Experimental and Theoretical Studies on the Corrosion Inhibition Potentials of some Anisole derivatives for Mild Steel

The inhibitory and adsorption potentials of 2-(4-methoxybenzylideneamino) acetic acid (MBDAC), 2-hydroxy-3-methoxybenzaldehyde (HMBA) and 4-methoxybenzaldehyde (MBA) were studied using experimental (gravimetric and gasometric) and computational chemistry simulation approaches. The results obtained from the experimental approach revealed that the trend for the inhibitory potentials of the three anisoles is HMBA > MBDAC > MBA. The observed trend is attributed to the structural differences resulting from the introduction of -OH, =O and NCH2CO2H substituents into the respective compounds. The adsorption of the three inhibitors on mild steel surface is spontaneous and supported the mechanism of chemical adsorption. Computational chemistry simulations was carried out by comparing calculated quantum chemical parameters (the energy of the frontier molecular orbitals, the energy gap, dipole moment and logP) of the studied anisoles in gas and aqueous phases with experimentally obtained % inhibition efficiencies. The tests gave excellent correlations for PM6, PM3, AM1, RM1 and MNDO Hamiltonians. Correlations between experimental and predicted inhibition efficiencies were also excellent. Local selectivity study using the Fukui function and global softness indices indicated that the likely sites for electrophilic and nucleophilic attacks are in the enol bonds of the inhibitors.