Thermal dissociation of thiuram disulfides in solution; an electron spin resonance and kinetic study

Abstract

Tetraisopropylthiuram disulfide dissociates reversibly in solution to form dithiocarbamate thioradicals which can be detected by e.s.r. (g 2.015). The thermodynamics of the dissociation has been examined in decalin by quantitative e.s.r. and a dissociation enthalpy of 104 � 2 kJ mol-1 and anentropy of dissociation of 57 � 5 JK-1 mol-1 has been obtained. Replacing the isopropyl group by other alkyl groups significantly affects the extent of dissociation which decreases in the sequence isopropyl ≈ cyclohexyl > ethyl ≈ methyl > benzyl as the alkyl group is changed. Studies of the kinetics of dissociation of the thiuram disulfides are consistent with the e.s.r, observations and indicate that thio radical recombination occurs at a near diffusion-controlled rate.