6-Nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione (NQPr) – a novel corrosion inhibitor for mild steel in hydrochloric acid environment

Abstract

The novel synthesis of 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione, and its corrosion inhibition effect on mild steel in 1.0 M HCl solution was evaluated through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (Tafel), gravimetric and density functional theory (DFT) methods. The changes of corrosion current density and impedance modulus of mild steel in different concentrations of corrosion inhibitor solutions showed that the 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione presented a valid protective effect on mild steel in 1.0 M HCl environment. The inhibition efficiency of 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione on mild steel increases by increasing its concentration. Results showed that 6-chloro-1,4-di(prop-2-yn-1yl)quinoxaline-2,3(1H,4H)-dione acted as mixed type inhibitor. The 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione exhibited the maximum inhibition efficiency of about 93% at a concentration of 1.0×10 -3 M. Adsorption of 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione obeyed the Langmuir adsorption isotherm model. Gibbs free energy of adsorption (ΔG ads ), adsorption constant (K ads ) and activation energy (E a ) values showed that the inhibitor 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione is strongly and spontaneously adsorbed on the mild steel surface/electrolyte interface. The inhibitive properties of 6-nitro-1,4-di(prop-2-yn-1-yl)quinoxaline-2,3(1H,4H)-dione obtained from experimental method was supported by DFT. Numerous parameters were computed and discussed in order to describe its adsorption behavior.