Synthesis and characterization of new quinoxaline derivatives of 8- hydroxyquinoline as corrosion inhibitors for mild steel in 1.0 M HCl medium

Two newly substituted quinoxalines derivatives of 8-hydroxyquinoline, namely 1,4-bis- ((8-hydroxyquinolin-5-yl)-methyl)-6-methylquinoxalin-2,3-(1H,4H)-dione (Q-HNHyQ) and 1,4-bis-((8-hydroxyquinolin-5-yl)-methyl)-quinoxalin-2,3-(1H,4H)-dione (Q- CH₃NHyQ), were synthesized and characterized by ¹H and ¹³C NMR spectroscopy. Their inhibitory performance was investigated against the corrosion of mild steel in 1 M hydrochloric acid medium by various corrosion monitoring techniques, such as weight loss, Tafel polarization and electrochemical impedance spectroscopy (EIS). It was found that the studied compounds exhibit a very good performance as corrosion inhibitors for mild steel corrosion in 1 M HCl. The inhibition efficiencies obtained from all employed methods are in good agreement with each other. It has been determined that the adsorption for the studied inhibitors on mild steel complies with the Langmuir adsorption isotherm at all studied temperatures. Potentiodynamic polarization studies have shown that the studied compounds act as mixed-type inhibitors toward mild steel. Scanning electron microscopy (SEM) was performed and discussed for surface study of uninhibited and inhibited mild steel samples.