Carboxamide derivatives as new corrosion inhibitors for mild steel protection in hydrochloric acid solution

[Display omitted] •Carboxamide ligands used as effective corrosion inhibitors for mild steel in 1M HCl.•The order of inhibition efficiency for the two compounds is Hqcq > Hqpzc•EIS indicates that these compounds act via adsorption at metal/solution interface.•Adsorption of carboxamide ligands on mild steel surface obeys Langmuir’s isotherm.•Thermodynamic parameters (Ea, Kads, ΔG°ads) are calculated and discussed. In this study, the inhibitive performance of carboxamide ligands, (N-(quinolin-8-yl) quinoline-2-carboxamide), Hqcq; and (N-(quinolin-7-yl) pyrazine-2-carboxamide), Hqpzc, was examined under steady condition in HCl solution at 25 °C for mild steel. These carboxamides were synthesized using TBAB as green reaction medium. Electrochemical impedance spectroscopy (EIS) revealed that these inhibitors act via adsorption at metal/solution interface. The adsorption of inhibitors obeys the Langmuir adsorption isotherm. It is clear that Hqcq exhibits a better inhibitory performance presumably due to its uniform film and nearly planar and parallel arrangement on metal surface. The thermodynamic parameters (Ea, Kads, ΔG°ads) have also been calculated and discussed.