Investigation of substituent position effects of Schiff base compounds on mild steel corrosion

In this study, three new Schiff base ligands namely 1-((1E)-((8-((2-hydroxybenzylidene)amino)naphthalen-1-yl)imino)methyl)naphthalen-2-ol (L1-2HB), 1-((1E)-((8-((3-hydroxybenzylidene)amino)naphthalen-1-yl)imino)methyl)naphthalen-2-ol (L2-3HB) and 1-((1E)-((8-((4-hydroxybenzylidene)amino)naphthalen-1-yl)imino)methyl)naphthalen-2-ol (L3-4HB) were synthesized through two-steps process via reflux-reaction. 1H Nuclear Magnetic Resonance (1H NMR) and Fourier Transform Infrared (FTIR) Spectroscopies were used to characterize the synthesized Schiff base ligands and the inhibitory effect of mild steel in 1.0 M hydrochloric acid (HCl) and 1.0 M sodium chloride (NaCl) solutions in the presence of varying concentrations of Schiff bases as corrosion inhibitor was investigated at room temperature using weight loss method. The existence of imine group in the range of 1620 – 1625 cm−1 on IR spectrum revealed the formation of the azomethine linkage indicating the desired compound was successfully achieved. These Schiff base compounds significantly inhibited mild steel corrosion in both solutions. The efficiency of inhibition was observed to improve as the inhibitor concentration was increased. Weight loss analysis confirmed that the Schiff base compounds have effective inhibitory abilities for mild steel in HCl and NaCl medium, with a maximum inhibition efficiency of 99 and 96 % at 0.1 M of additive concentration. The pattern of maximum inhibition efficiency for both solutions increase in the order of ortho>para>meta substituted. According to the experimental findings, it can be proposed that the Schiff base ligand (L1-2HB) containing electron donating substituent at appropriate position exhibited excellent inhibitory action on mild steel surface in the medium investigated.