Quantum Chemical Studies on the Corrosion Inhibition of Mild Steel by Some Triazoles and Benzimidazole Derivatives in Acidic Medium

Quantum chemical calculations using the Density Functional Theory (DFT) method at three different basis sets, namely, 6-31(d,p), 6-31+(d,p) and 6-311G(d,p) were performed on selected triazole and benzimidazole derivatives, namely 2-aminobenzimidazole (ABI), 1,3-benzothiazole (BTH), benzotriazole (BTA), 2-methylbenzimidazole (MBI), 2-(2-pyridyl)benzimidazole (PBI), 2-(amino methyl) benzimidazole (AMBI), 5-amino-3-mercapto-1,2,4-triazole (5AMTZ), 2-hydroxybenzimidazole (HBI), benzimidazole (BI) and 5-amino-1,2,4-triazole (5ATZ), to determine their reactive centres which might interact with the metal surface on the adsorption of the these compounds onto the metal surface. The results show that the adsorption of the inhibitor onto the metal surface would preferentially be through the benzene ring that is fused to the heterocyclic ring and through the heteroatoms of the heterocyclic ring. The study on the protonated species of the studied compounds show that they have the least tendency to chemically adsorb onto the metal surface and might preferentially adsorb physically. The quantitative structure activity relationship approach indicates that three to four quantum chemical parameters are needed to effect a reasonable correlation between experimentally determined and theroetically estimated inhibition efficiencies.