hydrogen cyanide, HCN, colorless, volatile, and extremely poisonous chemical compound whose vapors have a bitter almond odor. It melts at −14°C and boils at 26°C. It is miscible in all proportions with water or ethanol and is soluble in ether. Its water solution is a weak acid (see acids and bases) commonly known as hydrocyanic acid or prussic acid. Its salts are called cyanides. Hydrogen cyanide may be synthesized directly from ammonia and carbon monoxide or from ammonia, oxygen (or air), and natural gas. It is a byproduct of the production of coke from coal and is recovered (along with hydrogen sulfide) from coke-oven exhaust gases. It may also be prepared by reacting a cyanide salt, e.g., calcium cyanide, with a strong acid, e.g., sulfuric acid, or by thermal decomposition of formamide. Because impure hydrogen cyanide can undergo spontaneous explosive polymerization and decomposition, a small amount of stabilizer (usually phosphoric acid) is added to it. The principal use of hydrogen cyanide is in the manufacture of organic chemicals, e.g., acrylonitrile, methyl methacrylate, and adiponitrile, that are used in producing synthetic fibers and plastics. It is also used in the chemical laboratory, and is sometimes used in agriculture as a fumigant. Hydrogen cyanide is found in nature in some vegetable substances, e.g., bitter almond, peach stones, cherry and cherry laurel leaves, and sorghum; it is usually combined in glycoside molecules (see sugar) and is released when they are broken down by enzymes during metabolism.
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