In this study, seven new 3-alkyl(aryl)-4-[3,4-di-(4-nitrobenzoxy)-benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones (4) were synthesized by the reactions of 3-alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (2) with 3,4-di-(4-nitrobenzoxy)-benzaldehyde (3) which had also been synthesized by the reactions of 3,4-dihydroxybenzaldehyde with 4-nitrobenzoyl chloride by using triethylamine. The acetylation reactions of compounds 4 were investigated and six new 5 type compounds were obtained. The new thirteen compounds were characterized by elemental analyses and IR, 1H NMR, 13C NMR, UV and mass spectral data. In addition, the synthesized compounds were analysed for their in vitro potential antioxidant activities in three different methods. Compound 4g showed the best activity for antioxidant results. Moreover, the compounds 4 were titrated potentiometrically with tetrabutylammonium hydroxide (TBAH) in four non-aqueous solvents. Thus, the half-neutralization potential values and the corresponding pKa values were determined in all cases.