HYDROGEN CYANIDE (HYDROCYANIC ACID)

Hydrogen cyanide is a highly toxic clear to pale blue liquid or gas with the odor of bitter almonds. It melts at -14 C and boils at 25.6 C. It is miscible in water or ethanol and is slightly soluble in ether. Its water solution, called hydrocyanic acid, is a weak acid. Hydrogen cyanide is mainly obtained by the reaction of ammonia with carbon monoxide (Andrussow process) or with natural gas (methane) in the presence of rhodium/platinum catalyst at approximately 1100 C. Very short contact time (milliseconds) is required to obtain the optimum yield and consequently a high operating temperature is required to reach equilibrium. It can be prepared also by the reaction of cyanide salts, e.g., calcium cyanide, with a strong acid (sulfuric acid). Hydrogen cyanide is obtained as a by-product from acrylonitrile production. But the portion is small. It is used as a fumigant in agriculture. The principal use of hydrogen cyanide is in the manufacturing of acrylates, synthetic fibers (as a starting material for nylon 66), plastics and cyanide salts, especially sodium cyanide to extract gold from ore. It is used in the manufacturing of organic chemicals; acrylonitrile, metal polishes, dyes, rodenticides, pesticides, synthetic fibers, plastics, and electroplating solutions.