NH4SCN
Ammonium thiocyanat

Chemical properties

Ammonium thiocyanate forms colourless, monoclinic crystals which appear white in the crystalline powder. They are highly soluble in water and ethyl alcohol. The substance is strongly hygroscopic, the crystals dissolve in air. When heated to 70 to 120 °C thiourea is formed. When heated strongly to over 170 °C, decomposition takes place and hydrogen cyanide, ammonia and nitrogen oxides are formed. Mixing with barium hydroxide produces an efficient cooling mixture. In an endothermic reaction the mixture cools down to -26.7 °C.

Production

Ammonium thiocyanate can be produced from carbon disulphide and ammonia under pressure and elevated temperature:

CS2 + 2 NH3 → NH4SCN + H2S

Use

It is used as a stabilizer for photographic developers, as a vulcanization accelerator, as an accelerator for mortar and concrete and in herbicides.

From ammonium thiocyanate and barium hydroxide it is possible to produce a refrigeration mixture that generates particularly low temperatures.

In analytical chemistry it serves as a detection reagent for iron(III) ions. The very intense red colour in aqueous solution is due to the presence of undissociated [Fe(SCN)3(H2O)3] in addition to the ions [Fe(SCN)2(H2O)4]+ and [Fe(SCN)(H2O)5]2+.

Security

Ammonium thiocyanate has been included by the EU in 2013 in the Community rolling action plan (CoRAP) under Regulation (EC) No 1907/2006 (REACH) as part of the substance evaluation. This involves reassessing the effects of the substance on human health and the environment and, if necessary, taking follow-up action. The inclusion of ammonium thiocyanate was motivated by concerns about high (aggregated) tonnage, high risk characterisation ratio (RCR) and widespread use, as well as the risks associated with its possible classification as a CMR substance and as a potential endocrine disruptor. The reassessment was carried out from 2015 and was performed by the Czech Republic. A final report was then published. There was no need for EU-wide regulatory measures.