Beyond the reaction pathways of ortho-phenylene diamine and thiosemicarbazide

Reports have shown that solvent free reaction between ortho-phenylene diamine and thiosemicarbazide could lead to the production of a heterocyclic compound, which is an important product in pharmaceutics. In this project, the theoretical approaches that contain the reaction pathways and the mechanism to study them have been used in order to find both the mechanism and possible products that might emerge. In the course of examining the mechanism of that reaction, a scheme, containing eight minor pathways were devised and fifteen different transition states were found as well. Regardless of the mechanism, the relative potential energy surface showed that in each path, the substitution process on the carbon center of the aromatic ring appeared to be much more difficult than substitution on the thioamide carbon center (thiosemicarbazide). The results showed that the phenylene diamine and thiosemicarbazide reaction would produce benzimidazole-2-thione.