Calculation of the Standard Potentials of the Dithiocarbamate/thiuram Disulfide Redox System via Thermochemical Cycles and Computational Electrochemistry

Ab initio and density functional levels of electronic structure theory are applied to calculate the standard potentials of alternative routes for the oxidation of dithiocarbamic anions and the reductive cleavage of thiuram disulfide. The reactions are modeled with dithiocarbamic acid H₂NCS₂H and thiuram disulfide (H₂NCS₂)₂. Aqueous and DMSO solvation effects are included using IPCM and PCM continuum solvation models. A pathway proceeding via a single electron detachment followed by radical dimerization is predicted to be the most favorable mechanism for dithiocarbamic anion (or acid) oxidation. Two pathways of the reduction of thiuram disulfides are tested. In the gas phase the reaction is more likely (energetically preferred) to proceed in a stepwise manner, that is, the electron attachment is followed by the S--S bond splitting. In the solvent environments the concerted bond breaking electron transfer mechanism is predicted to potentially be equally probable.