Ammonium thiocyanate

Ammonium thiocyanate
Identifiers
1762-95-4 N
ChEBI CHEBI:30465 YesY
ChemSpider 14901 N
Jmol interactive 3D Image
PubChem 15666
RTECS number XN6465000
Properties
NH4SCN
Molar mass 76.122 g/mol
Appearance Colorless hygroscopic crystalline solid
Density 1.305 g/cm3
Melting point 149.5 °C (301.1 °F; 422.6 K)
Boiling point 170 °C (338 °F; 443 K) (decomposes)
128 g/100 mL (0 °C)
Solubility soluble in liquid ammonia, alcohol, acetone
Hazards
Safety data sheet External MSDS
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
1
2
1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Ammonium thiocyanate is an inorganic compound with the formula NH4SCN. It is the salt of the ammonium cation and the thiocyanate anion.

Uses

Ammonium thiocyanate is used in the manufacture of herbicides, thiourea, and transparent artificial resins; in matches; as a stabilizing agent in photography; in various rustproofing compositions; as an adjuvant in textile dyeing and printing; as a tracer in oil fields; in the separation of hafnium from zirconium, and in titrimetric analyses.

Ammonium thiocyanate can also be used to determine the iron content in soft drinks by colorimetry.

Preparation

Ammonium thiocyanate is made in the United States by the reaction of carbon disulfide with aqueous ammonia. Ammonium dithiocarbamate is formed as an intermediate in this reaction, which upon heating, decomposes to ammonium thiocyanate and hydrogen sulfide:

CS2 + 2 NH3(aq) → NH2C(=S)SNH4 → NH4SCN + H2S

Reactions

Ammonium thiocyanate is stable in air; however, upon heating it isomerizes to thiourea:

The equilibrium mixtures at 150 °C and 180 °C contain 30.3% and 25.3% (by weight) thiourea, respectively. When heated at 200 °C, the dry powder decomposes to ammonia, hydrogen sulfide, and carbon disulfide, leaving a residue of guanidinium thiocyanate.

NH4SCN is weakly acidic; reacts with caustic soda or caustic potash to form sodium thiocyanate or potassium thiocyanate. It reacts with ferric salts to form a deep-red ferric thiocyanate complex:

6 SCN− + Fe3+ → [Fe(SCN)6]3−

Ammonium thiocyanate reacts with several metal ions including copper, silver, zinc, lead, and mercury, forming their thiocyanate precipitates, which may be extracted into organic solvents.

References

    1. A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984. ISBN 978-0198553700
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