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Und damit ist wohl klar, woher der Schwefel kommt... Vielleicht ist es auch nicht soo klar? - Kann mich gerade nicht entscheiden, was unter "klar" zu verstehen wäre...Römpp hat geschrieben:Die technische Herstellung erfolgt durch Umsetzung von Calciumcyanamid (Kalkstickstoff) mit Schwefelwasserstoff oder Schwefelwasserstoff liefernden Verbindungen.
Ob es etwas mehr Eisenthiocyanat oder zumindest teilweise isothiocyanat (und noch etwas Calciumcarbonat oder so drin hat?Ullmann hat geschrieben: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.
In Germany, thiourea is produced in a closed system by reaction of calcium cyanamide with 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. The converted reaction mixture is removed continuously from the reactor and excess H2S is removed by stripping. Waste-gas from the reactor contains hydrogen sulfide, which is purified in a scrubber connected to the reactor.
The stripped thiourea solution is filtered to remove the precipitated calcium carbonate formed as one of the reaction products. The filtrate is evaporated in vacuum and thiourea is crystallized by cooling. It is filtered, washed, and dried in an air stream.
The German producer gives the following specification for the standard product:
Thiourea ≥ 99.0 %
Water ≤ 0.30 %
Ash ≤ 0.10 %
Rhodanide (SCN–) ≤ 0.15 %
Other N- containing compounds ≤ 0.5 %
Iron ≤ 10 mg/kg
Auch nicht gerade aufschlussreich...Ullmann hat geschrieben:Calcium cyanamide is produced from calcium carbide and nitrogen gas by an exothermic solid nitrogenation at 1000°C. It is used as a slow release nitrogen fertilizer with beneficial side effects against soilborne deseases. In chemical industry, it is the base for cyanamide and thiourea chemistry.
Cyanamide is a fairly stable, toxic substance obtained from calcium cyanamide by reaction with water and carbon dioxide. It has vast applications in industrial nitrogen organic chemistry, and is also directly used as a plant protection agent.
Industrial-grade calcium cyanamide contains, in addition to CaCN2, ca. 20 % CaO and 10 – 12 % free carbon, which gives the product its gray-black color. It also contains a small amount of nitrides formed from silica and alumina. The total nitrogen content varies from 22 to 25 %, depending on the raw materials used. Of the total nitrogen, 92 – 95 % is present as cyanamide and 0.1 – 0.4 % as dicyandiamide; the remainder is present as nitrides.
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