|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||59.09 g·mol−1|
|Appearance||colorless, oily liquid|
|Melting point||5 °C (41 °F; 278 K)|
|Solubility||soluble in ethanol, diethyl ether|
|H302, H312, H332, H412|
|P261, P264, P270, P271, P273, P280, P301+P312, P302+P352, P304+P312, P304+P340, P312, P322, P330, P363, P501|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Thiocyanic acid is a chemical compound with the formula HSCN and structure H−S−C≡N, which exists as a tautomer with isothiocyanic acid (H−N=C=S). The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase.
It is a moderately strong acid, with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength.
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.
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. HNCS acceptor properties are discussed in the ECW model.