Thiocyanic acid

Thiocyanic acid is a chemical compound with the formula HSCN which exists as a tautomer with isothiocyanic acid (HNCS).[4] The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase.[5]

Tautomerism between thiocyanic acid (left) and isothiocyanic acid (right)
Thiocyanic acid[1]
Skeletal formula of thiocyanic acid
Skeletal formula of thiocyanic acid with the explicit hydrogen added
Names
IUPAC name
Nitridosulfanidocarbon[2]
Other names
  • Hydrogen thiocyanate
  • Sulfocyanic acid[3]
  • Sulfocyanide
Identifiers
3D model (JSmol)
3DMet
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.006.672
EC Number
  • 207-337-4
25178
KEGG
MeSH thiocyanic+acid
UNII
Properties
CHNS
Molar mass 59.09 g·mol−1
Appearance colorless, oily liquid
Odor pungent
Density 2.04 g/cm3
Melting point 5 °C (41 °F; 278 K)
Miscible
Solubility soluble in ethanol, diethyl ether
log P 0.429
Acidity (pKa) 0.926
Basicity (pKb) 13.071
Hazards
Xn
R-phrases (outdated) R20/21/22, R32, R52/53
S-phrases (outdated) (S2), S13
Related compounds
Related alkanenitriles
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

It is a weak acid, bordering on strong, with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength.[6]

HSCN is predicted to have a triple bond between carbon and nitrogen. It has been observed spectroscopically but has not been isolated as a pure substance.[7]

The salts and esters of thiocyanic acid are known as thiocyanates. The salts are composed of the thiocyanate ion (−SCN) and a suitable metal cation (e.g., potassium thiocyanate, KSCN). The esters of thiocyanic acid have the general structure R–SCN.

Isothiocyanic acid, HNCS, is a Lewis acid whose free energy, enthalpy and entropy changes for its 1:1 association with a variety of Lewis bases in carbon tetrachloride solution at 25°C have been reported.[8] HNCS acceptor properties are discussed in the ECW model.

References
  1. Merck Index, 11th Edition, 9257.
  2. "thiocyanic acid (CHEBI:29200)". Chemical Entities of Biological Interest. USA: European Bioinformatics Institute. 18 October 2009. Main. Retrieved 5 June 2012.
  3. Richter, Victor von; Spielmann, Percy E., trans. (1922). Organic Chemistry or Chemistry of the Carbon Compounds. vol. 1. Philadelphia, Pennsylvania, U.S.A.: P. Blakiston's Son & Co. p. 466.
  4. Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
  5. Beard, C. I.; Dailey, B. P. (1950). "The Structure and Dipole Moment of Isothiocyanic Acid" (PDF). The Journal of Chemical Physics. 18 (11): 1437. Bibcode:1950JChPh..18.1437B. doi:10.1063/1.1747507. hdl:1721.1/4934.
  6. Martell, A. E.; Smith, R. M.; Motelaitis, R. J. (2001). NIST Database 46. Gaithersburg, MD: National Institute of Standards and Technology.
  7. Wierzejewska, M.; Mielke, Z. (2001). "Photolysis of Isothiocyanic Acid HNCS in Low-Temperature Matrices. Infrared Detection of HSCN and HSNC Isomers". Chemical Physics Letters. 349 (3–4): 227–234. Bibcode:2001CPL...349..227W. doi:10.1016/S0009-2614(01)01180-0.
  8. . Barakat, T. M.; Nelson, J.; Nelson, S. M.; Pullin, A. D. E. (1969.) “Spectra and hydrogen-bonding of characteristics of thiocyanic acid. Part 4.—Association with weak proton acceptors”. Trans. Faraday Soc., 1969,65, 41-51
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