Nucleophilic substitution at bivalent sulphur. Part V. A study of exchange reactions at bivalent sulphur using 19F nuclear magnetic resonance spectroscopy

Abstract

Exchange broadening is observed in the ¹⁹F n.m.r. spectrum of a solution of bis-(2-nitro-4-trifluoromethylphenyl) disulphide and the corresponding thiolate ion. The rate of exchange is dependent on concentration and solvent composition. A rate constant of 1·5 × 10⁴ l mol^–1 s^–1 is calculated for exchange at 70°. A rapid exchange leading to line broadening is also obtained with an equimolar mixture of potassium cyanide and 2-nitro-4-trifluoromethylphenyl thiocyanate. These compounds react to give the thiolate ion which then gives the monosulphide by reaction with starting material. No exchange was observed with 2-nitro-4-trifluoromethylbenzenesulphenanilide and aniline, no with the corresponding sulphenyl thiocyanate and potassium thiocyanate, although potassium cyanide reacted with this compound to give the aryl thiocyanate. No evidence was obtained for the formation of an intermediate during substitution at sulphur.