Preparation, Spectral Characterization and Corrosion Inhibition Studies of (E)-N-{(Thiophene-2-yl)methylene}pyrazine-2-carboxamide Schiff Base Ligand

Abstract

The study described the preparation and characterization of thiophene/pyrazine Schiff base, (E)-N-{(thiophene-2-yl)methylene}pyrazine-2-carboxamide (HL) using melting point and micro (CHN) analysis; vibrational, nuclear magnetic resonance (1H- and 13C-NMR) and electronic (UV–Vis) spectroscopies. HL was also studied for adsorption and corrosion properties. The spectral data were consistent with tridentate bonding nature and enolimine tautomeric arrangement within the ligand assemblage giving credibility to its formation. Density functional theory (DFT) calculations correlated the investigational data, while its percentage inhibition efficiency (IE, %) increased with rise in concentration though declined with increase in temperature (T). The latter indicate that the inhibition proficiency (IP) with T was mixed adsorption, with physisorption dominating the corrosion inhibition process. Similarly, the adsorption of HL on the mild steel (ms) obeys Langmuir adsorption isotherm. However, the negative sign of $$\Delta G_{{{\text{ads}}}}^{^\circ }$$ and $$\Delta H_{{{\text{ads}}}}^{^\circ }$$ designates that HL adsorption on the ms surface in 1.0 M HCl was instantaneous and exothermic correspondingly. Furthermore, the scanning electron microscopy (SEM) data corroborates that HL hinders ms corrosion through the formation of protective layers on ms surfaces.