Thiocyanic acid

Thiocyanic acid is a chemical compound with the formula HSCN which exists as a tautomer with isothiocyanic acid (HNCS). The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase. Thiocyanic acid is a chemical compound with the formula HSCN which exists as a tautomer with isothiocyanic acid (HNCS). The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase. It is a weak acid, bordering on strong, 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.