Transition state structures of elementary reactions of benzimidazole synthesis in the presence of graphene quantum dot: a DFT study

Benzimidazole is the central core for drug synthesis. Obtaining detailed information about its synthesis mechanism can help us to design new catalysts to increase synthesis yield. Our previous results showed that in the absence of any catalysts, the steps ۱ and ۳ in which nitrogen in phenylene diamine attack on the formic acid carbon have higher barrier energies; while, dehydration steps (steps ۲ and ۴) have less barrier energies. In this paper, graphene quantum dot is used as a catalyst for benzimidazole synthesis, and all elementary steps are in detail studied. Stabilization energy due to the interaction between two reactants (formic acid and phenylene diamine) in the absence and presence of graphene catalyst are -۹.۰۸ and -۲۶.۲۹ kcal·mol-۱, respectively. This causes that the rate determining step (RDS) is reduced more when graphene is used as the catalyst. The RDS for benzimidazole synthesis in the absence and presence of catalyst are ۳۶.۰۵ and ۲۷.۸۸ kcal·mol-۱, respectively. In addition to the RDS, all other transition structures in the presence of graphene have energies less than the total energies of isolated formic acid and phenylene diamine. Considering thermal, entropic, and solvation free energy corrections reduces the relative barrier energy by ۲.۱۸ kcal·mol⁻¹. These corrections include zero-point vibrational energy (ZPVE), thermal contributions (TS and H), and solvation free energy (ΔGsolv), which together provide a more accurate representation of the reaction energetics.

کلیدواژه ها:

benzimidazole synthesis ، Reaction mechanism ، LST/QST ، Transition State ، graphene catalyst