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

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 (Br 2 ) 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 Br 2 /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 Br 2 /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 Br 2 and bromination through NBS is relatively less dangerous than the Br 2 /HBr.