Hydrolysis of isothiocyanic acid in strongly acid solutions

Abstract

Alkali-metal thiocyanates are hydrated in strongly acid solutions to an intermediate that breaks down slowly to ammonium ion and carbonyl sulphide. Different intermediates are formed at high and low mineral acid concentrations; the low-acidity species is suggested to be protonated thiocarbamic acid. The rate of disappearance of thiocyanate follows the rate law v=k[HNCS]h₀a_H2O, and is a maximum in 70% sulphuric acid. Kinetic, spectrophotometric, and partition measurements suggest that isothiocyanic acid acts as a base and is fully protonated in 85% sulphuric acid.