Sodium Chlorate (CAS: 7775-09-9)

odium chlorate is an inorganic compound with the chemical formula NaClO3. It is a white crystalline

powder that is readily soluble in water. It ishygroscopic. It decomposes above 300 °C to release oxygen

and leave sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching 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 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 chlorate.

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.

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. 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. The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.

Formulations

Sodium chlorate comes in dust, spray and granule formulations. There is a risk of fire and explosion in dry mixtures

with other substances, especiallyorganic 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 human dwellings.

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