Theoretical Assessment of Inhibitive Behavior of Some Long Chain Fatty Acid Oxadiazoles

Some long chain fatty acid oxadiazoles are good corrosion inhibitors in the presence of acidic environment for mild steel and N80 steel surfaces. In this study, 2-undecane-5-mercapto-1-oxa-3,4-diazole-2-thiol(thione) (UMOD), 2-heptadecene-5-mercapto-1-oxa-3,4-diazole-2-thiol(thione) (HMOD) and 2-decene-5-mercapto-1-oxa-3,4-diazole-2-thiol(thione) (DMOD) as neutral and protonated forms in gas and aqueous phases have been studied using density functional theory (DFT) with the B3LYP/6-311G level calculations. In addition, the inhibitive effect of studied inhibitors against the corrosion of neutral iron surface is studied in aqueous phases by means of same calculation method. The calculations were made for both molecule structures, since the molecules examined show thione-thiol tautomerism. Optimized molecular structure, highest occupied molecular energy level (E_HOMO), lowest unoccupied molecular energy level (E_LUMO), the energy gap between E_LUMO and E_HOMO (∆E_LUMO–HOMO), electronegativity (χ), hardness (η), softness (σ), dipole moment (μ), the fraction of electrons transferred from the inhibitor to metal surface, surface (ΔN) were correlated to corrosion inhibition efficiency of studied compounds and the results were interpreted. Molecular electrostatic potential (MEP) distributions of some long chain fatty acid oxadiazoles have been studied.