Study of the effect nitro and hydroxyl substituents of two imidazopyridines derivatives on inhibitory efficacy: combining theoretical and experimental study (part A)

The present study was devoted to the investigation of the effect of NO 2 and OH groups on the structure of two imidazopyridines, namely: (E)-N-(7-methyl-2-phenylimidazo[1,2-a]pyridin-3-yl)-1-(4-nitrophenyl)methanimine (Imid1) and (E)-4-(((7-methyl-2-phenylimidazo[1,2-a]pyridin-3-yl)imino)methyl)phenol (Imid2) on the corrosion inhibition efficiency of steel in an acidic medium, to remediate mild steel in hydrochloric acid. The evaluation of this activity was revealed using several experimental techniques such as weight loss measurements (WL), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), UV–visible spectroscopy study, surface characterization by SEM, as well as the impact of temperature and concentration on the inhibition efficiency for two inhibitors. The results obtained from these techniques show that the inhibition efficiency is reduced by the effect of the nitro electron-withdrawing group (NO 2 ) in the Imid1 molecule, but increased by the presence of the donor group (-OH) in the Imid2 molecule. The comparison of the results obtained by UV–visible spectroscopy of the inhibited and uninhibited electrolyte provided evidence for the formation of an Fe-ligand complex of two imidazopyridine molecules in 1 M HCl. Surface morphological studies by SEM revealed a uniform surface in the presence of Imid 1-2 , in contrast to a destroyed surface in the absence of the inhibitors. Finally, the results of DFT and MDS simulations are in good agreement with the experimental data and showed that the obtained order of the inhibition efficiency is always respected (Imid2 > Imid1). Graphical abstract