Thiourea

Thiourea is used in four main ways: as an intermediate in the production of thiourea dioxide for wool and textile processing (30%), in ore leaching (25%), in diazo papers (15%) and as a catalyst in fumaric acid synthesis (10%), the remainder has smaller areas of use.

Thiourea has a wide range of uses, e.g., for producing and modifying textile and dyeing auxiliaries, in the production and modification of synthetic resins, in repro technology, in the production of pharmaceuticals (sulfathiazoles, tetramisole, and cephalosporins), in the production of industrial cleaning agents (e.g., for photographic tanks and metal surfaces in general), for engraving metal surfaces, as an isomerization catalyst in the conversion of maleic to fumaric acid, in copper refining electrolysis, in electroplating (e.g., of copper), and as an antioxidant (e.g., in biochemistry).

Thiourea is a white crystalline solid, both naturally occurring and synthetic, that is soluble in water, ammonium thiocyanate solution and ethanol. In the past, it was used as a photographic toning agent, a component of hair preparations and a dry cleaning agent. Currently, it is only used in animal glue liquefiers and silver tarnish removers. When heated to decomposition, thiourea emits toxic fumes of nitrogen oxides and sulfur oxides. Long-term exposure of humans to thiourea may cause bone marrow damage, resulting in reduced levels of red blood cells, white blood cells and/or platelets. It is reasonably anticipated to be a human carcinogen. (NCI05)

Production of thiourea is now carried out by treating technical-grade calcium cyanamide (CaCN2) with hydrogen sulfide or one of its precursors, e.g., ammonium sulfide or calcium hydrogen sulfide [19]. The calcium cyanamide must contain at least 23% nitrogen and must be free from calcium carbide (CaC2), as otherwise explosive acetylene is liberated by water or hydrogen sulfide. ... A reaction vessel is charged continuously with an aqueous suspension of calcium cyanamide and a mixture of hydrogen sulfide and carbon dioxide, such that the above reactions go to completion.