Thiocyanic acid is a chemical compound with the formula and structure, which exists as a tautomer with isothiocyanic acid .[1] The isothiocyanic acid tautomer tends to dominate with the compound being about 95% isothiocyanic acid in the vapor phase.[2]
It is a moderately strong acid,[3] with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength.[4]
One of the thiocyanic acid tautomers, HSCN, is predicted to have a triple bond between carbon and nitrogen. Thiocyanic acid has been observed spectroscopically.[5]
The salts and esters of thiocyanic acid are known as thiocyanates. The salts are composed of the thiocyanate ion and a suitable cation (e.g., potassium thiocyanate, KSCN). The esters of thiocyanic acid have the general structure, where R stands for an organyl group.
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.[6] < HNCS acceptor properties are discussed in the ECW model. The salts are composed of the thiocyanate ion and a suitable cation (e.g., ammonium thiocyanate,). Isothiocyanic acid forms isothiocyanates, where R stands for an organyl group.
Thiocyanuric acid is a stable trimer of thiocyanic acid.