Pyranpyrazole derivatives as novel corrosion inhibitors for mild steel useful for industrial pickling process: Experimental and Quantum Chemical study

In the present work three new corrosion inhibitors namely ethyl 6-amino-3-methyl-4-(p-tolyl)-2,4-dihydropyrano[2,3,C]pyrazole-5-carboxylate (EPP-1), ethyl 6-amino-3-methyl-4(phenyl)-2,4-dihydropyrano[2,3,C]pyrazole-5-carboxylate (EPP-2), ethyl 6-amino-3-methyl-4-(3-nitrophenyl)-2,4-dihydropyrano[2,3,C]pyrazole-5-carboxylate (EPP-3) were prepared, characterized and their corrosion inhibition properties on mild steel were investigated using gravimetric, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The surface morphology of the mild steel was examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). EPP-1 exhibited highest efficiency of 98.8% at 100 mg/L. AFM and SEM studies confirmed the formation of adsorbed film on the metal surface. The inhibitors followed the Langmuir adsorption isotherm. Density functional theory (DFT) was used to understand donor–acceptor relationship between inhibitors and metal. The orientation and binding energy of inhibitor molecules were investigated using molecular dynamic simulation (MD). A good relationship was obtained between theoretical and experimental results.