Isothiazole chemistry. IV. Cyanide cleavage of the S-N bond in 3-hydroxyisothiazole

Abstract

Nucleophilic attack on 3-hydroxyisothiazole by cyanide ion, yielding cis-3-thiocyanoacrylamide, has been investigated over the pH range 0.00-5.50. Rate constants have been measured both for direct attack by cyanide ion and from the effect of cyanide ion in retarding the cyclization of the thiocyanoacrylamide; in both cases the derived rate constants agree. The pH-rate profile of the reaction reveals the existence of two kinetically discrete mechanisms. Within the range 5.50-4.00 the dominating mechanism is one involving a slow direct attack on 3-hydroxyisothiazole itself, while at pH less than 3.50 the conjugate acid of this molecule is subjected to a much faster attack. Equilibrium studies have been made for the system, and the effect of temperature on the equilibrium constant has been used to derive thermodynamic parameters.