Ab initio study of unimolecular pyrolysis mechanisms of dithioformic acid Original Research Article

The mechanisms of the two possible unimolecular competing reactions occurring during the pyrolysis of dithioformic acid have been proposed and investigated by ab initio calculations with a variety of basis sets. The effects of valence electron correlation were included by Møller-Plesset (MP) perturbation theory to the fourth order at the 6-31G∗∗ level. The activation energies given by our best results (MP4/6–31G∗∗//HF/6–31G∗∗ level plus scaled zero-point energy) are 63.68 kcal/mol for pathway A (dehydrogensulfidation) and 72.73 kcal/mol for pathway B (dehydrogenation). The reaction heats of these two reactions are 29.89 and −10.12 kcal/mol respectively. These results demonstrate that the dehydrogensulfidation of s-cis dithioformic acid is more favorable than the dehydrogenation of its s-trans conformer.