A comprehensive electrochemical study of 2-mercaptobenzoheterocyclic derivatives. Air-assisted electrochemical synthesis of new sulfonamide derivatives

Abstract

In this work, we have introduced a green air-assisted electrochemical method for the synthesis of new sulfonamide derivatives via oxidative coupling of heterocyclic thiols and amines. The synthetic method was designed based on the data collected from electrochemical oxidation of heterocyclic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI) in the absence and presence of amines. The electrochemical results indicate that the oxidation of MBO and MBT lead to the formation of the corresponding dimers, which as an intermediate is essential for sulfonamide synthesis. The results also show that, in the time scale of our voltammetric experiments, oxidation of MBI does not lead to dimer formation. Our voltammetric studies suggest that the formed dimer is adsorbed on the electrode surface. The amount and intensity of adsorption depends on the type heterocyclic thiol, solvent, switching potential and solution pH. The mechanism of synthesis of sulfonamide compounds has been established based on the disappearing of the dimer reduction peak in the cyclic voltammogram of MBO in the presence of amines along with increasing the number of electrons transferred in this condition, as well as spectroscopic data of the products. These compounds have been successfully synthesized in water/ethanol mixture solutions in an undivided cell, at carbon rod electrodes, by constant current electrolysis at room temperature. The proposed method does not need to use toxic solvent, metal, catalyst and challenging workups. This method is easy to scale-up and the products have antibacterial activity.