A Theoretical Study of Structure and Corrosion Inhibition of Some Heterocyclic Imidazoles: DFT Investigation

Abstract

The polarizable continuum model was used for four different compounds to investigate the impact of substituent groups, of the number of π-electrons, of the electron-accepting and electron-donating properties on the corrosion inhibiting properties in both aqueous and gas phases for the neutral and cationic forms of the studied subsdtances. Measures for the corrosion prevention of metals are of great importance in the industrial, environmental (or ecologic), aesthetic, and economic fields. The use of inhibitors is the best way to preserve metals and alloys from corrosion. The purpose of this study was to apply quantum chemical calculations in the research of the corrosion inhibition and adsorption properties of four compounds with various heteroatoms or substituent groups but with similar chemical skeleton structures: 2-mercaptoimidazole, 2-mercapto-5-methyl benzimidazole, 2-mercaptobenzoimidazole, and 2-mercapto-5-nitrobenzimidazole, shown in Figs. 1 and 2 and designated as A, C, B, and D, respectively. The quantum chemical computations sector of the study gives complete calculation details and discussion on the correlation between corrosion inhibition and global reactivity descriptors such as the energy of the highest occupied molecule orbital, the energy of the lowest unoccupied molecule orbital, total energy, ionization energy, electron affinity, electronegativity, energy gap, hardness, softness, dipole moment, electron transfer, chemical potential, electrophilicity, nucleophilicity, and back-donation energy. The calculations were carried out using the general purpose computational chemistry software package Gaussian 09. The total calculations have been done based on the density functional theory at 6-311++G(d, p) basis set and applying the hybrid functional B3LYP level taking into account the exchange and the correlation with three parameters defining the hybrid Becke’s functional (Becke—the exchange part, and Lee, Yang and Parr—the correlation part). Based on the calculations performed in this paper, the following summary ranking was obtained for the corrosion inhibition efficiency: A > B > C ≈ D for neutral forms and A > B > C > D for cationic forms in the gas phase, A > C ≈ D > B for neutral forms and A ≈ B > C > D for cationic forms in the aqueous phase. Thus, inhibitor A should be considered to be the best one in all cases.