Abstract

Corrosion Inhibitors Part IV: Quantum Chemical Studies On The Corrosion Inhibitions Of Steel In Acidic Medium By Some Aniline Derivatives

Author(s): El Sayed H. El Ashry, Ahmed El Nemr, Sami A. Esawy, Safaa Ragab

Quantum chemical parameters of some aniline derivatives (obtained by AM1, PM3, MINDO/3 and MNDO semi-empirical SCF calculations in gas and aqueous phases) have been correlated to corrosion inhibition efficiency of steel in aqueous acidic medium in order to search for possible correlations between corrosion inhibition efficiency and structural properties as well as to estimate the corrosion inhibition of some related structures. Geometric structures, total negative charge on the molecule (TNC), highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital (ELUMO), core-core repulsion (CCR), dipole moment (μ), total energy (TE), and linear solvation energy terms, molecular volume (Vi) and dipolar-polarization (π*) were correlated to corrosion inhibition efficiency. The correlation between quantum parameters and experimental inhibition efficiency has been validated by single point calculations for the semiemperical AM1 structures using B3LYP/6-31G* as a higher level of theory. Equations were proposed using linear regression analysis to calculate corrosion inhibition efficiency. The agreement with the experimental data was found to be satisfactory; the standard deviations between the calculated and experimental results ranged between ±0.03 to ±2.37 and ±0.02 to ±2.74 for gas phase and aqueous phase, respectively. The inhibition efficiency was closely related to orbital energies ELUMO in most cases. The proposed equations were applied to predict the corrosion inhibition efficiency of some related structures to select molecules of possible activity from a presumably proposed library of compounds.