In silico evaluation for the design of coumarin-type compounds based on phenol and naphthol rings as a coating in carbon steel corrosion processes: DFT B3LYP calculations, synthesis and electrochemical characterization

Corrosion is a natural electrochemical process that converts metals into their most stable form, oxides. Coating metals with paints is done most effectively if oxide scales are removed, which is done by exposing the metals to corrosive media such as HCl, H2SO4, HNO3, and NaCl. However, corrosive solutions also attack the metal surface, and adding an inhibitor to the acid environment becomes necessary. Inhibitors can be inorganic or organic and are evaluated through techniques such as Potentiodynamic Polarization (PDP) and Impedance Spectroscopy (EIS). This work evaluated coumarin-type organic molecules compounds as potential corrosion inhibitors through the DFT B3LYP calculations of quantum descriptors. The results were analyzed using Principal Components Analysis (PCA), it is established that the values of inhibitory efficiency of 1, and 33, showed that the corrosion of the metallic surface which can be seen in the inhibitory efficiency values 1 (57,14 %) and 33 (82,86 %), it is evident that 33 has the highest effect respect other coumarins being identified as phenol and naphthol derivatives. These compounds were synthesized employing sequential reactions from the respective phenol: Pechmann cyclization, nitration, and reduction reactions. Then, the compounds were evaluated as anti-corrosive agents for carbon steel in the presence of 1.0 M HCl. The cathodic and anodic current densities in the HCl solution containing coumarin 1 exhibit lower values than the 33 and the Blank solutions. The obtained data reveals that as the amount of coumarins 1 (3.2 mg), and 33 (2.8 mg) increases, the corrosion current density (icorr) decreases to values of 3.08 and 4.90 mA.cm-2, respectively. These results were validated through the electrochemical evaluation of the molecules obtained by Potentiodynamic Polarization (PDP), Impedance Spectroscopy. (EIS) and Scanning Electron Microscopy (SEM).