Computational Studies for Inhibitory Action of 2-Mercapto-1-Methylimidazole Tautomers on Steel Using of Density Functional Theory Method (DFT)

The inhibition activity of thione–thiol tautomers of 2-mercapto-1-methylimidazole (MMI), namely 1-methyl-1Himidazole-2 (3H)-thione (M1) and 1-methyl-1H-imidazole-2-thiol (M2) has been performed using density functional theory (DFT) B3LYP/6-311G (d, P) basis set level in order to elucidate the different inhibition efficiencies of these compounds as corrosion inhibitors. The calculated structural parameters correlated to the inhibition efficiency are the frontier molecular orbital energies EHOMO (Highest occupied molecular orbital energy), ELUMO (Lowest unoccupied molecular orbital energy), energy gap (∆E), dipole moment (μ), hardness (η), softness (S), the absolute electronegativity (χ), the electrophilicity index (ω) and the fractions of electrons transferred (∆N) from thione–thiol tautomer molecules to iron. The highest value of EHOMO is 5.30241 (eV) of M1 indicates the better inhibition efficiency than the other inhibitor M2. In our study, the trend for the (∆Eg gap) values follows the order M1>M2, which suggests that inhibitor M1 has the highest reactivity in comparison to M2 and would therefore likely interact strongly with the metal surface. The parameters like hardness (η), Softness (S), dipole moment (μ), electron affinity (EA) ionization potential (IE), electronegativity (χ) and the fraction of electron transferred (∆N) confirms the inhibition efficiency in the order of M1>M2.