Thiourea thiocarbamide

Thiourea (II) may be obtained from ammonium thiocyanate (I) by an isomeric change analogous to ammonium cyanate, but the equilibrium relationship is very different (compare Section 111,133)  

Between 140° and 180° equilibrium is set up at a fairly rapid rate, but only 25 per cent, of thiourea is present in the equilibrium mixture. The yield is therefore far from satisfactory. 

It is prepared commercially by treating cyanamide (from calcium cyanamide) with ammonium sulphide  

Place 50 g. of ammonium thiocyanate in a small round-bottomed flask and immerse a thermometer in the substance. Heat in an oil bath until the temperature rises to 170° and maintain it at this temperature for 1 hour. Allow the melt to cool and extract it with 60-70 ml. of hot water. Filter the solution and allow to cool when crude thiourea separates the unchanged ammonium thiocyanate remains in the solution. Filter off the crude product and recrystallise it from a little hot water. The yield of thiourea, m.p. 172°, is 8 g. 

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Hydrochloric acid/thiourea [thiocarbamide, CS(NH2)2], The procedure for cleaning iron oxides containing copper and copper oxides is the same as for cleaning iron oxides alone. A typical formulation is 5% HC1 with 2% thiourea, plus corrosion inhibitor, wetting agent, and antifoam. A complete removal of copper is required because the passivation process otherwise will not be effective. 

In 1884, Emerson-Reynolds reported deposition of PbS films by reaction between thiourea (thiocarbamide) and alkaline lead tartrate, where the metallic sulphide. .. became firmly attached as a specular layer to the sides of the vessel [6], A wide range of substrates, apart from that just mentioned (a glass beaker), was successfully used for this deposition porcelain, ebonite, iron, steel, and brass were specifically mentioned. Even more important, the deposits were very adherent, as quantified by their ability to withstand considerable friction with a wash-leather, and under this treatment take a fine polish. ... 

Thiourea (thiocarbamide), 3.0 g Sodium hydroxide, 6.0g Water to make 1.0 liter... 

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