Sodium Chlorate
Sodium chlorate is a white crystalline powder that is readily soluble in water.
Sodium chlorate is one of the essential chemicals used as a bleaching agent or a weed-killer bleach in the paper and pulp industry.
IUPAC name: Sodium chlorate
CAS no.: 7775-09-9
EC / List no.: 231-887-4
Mol. formula: ClHO3.Na
Other names: Sodium chlorate(V)
Identifiers
CAS Number: 7775-09-9
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)
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[1]
Vapor pressure: <0.35 mPa
Magnetic susceptibility (χ): −34.7·10−6 cm3/mol
Refractive index (nD): 1.515 (20 °C)
Sodium chlorate produces Elemental-Chlorine Free (ECF) paper products that greatly influence the masses.
Sodium chlorate is the primary bleaching agent producing chlorine-free chemical pulp (ECF).
Sodium chlorate is also used by many other industries as a specialty oxidant.
Several hundred million tons are produced annually, mainly for applications in bleaching pulp to produce high-brightness paper.
Sodium chlorate candles release oxygen when simply ignited, were used for emergency oxygen generation in Soviet space missions, and are still used for atmospheric regeneration in disabled submarines.
Sodium chlorate causes the leaves of plants like cotton, rice, sunflower, corn, and dry beans to fall when extensively applied as a defoliant
Sodium chlorate is used in the electronic sector to make oxidizing candles for aircraft and submarines.
The size of the market for sodium chlorate is further increased by the fact that chlorine candles are used to give oxygen when it is scarce.
These candles are a necessary part of all airplanes and submarines.
Furthermore, customers’ demand for high-quality packaging, tissue, and craft paper has increased over the past few years.
In the future, this will present growth prospects for the global sodium chlorate market.
Sodium chlorate is increasingly being used in a variety of industries due to its accessibility, simplicity of storage, and affordability.
Also, one key element anticipated to drive the global sodium chlorate market during the projected period is rising demand for use in the production of dyes and in the leather & tanning sector.
Synthesis of Sodium chlorate
Sodium chlorate is produced by the electrolysis of concentrated sodium chloride solutions.
All other processes are obsolete.
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.
The overall reaction can be simplified to the equation:
NaCl + 3 H2O → NaClO3 + 3 H2
First, chloride is oxidized to form intermediate hypochlorite, ClO−, which undergoes further oxidization 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:
Cl2 + H2O ⇋ HClO + H+ + Cl−
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:
3 ClO− + 1.5 H2O → ClO3− + 3 H+ + 2 Cl− + 0.75 O2
The autoxidation of hypochlorous acid in the bulk electrolyte proceeds according to the simplified overall equation:
3 HClO → ClO3− + 2 Cl− + 3 H+
It is preceded by the dissociation of a part of the hypochlorous acid involved:
HClO → ClO− + H+
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:
2 HClO + ClO− → ClO3− + 2 Cl− + 2 H+
In addition to anode distance, 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 optimized to favor autoxidation.
Chlorate formation at the anode is treated as a loss reaction and is minimized 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 Sodium Chlorate
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 chlorates are derived from sodium chlorate, usually by salt metathesis with the corresponding chloride.
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-cropland for spot treatment and for total vegetation control on areas including roadsides, freeways, and ditches.
Sodium chlorate is also used as a defoliant and desiccant for:
Corn
Cotton
Dry beans
Flax
Grain sorghum
Peppers
Rice
Safflower
Southern peas
Soybeans
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 an 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 the high-temperature decomposition of sodium chlorate:
2 NaClO3 → 2 NaCl + 3 O2
The heat required to initiate this reaction is generated by the oxidation of a small amount of iron powder mixed with 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.
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.
Organic synthesis
Sodium chlorate can be used with hydrochloric acid (or also sulfuric acid and sodium chloride, 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.
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.
Translated names
chloran(V) sodu (pl)
chlorate de sodium (fr)
chlorečnan sodný (cs)
chlorečnan sodný (sk)
clorat de sodiu (ro)
clorato de sodio (es)
clorato de sódio (pt)
clorato di sodio sodio clorato (it)
Naatriumkloraat (et)
natrijev klorat (hr)
natrijev klorat (sl)
natrio chloratas (lt)
natriumchloraat (nl)
natriumchlorat (da)
Natriumchlorat (de)
Natriumkloraatti (fi)
natriumklorat (no)
natriumklorat (sv)
nátrium-klorát (hu)
nātrija hlorāts (lv)
χλωρικό νάτριο (el)
натриев хлорат (bg)
IUPAC names
chlorate de sodium
Registration dossier
Natriumchlorat
SODIUM CHLORATE
Sodium Chlorate
Sodium chlorate
sodium chlorate
Sodium Chlorate
Sodium chlorate
sodium chlorate
sodium-chlorate-
sodium;chlorate
Trade names
ALPURE®
chlorate salt of sodium
Natrium chlorate
Sodium chlorate
sodium chlorate
Sodium chlorate solution