Some ethinylquinoxalines as corrosion inhibitors of steel in hydrochloric acid

• A.G. Berezhnaya, V.V. Chernyavina, I.I. Krotkii and A.V. Gulevskaya

Southern Federal University, ul. Zorge 7, 344090 Rostov-on-Don, Russian Federation

Abstract: The protective effect of 2-chloro-3(p-tolylethynyl)quinoxaline (I), 2,3-bis((4-methoxyphenyl)¬ethynyl)quinoxaline (II), 2-(4-methoxyphenyl)-3-(p-tolylethynyl)quinoxaline (III) and 2,3-bis(phenylethynyl)quinoxaline (IV) as inhibitors of acid corrosion of low-carbon steel (St3) in 1 M hydrochloric acid in the temperature range of 25 80°C has been studied. At a temperature of 25°C and a concentration of 0.1 mmol/l, the protective effect of the ethynylquinoxaline derivatives ((I–IV)) was found to be 82–92% depending on the structure. When the temperature increases to 60°C, the efficiency decreases to 35–57%. The studied compounds increase the value of the effective activation energy of corrosion and block a fraction of the steel surface upon adsorption. It is shown that the adsorption of the studied ethynylquinoxaline derivatives is described by the Langmuir isotherm. It has been established that compounds I and II are characterized only by chemical adsorption, while compounds III and IV exhibit both physical and chemical adsorption. Ethinylquinoxaline derivatives reduce the rates of cathodic and anodic reactions, and practically do not change the polarizability and mechanism of the processes. A good correlation of efficiency with the calculated parameters of the molecules obtained within the scope of the density functional theory (DFT) B3LYP/3-21G has been found. The best correlation is realized between the protective effect and such calculated parameters as the dipole moment, the sum of effective charges, the energy difference, hardness and softness. The best in this series of inhibitors is 2,3-bis((4-methoxyphenyl)ethynyl)quinoxaline. Compound II is characterized by the highest values of the dipole moment, energy difference and softness, as well as lower values of the sum of effective charges and hardness. It has been shown that the correlation coefficients of the linear relationships “protective effect–calculated characteristics” decrease with an increase in temperature.

Keywords: acid corrosion, inhibitor, ethynylquinoxaline derivatives, quantum chemical calculation

Int. J. Corros. Scale Inhib., 2025, 14, no. 1, 256-268
doi: 10.17675/2305-6894-2025-14-1-16

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