode. More than two thirds of the hypochlorite is consumed by buffering before reaching the anode. The remainder is discharged at the anode to form chlorate and oxygen: The autoxidation of hypochlorous acid in the bulk electrolyte proceeds according to the simplified overall equation: It is preceded by the dissociation of a part of the hypochlorous acid involved: The reaction requires a certain distance from the anode to occur to a significant degree, where the electrolyte is sufficiently buffered by the hydroxyl formed at the cathode. The hypochlorite then reacts with the rest of the acid: In addition to anode distance the autoxidation also depends on temperature and pH. A typical cell operates at temperatures between 80 °C and 90 °C and at a pH of 6.1–6.4. Independent of the reaction route the discharge of 6 mol of chloride is required to yield 1 mol of chlorate. However, the anodic oxidation route requires 50% additional electric energy. Therefore, industrial cells are optimised to favour autoxidation. Chlorate formation at the anode is treated as a loss reaction and is minimised by design. Other loss reactions also decrease the current efficiency and must be suppressed in industrial systems. The main loss occurs by the back reduction of hypochlorite at the cathode. The reaction is suppressed by the addition of a small amount of dichromate (1–5 g/L) to the electrolyte. A porous film of chromium hydroxide is formed by cathodic deposition. The film impedes the diffusion of anions to the cathode, whereas the access of cations and their reduction is facilitated. The film stops growing on its own after it reaches a certain thickness.

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 other, less important

chlorate The chlorate anion has the formula ClO3-. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by ...

s are derived from sodium chlorate, usually by

salt metathesis A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding a ...

with the corresponding chloride. All

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. ...

compounds are produced industrially by the oxidation of solutions of sodium chlorate by electrolysis.

Herbicides

Sodium chlorate is used as a non-selective

herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

. 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 Morning glory (also written as morning-glory) is the common name for over 1,000 species of flowering plants in the family Convolvulaceae, whose current taxonomy and systematics are in flux. Morning glory species belong to many genera, some of ...

, canada thistle,

johnson grass Johnson grass or Johnsongrass, ''Sorghum halepense'', is a plant in the grass family, Poaceae, native to Asia and northern Africa. The plant has been introduced to all continents except Antarctica, and most larger islands and archipelagos. It re ...

bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...

, 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 A defoliant is any herbicidal chemical sprayed or dusted on plants to cause their leaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, along with the ...

and

desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccants ...

for: *

Corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...

Cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...

*Dry beans *

Flax Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known in ...

*Grain

sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many other ...

Peppers Pepper or peppers may refer to: Food and spice * Piperaceae or the pepper family, a large family of flowering plant ** Black pepper * ''Capsicum'' or pepper, a genus of flowering plants in the nightshade family Solanaceae ** Bell pepper ** Chili ...

Rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

Safflower Safflower (''Carthamus tinctorius'') is a highly branched, herbaceous, thistle-like annual plant in the family Asteraceae. It is commercially cultivated for vegetable oil extracted from the seeds and was used by the early Spanish colonies along ...

*Southern peas *

Soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...

s *

Sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), ...

s If used in combination with

atrazine Atrazine is a chlorinated herbicide of the triazine class. It is used to prevent pre-emergence broadleaf weeds in crops such as maize (corn), soybean and sugarcane and on turf, such as golf courses and residential lawns. Atrazine's primary m ...

, 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 generator A chemical oxygen generator is a device that releases oxygen via a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate; ozonides are a promising group of oxygen sources. The generators are usually ig ...

s, 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 required to initiate this reaction is generated by

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

of a small amount of iron powder mixed with the sodium chlorate, and the reaction consumes less oxygen than is produced. Barium peroxide ( Ba O₂) is used to absorb the

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

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 Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). T ...

, that burns in airtight spaces. This is the reaction: However this sodium chlorate is mostly replaced by

potassium chlorate Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. After sodium chlorate, it is the second most common chlorate in industrial use. ...

Organic synthesis

Sodium chlorate can be used with

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

(or also

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

and

, the reaction of which generates HCl) to chlorinate aromatic compounds without the use of organic solvents. In this case its function is to oxidize the HCl to obtain either HOCl or Cl₂ (depending upon the pH) in-situ which are the active chlorinating agents.

