Ammonium thiocyanate is an inorganic compound with the formula NH 4 SCN. It is a salt of ammonium cation and thiocyanates anion .
Ammonium thiocyanate is used in the manufacture of herbicides, thiourea and transparent synthetic resins; in matches ; As a stabilizing agent in photography; in various anti-corrosion compositions; As an assistant in textile dyeing and printing; As a tracer in oil fields; In the separation of hafnium from zirconium, and in titer analysis.
In May 1945, USAAF General Victor E. Betrandius proposed to his superior General Arnold the use of ammonium thiocyanate to deplete rice crops in Japan, as part of a bombing raid on his country. Ammonium thiocyanates can also be used to determine the iron content in soft drinks by colorimetry.
Ammonium thiocyanate can also be used to separate quinine from alcohol, after separating quinine from neutral, aqueous, sulfate solutions. The salt is added to the hot solution and the viscous solid that forms separates from the liquid. The solid is then refluxed with methanol, which dissolves most of the impurities, leaving quinidine thiocyanate as a crystalline solid of 90–95% purity. After separation, (usually by centrifugation) the solid can then be purified for drug quality. (Quinidine is used for the treatment of heart arrhythmias and is therefore of great importance.)
Ammonium thiocyanate is formed by the reaction of carbon disulfide with aqueous ammonia. In this reaction ammonium dithiocarbamate is formed as an intermediate, which on heating decomposes into ammonium thiocyanate and hydrogen sulfide:
CS 2 + 2 NH 3 (aq) → NH 2 CH (= S) SNH 4 → NH 4 Scn + H 2 s
Ammonium thiocyanate is stable in air; However, on heating it isomerizes to thiourea:
The equilibrium mixtures at 150 °C and 180 °C contained 30.3% and 25.3% (by weight) thiourea, respectively. When heated to 200 °C, the dry powder decomposes into ammonia, hydrogen sulfide and carbon disulfide, leaving a residue of guanidinium thiocyanate.
NH 4 SCN is weakly acidic due to the ammonium ion ; It reacts with alkali hydroxides such as sodium hydroxide or potassium hydroxide to form sodium thiocyanate or potassium thiocyanate with water and ammonia. The thiocyanate ion, in particular, reacts with ferric salts to form a dark red ferric thiocyanate complex:6scn – + Fe 3+ → [Fe (scn) 6 ] 3−
Ammonium thiocyanate reacts with many metal ions, including copper, silver, zinc, lead and mercury, to form their thiocyanate precipitates, which can be extracted in organic solvents.