New Thiosemicarbazides and 1,2,4-Triazolethiones Derived from 2-(Ethylsulfanyl) Benzohydrazide as Potent Antioxidants

New thiosemicarbazide derivatives 2–6 were synthesised by reacting 2-(ethylsulfanyl)benzohydrazide with various aryl isothiocyanates. The cyclisation of compounds 2–6 under reflux conditions in a basic medium (aqueous NaOH, 4 N) yielded compounds 7–11 that contain a 1,2,4-triazole ring. All of the synthesised compounds were screened for their antioxidant activities. Compounds 2, 3, and 7 showed better radical scavenging in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, with IC(50) values of 1.08, 0.22, and 0.74 µg/mL, respectively, compared to gallic acid (IC(50), 1.2 µg/mL). Compound 3 also showed superior results in a ferric reducing antioxidant power (FRAP) assay (3054 µM/100 g) compared to those of ascorbic acid (1207 µM/100 g).