The Performance of Amino- and Hydroxy-Substituted Benzothiazoles in Inhibiting the Corrosion of Carbon Steel in HCl and the Molecular-Level Mechanisms

Graphical The corrosion inhibition of NH 2 and OH substituted benzothiazoles on carbon steel in 0.5 mol/L HCl was investigated. 0.0010 mol/L 2-amino-6-hydroxybenzothiazole demonstrated efficient and persistent performance. The adsorption followed Freundlich-Langmuir isotherm. The OH at 6th position extended negative potential region and enhanced coordination activity, resulting in favorable orbital distribution for flat adsorption and feedback bonds. In the pickling process and acidizing program for oil wells, the acidic corrosion of metals is a problem that needs to be addressed. Various acid corrosion inhibitors have been studied and used to mitigate the acidic corrosion of carbon steel. In this paper, the corrosion inhibition of 2-aminobenzothiazole (2 N-BT), 2-amino-4-hydroxybenzothiazole (2 N4O-BT), and 2-amino-6-hydroxybenzothiazole (2 N6O-BT) on carbon steel in 0.5 mol/L HCl was investigated using electrochemical and quantum chemical methods. All three molecules exhibited corrosion inhibition effects. Compared to 2 N-BT, 2 N4O-BT and 2 N6O-BT showed less sensitivity to the environmental conditions and the surface state of the metal. Among them, 0.0010 mol/L 2 N6O-BT demonstrated the highest and most persistent corrosion inhibition, exhibiting a mixed inhibition mechanism with cathodic inhibition dominance. The adsorption of 2 N6O-BT on the carbon steel surface was found to be non-uniform, preferentially adsorbing at certain active sites on the surface, following Freundlich-Langmuir thermodynamic characteristics. It showed initial strongly adsorbed points and weakly adsorbed regions. With continued adsorption of 2 N6O-BT, the differences between strongly adsorbed points and weakly adsorbed regions decreased. The introduction of hydroxyl groups, especially in 2 N6O-BT, extended the negative potential region and enhanced the coordination activity of the molecule, generating the orbital distribution that was advantageous to flat adsorption and the formation of feedback bonds. This provided a molecular structural basis for the excellent corrosion inhibition properties of 2 N6O-BT.