Ammonium thiocyanate

Ammonium thiocyanate
Identifiers
CAS number	1762-95-4 Y
PubChem	6857883
ChemSpider	14901 Y
RTECS number	XN6465000
Jmol-3D images	Image 1
SMILES [S-]C#N.[NH4+]
InChI InChI=1S/CHNS.H3N/c2-1-3;/h3H;1H3 Y Key: SOIFLUNRINLCBN-UHFFFAOYSA-N Y InChI=1/CHNS.H3N/c2-1-3;/h3H;1H3 Key: SOIFLUNRINLCBN-UHFFFAOYAF
Properties
Molecular formula	NH4SCN
Molar mass	76.122 g/mol
Appearance	Colorless hygroscopic crystalline solid
Density	1.305 g/cm3
Melting point	149.5 °C, 423 K, 301 °F
Boiling point	170 °C (decomp)
Solubility in water	128 g/100 mL (0 °C)
Solubility	soluble in liquid ammonia, alcohol, acetone
Hazards
MSDS	External MSDS
NFPA 704	1 2 1
Y thiocyanate (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

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 guanidine 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.