Thiourea is an organosulfur compound with the formula, CH4N2S. It has properties very different to that of urea even though their structures are very similar, with a sulfur atom instead of an oxygen atom. It is a lustrous, white crystalline compound and is soluble in water and polar organic solvents.
Thiourea is manufactured using calcium cyanamide and hydrogen sulfide. Aqueous suspension of calcium cyanamide and a mixture, consisting of hydrogen sulfide and carbon dioxide, are continuously added to the reaction vessel. Through the process of stripping, excess hydrogen sulfide was subsequently removed before the thiourea solution was filtered to remove precipitated calcium carbonate. The obtained filtrate was then evaporated using a rotary evaporator and thiourea crystallized on cooling.
Thiourea can be used to manufacture thiourea dioxide, which is used in textile dyes, synthetic organic dyes for cellulosics. Sulfur dyes work using an oxidation-reduction dyeing method and a common reduction agent used is sodium hydrosulfite. However, sodium hydrosulfite is poor in preserving stability and undergoes oxidative decomposition at a faster rate compared to thiourea dioxide. In addition, hydrosulfite produces a bad smelling gas, therefore, making thiourea dioxide a better option and choice as reducing agent.
Wastewater Treatment Industry
Thiourea dioxide has successfully replaced sodium hydrosulfite and sodium hypochlorite as decolourization agents and tackled wastewater pollution problems from the use of chlorine containing compounds. It is also more effective and efficient as compared to sodium hydrosulfite and sodium hypochlorite, as it is able to give brighter bleach by choosing a suitable using amount. Thiourea dioxide also rarely undergoes oxidative decomposition when exposed to air. Even so, it decomposes at a much slower rate than sodium hydrosulfite and sodium hypochlorite.