Theoretical Studies on the Efficiencies of Some Triazolopyrimidine Derivatives as Corrosion Inhibitors of Mild Steel in Acidic Medium Using AM1 and DFT Approach

A quantum chemical study of the efficiency of some Triazolopyrimidine derivatives as corrosion inhibitors of mild steel in H2SO4 was investigated. The AM1 semi-empirical method and Density Functional Theory (DFT) at the B3LYP/6-31G* level were used. The calculated quantum chemical parameters related to the inhibition efficiencies are the orbital energies (EHOMO and ELUMO), Separation Energy (ELUMO-EHOMO), Dipole moment (μ), Log P, Polarizability, Hardness (η) and Softness (S). A good correlation between the quantum chemical parameters and the experimental inhibition efficiency was observed. Quantitative Structure Activity Relationship (QSAR) approach was used on a composite index of some quantum chemical parameters to characterize the inhibition performance of the studied molecules. The results showed that the Inhibition Efficiency was closely related to some of the quantum chemical parameters. The calculated (theoretical) Inhibition Efficiency of the molecules was found to be close to their experimental Inhibition Efficiency. Results revealed that mol 2 (Pyrimidine thione) showed greater Inhibition Efficiency (IE) than the Pyrimidinones.