Alternative pathway to brominate 2,13-benzothiadiazole: Preparation of 4,7-dibromobenzo[c]-1,2,5-thiadiazole via N-bromosuccinimide

Abstract

This present work reports an alternative pathway to brominate the 2,1,3-benzothiadiazole (BT). The conventional method to brominate a phenyl/benzene ring is to use the bromine solution (Br2) together with hydrobromic acid (HBr). This is because the phenyl/benzene rings exhibit high stability due to the delocalized -conjugation, which the substitution of bromines into the rings can only be done through a strong bromination source, e.g. the Br2/HBr. Besides that, there is another bromine source, known as N-bromosuccinimide (NBS), which is normally used for bromination of thiophene rings but not the phenyl/benzene ring. The bromination ability of NBS is relatively mild than the Br2/HBr. Herein, this research shows that bromination of benzene/phenyl ring through NBS is possible under a drastic condition that involved the usage of 96% concentrated sulphuric acid and chloroform at room temperature. This alternative pathway can be used when there is limit access to the Br2 and bromination through NBS is relatively less dangerous than the Br2/HBr.