Experimental and theoretical investigation on the anti-corrosion characteristics of pyridine-substituted benzothiazole derivatives for mild steel in aqueous HCl.

Three new 2-(2-pyridyl)benzothiazole derivatives, namely 2-(benzothiazol-2-yl)pyridin-3-amine (APYBT), 2-(benzothiazol-2-yl)pyridin-5-ol (HPYBT) and 2-(pyridin-2-yl)benzothiazole (PYBT), have been synthesized. Those are tested for their potentiality to impart corrosion resistance to mild steel exposed to 1 M aqueous HCl. Both electrochemical and gravimetric experiments establish the studied benzothiazole (BT) derivatives as promising corrosion inhibitors, with APYBT standing out as the most effective one exerting more than 97% inhibition efficiency at 1 mM concentration. PYBT exerts the least inhibitory performance. The electron donating property of the amine group present on the pyridine moiety in APYBT could be responsible for the superiority of APYBT as a corrosion inhibitor among the three. A potentiodynamic polarization study revealed that the inhibitors could retard both the cathodic and anodic reactions. The adsorption of the inhibitors on metal surfaces follows the Langmuir adsorption isotherm. SEM images provide visual confirmation of the protection of mild steel surfaces from corrosion in the presence of the studied benzothiazole (BT) derivatives. The interaction pattern between the mild steel and the inhibitors is explored using results derived from density functional theory (DFT) calculations. Variation of the interaction energy as obtained from molecular dynamics (MD) simulation confirms the corrosion inhibitory trend. Fukui index calculation enables the role played by the substituent group towards the relative electron donation/acceptance properties of the atoms present at the different parts of the inhibitor molecule.