Formation of trithiocyanate in the oxidation of aqueous thiocyanate

Oxidation of SCN- in acidic media by a deficiency of aqueous chlorine generates a transient UV absorption feature in less than 3 ms. This intermediate has the same spectral and kinetic features as were found in prior studies of the oxidation of SCN- by H2O2 or ClO2. The UV absorbance increases strongly with increasing concentration of SCN- but not with increasing [H+]. These observations are evidence that (SCN)2 and (SCN)3- both contribute to the absorbance and are in equilibrium with each other. Values of the corresponding molar absorptivities and the equilibrium constant are derived. Hydrolysis of (SCN)2 to HOSCN is shown to have a small equilibrium constant.