Computational Studies on the Corrosion Inhibition of Mild Steel Using Pyrimidine Derivatives

Quantum chemical parameters and molecular dynamic simulation studies were used to evaluate the corrosion inhibition of mild steel using pyrimidine derivatives (5-Phenoxy-6-phenyl-4-p-tolyl-1H pyrimidin-2-one (PMO), 5-(7-Oxa-bicyclo[4.1.0]hepta-1(6),2,4-trien 2-yloxy)-pyrimidine-2,4-diamine (PMA), and 5-Phenoxy-6-phenyl-4- p-tolyl-1H-pyrimidine-2-thione (PMS)) as inhibitors. The pyrimidine derivatives were geometrically optimized using DFT with a restricted spin polarization, DNP basis set, and a local density function B3LYP. According to the local or global reactivity parameters investigated, including the energy gap (ΔE), dipole moment (μ), electronegativity (χ), global hardness (η), global electrophilicity index (ω), nucleophilicity (ε), energy of back donation (ΔEb-d), and fraction of electron transfer (ΔN) between the inhibitor molecule and the iron surface, PMS is relatively a better inhibitor on Fe(111) surface than other inhibitors studied. This is demonstrated by its higher nucleophilicity. According to the evaluated Fukui indices, the interaction point between molecules and Fe(111) surface involve heteroatoms of sulphur, oxygen, and nitrogen that donate electrons which are wholly nucleophilic in nature. The nature and strength of the compounds adsorption on the Fe(111) surface was described by quenched molecular dynamics simulations in the following order: PMS PMO PMA. There is relatively a weak interaction for the studied molecules with the Fe(111) surface, according to the measured molecular bond lengths and angles before and after adsorption and as well as the calculated adsorption/binding energies. It is suggested that physical adsorption mechanism can be used to describe the nature of the interaction of the pyrimidine derivative molecules with the Fe (111) surface.