Tautomeric Equilibrium Modeling: Stability and Reactivity of Benzothiazole and Derivatives

Benzothiazoles are organic compounds with multiple biological activities. Due to their biological interests, these are synthesized on a large scale at the industrial level and used in various fields. Their release into waters causes environmental problems which leads to public health problems. Finding solution which can help for their degradation become necessary. That is the reason why a theoretical study of the reactivity of five benzothiazole derivatives has been initiated in order to understand some aspect of their biodegradation. The calculations were carried out in gaseous and aqueous phase with B3LYP functional associated with bases 6-311G(d) and 6-31+G(d). The results revealed that the thione tautomer of the MBT derivative is more stable than the thiol form. These results are in agreement with previous experimental work which showed that the thiones forms in MBT metal complexes are the most stable. Moreover, the study of the reactivity based on the computation of the global indices of reactivity reveals that the benzothiazoles BT, OBT and MBT are the most reactive. The most electrophilic is BT and the least electrophilic is MTBT. In addition, the thermodynamic parameters and the energy barriers predict a possibility of coexistence of tautomers ol and one of OBT derivative. Fukui dual descriptors have shown that the carbon C2 of BT is the most electrophilic. In substituted derivatives, it is the C6 carbon that is the most electrophilic. N3 nitrogen remains the most nucleophilic site in all the studied molecules.