LAUSR

Abstract The synthesis of (E)-4-((p-tolylimino)methyl) phenol (TMPOL), (E)-4-((benzylimino)methyl) phenol (BMPOL) and (E)-4-((p-phenylimino)methyl) phenol (PMPOL) were carried out by the condensation reaction of 4-methylaniline, phenylmethanamine and aniline, respectively, with 4-hydroxybenzaldehyde. Molecular identities of the Schiff base compounds were probed using NMR (1H and 13C), Fourier transform infrared (FTIR) and mass spectroscopic techniques. The anticorrosion potency of the compounds was investigated for mild steel (MS) in 1 M HCl solution using electrochemical methods. Potentiodynamic polarization (PDP) data revealed that all three compounds were mixed-type inhibitors, with TMPOL showing remarkable cathodic effect at high inhibitor concentrations. Electrochemical impedance spectroscopy (EIS) data revealed improved adsorption of inhibitor species on mild steel surface at increased inhibitor concentrations with TMPOL, BMPOL and PMPOL reaching a maximum efficiency of 75, 88 and 74%, respectively. Scanning electron microscopy (SEM) reaffirmed the conditioning layer on the mild steel surface. Quantum chemical calculations provided molecular based explanations of the roles of heteroatoms and π electron centers on the corrosion inhibition activities of the studied compounds. The better anticorrosion activities of BMPOL compared to its isomeric compound (TMPOL) can be ascribed to the presence of a methylene linkage which enhanced the donor-acceptor interactions. The three inhibitors were inclined towards the Freundlich adsorption isotherm via a spontaneous chemical and physical adsorption of inhibitor molecules on the MS surface.