Toxicity in humans

Sodium chlorate is toxic: "doses of a few grams of chlorate are lethal". (ld50 oral in rat
1200mg
kg) The oxidative effect on

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythroc ...

leads to

methaemoglobin Methemoglobin (British: methaemoglobin) (pronounced "met-hemoglobin") is a hemoglobin ''in the form of metalloprotein'', in which the iron in the heme group is in the Fe3+ (ferric) state, not the Fe2+ (ferrous) of normal hemoglobin. Sometimes, it ...

formation, which is followed by denaturation of the

globin The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myogl ...

protein and a

cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

ing of

erythrocyte Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hol ...

membrane proteins with resultant damage to the membrane enzymes. This leads to increased permeability of the membrane, and severe

hemolysis Hemolysis or haemolysis (), also known by several other names, is the rupturing ( lysis) of red blood cells (erythrocytes) and the release of their contents ( cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in viv ...

. The denaturation of hemoglobin overwhelms the capacity of the

G6PD Glucose-6-phosphate dehydrogenase (G6PD or G6PDH) () is a cytosolic enzyme that catalyzes the chemical reaction : D-glucose 6-phosphate + NADP+ + H2O 6-phospho-D-glucono-1,5-lactone + NADPH + H+ This enzyme participates in the pentose phosp ...

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...

. In addition, this enzyme is directly denatured by chlorate. Acute severe hemolysis results, with

multi-organ failure Multiple organ dysfunction syndrome (MODS) is altered organ function in an acutely ill patient requiring medical intervention to achieve homeostasis. Although Irwin and Rippe cautioned in 2005 that the use of "multiple organ failure" or "multisy ...

, including DIC and

kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...

. In addition there is a direct toxicity to the proximal renal tubule. The treatment will consist of

exchange transfusion An exchange transfusion is a blood transfusion in which the patient's blood or components of it are exchanged with (replaced by) other blood or blood products. The patient's blood is removed and replaced by donated blood or blood components. This ...

peritoneal dialysis Peritoneal dialysis (PD) is a type of dialysis which uses the peritoneum in a person's abdomen as the membrane through which fluid and dissolved substances are exchanged with the blood. It is used to remove excess fluid, correct electrolyte pro ...

hemodialysis Hemodialysis, also spelled haemodialysis, or simply dialysis, is a process of purifying the blood of a person whose kidneys are not working normally. This type of dialysis achieves the extracorporeal removal of waste products such as creatinin ...

Formulations

Sodium chlorate comes in

dust Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in ...

spray Spray or spraying commonly refer to: * Spray (liquid drop) ** Aerosol spray ** Blood spray ** Hair spray ** Nasal spray ** Pepper spray ** PAVA spray ** Road spray or tire spray, road debris kicked up from a vehicle tire ** Sea spray, refers to ...

and granule formulations. Mixtures of chlorates and organic compounds pose a severe risk of explosions Marketed formulations contain a

fire retardant A fire retardant is a substance that is used to slow down or stop the spread of fire or reduce its intensity. This is commonly accomplished by chemical reactions that reduce the flammability of fuels or delay their combustion. Fire retardants ...

. Most commercially available chlorate weedkillers contain approximately 53% sodium chlorate with the balance being a fire depressant such as

sodium metaborate Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula . However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is or . The formula can be written also as · to highlight the ...

ammonium phosphate Ammonium phosphate is the inorganic compound with the formula (NH4)3PO4. It is the ammonium salt of orthophosphoric acid. A related "double salt", (NH4)3PO4.(NH4)2HPO4 is also recognized but is impractical use. Both triammonium salts evolve ammoni ...

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 Massey University ( mi, Te Kunenga ki Pūrehuroa) is a university based in Palmerston North, New Zealand, with significant campuses in Albany and Wellington. Massey University has approximately 30,883 students, 13,796 of whom are extramural o ...

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 The Ig Nobel Prize ( ) is a satiric prize awarded annually since 1991 to celebrate ten unusual or trivial achievements in scientific research. Its aim is to "honor achievements that first make people laugh, and then make them think." The name o ...

in 2005,James Watson for "The Significance of Mr. Richard Buckley’s Exploding Trousers."
improbable.com and was the basis for the May 2006 "Exploding Pants" episode of

MythBusters ''MythBusters'' is a science entertainment television program, developed by Peter Rees and produced by Australia's Beyond Television Productions. The series premiered on the Discovery Channel on January 23, 2003. It was broadcast internation ...

References

External links

International Chemical Safety Card 1117
{{DEFAULTSORT:Sodium Chlorate Chlorates Sodium compounds Desiccants Pyrotechnic oxidizers Oxidizing agents