Preparation of Thiourea :
Numerous methods have already been proposed for the manufacture of thiourea by the treatment of an alkaline earth metal salt of cyanamide, such as calcium cyanamide, in the presence or absence of water with hydrogen sulfide or an alkaline earth metal sulfide, as calcium or barium sulfide and an agent such as carbonic acid, phosphoric acid, sulfuric acid or the like which decompose to form hydrogen sulfide and an insoluble alkaline earth metal salt. The reaction has been conducted at elevated and at ordinary temperatures and with or without the application of pressure.
Its preparation methods is barium sulfide reaction with sulfuric acid or hydrochloric acid, hydrogen sulfide gas by lime milk, negative pressure absorbing hydrogen sulfide was calcium solution reacts with calcium cyanamide, sulfur, calcium hydroxide and calcium cyanamide mole ratio is 1:5, under stirring constantly, the reaction temperature for 80 + 5 ℃, reaction time is 3 h, the negative pressure filter, the thiourea can generate liquid, then through evaporation, filtration, cooling, crystallization, a quick crystal thiourea, centrifugal dehydration for a quick finished products.
Reaction equation, such as: