Interaction of Imidazoline Compounds with Fen(n1−4 Atoms) as a Model for Corrosion Inhibition:  DFT and Electrochemical Studies

The corrosion inhibition properties of 2-methylimidazoline (MIMD) and N-methyl-2-methylimidazoline (MMIMD) were studied by density functional theory (DFT) and electrochemical methods. The interaction of imidazoline molecules with the iron atoms was studied by DFT as a model for a corrosion inhibition process. DFT results explain why the imidazoline moieties favor the perpendicular adsorption, while their protonated species adsorb in parallel position over the metal surface. The electrochemical results show that although both perform as good inhibitors, MMIMD is better than MIMD because the former contains a methyl substituent in the ring which facilitates a strong adsorption on the metal surface. Furthermore, the delocalization (N1C2N3) region of the compounds that are involved in the corrosion inhibition process was analyzed by theoretical calculation, showing that the higher occupied molecular orbitals of the compounds have adequate symmetry to interact with the lower unoccupied molecular orbital of the metal. This theoretical prediction is in good agreement with the electrochemical results that MMIMD has a greater effect on corrosion inhibition than MIMD, because the methyl group in the imidazoline ring considerably increases the formation of the inhibitor film over the metallic surface and as a result a low Gibbs free energy value was obtained for the MMIMD film.