Calcium Cyanamide

calcium cyanamide [′kal·sē·əm sī′an·ə‚mīd]

(inorganic chemistry)

CaCN₂In pure form, colorless rhombohedral crystals, the commercial form being a gray material containing 55-70% CaCN₂; used as a fertilizer, weed killer, and defoliant.

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Calcium Cyanamide 

CaCN₂, the calcium salt of cyanamide (H₂N—C≡N, the amide of cyanic acid). Calcium cyanam-ide is a colorless crystalline compound that is soluble in water. It has a melting point of ~1300°C.

Technical-grade calcium cyanamide, which is produced by heating calcium carbide in a stream of nitrogen at 1000°C, is a dark gray powder consisting mainly of calcium cyanamide and carbon; the calcium cyanamide content is 57–60 percent. At 1400°–1500°C, technical-grade calcium cyanamide combines with sodium chloride (NaCl) to form cyanide flux, which in the recent past was the major source of hydrocyanic acid and cyanide salts. The salt sodium cyanide was formed by the reaction 2CaCN₂ + 2C + 2NaCl ⇄ CaCl₂ + Ca(CN)₂ + 2NaCN. For a long time calcium cyanamide was used as a raw material in the production of melamine. Calcium cyanamide is toxic.

Calcium cyanamide is a nitrogenous fertilizer, a defoliant, and a herbicide. Fertilizer-grade calcium cyanamide, which has a nitrogen content of 18–22 percent, is effective in acidic and slightly basic soils when applied during autumn plowing. Calcium cyanamide is not used as a fertilizer in the USSR. It is used for the preharvest removal of leaves from cotton plants and for the elimination of shoots of orache, chickweed, daisies, shepherd’s purse, and other weeds from fields planted with grains and certain vegetables.