A study of the behaviour of some substituted 1,2,4-triazoline-3-thiones in different media

The acid-base behaviour of 4-phenyl-5-(4-R-benzyl)-1,2,4-triazoline-3-thione (1(R = OH); 2(R = OC2H5)) was studied in aqueous sulfuric acid and sodium hydroxide solutions. Three ionisation equilibria of compound 1 (pKBH3+ = 4.64, pKBH2 = 7.50, pKBH = 10.06) and two ionisation equilibria of compound 2 (pKBH2+ = 4.82, pKBH = 7.45) were found. The first equilibrium belongs to the protonation of 1,2,4-triazoline-3-thione, while the second belongs to the dissociation of the same part of the molecule. The third equilibrium represents the dissociation process of the phenolic OH group of compound 1. The kinetics of hydrolysis of compounds 1 and 2 were studied in high concentrated sulfuric acid solutions. The hydrolysis follows an irreversible first-order consecutive reaction path.