any one of a group of salts of chloric acid, HClO3. Chlorates are crystalline compounds that are stable at ordinary temperatures but decompose upon heating or in the presence of catalysts with the liberation of oxygen. Most are readily soluble in water and some organic solvents. Chlorates form explosive mixtures with organic and readily oxidizable compounds. Sodium chlorate, potassium chlorate, calcium chlorate, and magnesium chlorate are produced on an industrial scale.
Potassium chlorate, KClO3, has a density of 2.344 g/cm3 and a melting point of 370°C. It was first produced in 1786 by C. L. Berthollet by the addition of chlorine to a concentrated solution of potassium hydroxide. Its solubility in water is 32.4 g/liter (g/l) at 0°C, 170.5 g/l at 50°C, and 437 g/l at 100°C. Potassium chlorate is nonhygroscopic. It decomposes at about 400°C with the liberation of oxygen; however, in the presence of catalysts, such as MnO2 and Fe2O3, it decomposes at about 150°–200°C. Chemically pure potassium chlorate explodes at 550°–600°C, and in a mixture with sulfur, phosphorus, and many organic compounds, it explodes upon impact or friction. Its explosiveness increases in the presence of bromates and ammonium salts. Potassium chlorate is produced by the exchange decomposition of calcium chlorate or sodium chlorate with KCl. It is used in the production of matches and pyrotechnical substances.
Sodium chlorate, NaClO3, has a density of 2.49 g/cm3 at 15°C and a melting point of 248°C. Its solubility in water is 612 g/l at 0°C, 870 g/l at 50°C, and 1,190 at g/l at 100°C. Slightly hygroscopic, it is similar to potassium chlorate in chemical properties. It is produced by the electrolysis of aqueous solutions of NaCl in cells without diaphragms. It is used to obtain chlorine dioxide and in the production of other chlorates and perchlorates.
Calcium chlorate, Ca(ClO3)2, is a very hygroscopic salt. With water it forms the crystal hydrates Ca(ClO3) · nH2O, where n ranges from 1 to 6. It disperses in the air. Calcium chlorate is produced by the chlorination of milk of lime:
6Ca(OH)2 + 6Cl2 = Ca(ClO3)2 + 5CaCl2 + 6H2O
It is used as an intermediate in the production of potassium chlorate; it is also used in agriculture as a herbicide and defoliant.
Magnesium chlorate, Mg(ClO3)2, is a very hygroscopic salt. With water it forms crystal hydrates, such as Mg(ClO3)2 · 6H2O. Anhydrous magnesium chlorate has not been obtained. Magnesium chlorate disperses in the air. The crystal hydrate is obtained by melting sodium chlorate with bischofite:
2NaClO3 + MgCl2 · 6H2O = Mg(ClO3)2 · 6H2O + 2NaCl
It is flammable and explosive. Magnesium chlorate is used for the preharvest removal of leaves from the cotton plant and for the desiccation of sunflower, rice, seed plants of leguminous crops, and sugar-beet transplantations.
Chlorates have low toxicity. Chronic chlorate poisoning results from internal consumption or the breathing of chlorate dust.
L. M. IAKIMENKO