Electrophilic nitrosation at sulphur and nitrogen in thiourea

Abstract

Thiourea reacts rapidly with nitrous acid in aqueous solution to form an equilibrium concentration of a coloured S-nitroso-compound. The equilibrium constant has been measured, together with a preliminary value of the rate constant for the nitrosation. The kinetics of the much slower reaction to form nitrogen and thiocyanic acid have been investigated. The mechanism proposed is a rate-determining sulphur-to-nitrogen migration of the nitroso-group in the conjugate base of the S-nitroso-compound.