Corrosion Inhibition Study of a Heterocyclic Schiff Base Derived from Isatin

Abstract

A Schiff base, 3-(phenylimino)indolin-2-one, was successfully obtained from the condensation reaction of isatin and aniline in absolute ethanol with a yield of 72%. The ligand was successfully characterized via physical and spectroscopic techniques namely melting point, Elemental Analysis (C, H, N), 1H Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) Spectroscopy. The corrosion inhibiting property of the Schiff base and that of a mixture of its starting materials on mild steel in 1 M HCl solution was studied through Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR). The concentration of the Schiff base and the precursor molecules were varied from 1 x 10-3 M to 1 x 10-5 M. The results showed that the percentage of inhibition efficiencies increased with the increase of compound’s concentrations. Comparing the two sets of results for the Schiff base and the mixture of its starting materials, it was shown that the Schiff base was a much better inhibitor than the mixture of the starting materials, clearly indicating the importance of the presence of imine group (C=N) bearing lone pairs of electrons and π electrons in corrosion inhibition.