UREA
UREA
Wohler’s classical synthesis of urea from ammonium cyanate may be carried
out by evaporating solutions of sodium cyanate and ammonium sulphate
In aqueous solution at 100° the change is reversible and equilibrium is reached when 95 per cent, of the ammonium cyanate has changed into urea. Urea is less soluble in water than is ammonium sulphate, hence if the solution is evaporated, urea commences to separate, the equilibrium is disturbed, more ammonium cyanate is converted into urea to maintain the equilibrium and eventually the change into urea becomes almost complete. The urea is isolated from the residue by extraction with boiling methyl or ethyl alcohol. The mechanism of the reaction which is generally accepted involves the dissociation of the ammonium cyanate into ammonia and cyanic acid, and the addition of ammonia to the latter
The industrial methods of preparation are :—
by partial hydrolysis of cyanamide, itself derived from calcium cyanamide