Potent 1,2,4-Triazole-3-thione Radical Scavengers Derived from Phenolic Acids: Synthesis, Electrochemistry, and Theoretical Study

Nine 1,2,4-triazole-3-thiones containing phenolic acid moiety have been synthesized and examined by scavenging of stable DPPH (2,2-diphenyl-1-picrylhydrazyl) radical, measurement of reducing capacity, cyclic voltammetry experiments and density functional theory (DFT). The differences in DPPH-radical scavenging activity of the compounds 4a-i are affected by the stability of the corresponding radicals or radical cations and possibility of delocalization of unpaired electron through benzene and triazole ring. Significantly, lower proton affinity (PA) values than bond dissociation enthalpy (BDE) indicate SPLET (sequential proton loss electron transfer) mechanism under these experimental conditions.