Experimental and computational approaches on the pyran derivatives for acid corrosion

Pyran derivatives namely ethyl 2-amino-4-(4-hydroxyphenyl)-6-(p-tolyl)-4H-pyran-3-carboxylate (HP), ethyl 2-amino-4-(4 methoxyphenyl)-6-(p -tolyl)-4H-pyran-3-carboxylate (MP) and ethyl 2-amino-4-(4-hydroxy-3,5-dimethoxyphenyl)-6-(p-tolyl)-4H-pyran-3-carboxylate (HDMP) were synthesized and characterized by FTIR and Mass spectroscopy. Weight loss and electrochemical measurements were done to study the corrosion mitigation of mild steel (MS) in 1 M sulphuric acid solution. The inhibition efficiency of the pyran derivatives (HP, MP and HDMP) increased by increasing their concentration to reach respectively a maximum value of 91.6 %, 92.5 % and 95.0 % at 2 mM for HP, MP and HDMP and their adsorption followed Langmuir isotherm. Pyran derivatives act as mixed-type inhibitors which will be known from the polarization measurements. The results of the EIS study suggest that these compounds inhibit corrosion by adsorption mechanism. Surface of the metal with and without inhibitors in acid medium was studied by SEM-EDS, XRD and AFM methods. Quantum chemical studies have been performed for the non-protonated and protonated forms of the inhibitors. The obtained results by MD simulations have revealed that the studied molecules bind onto iron area spontaneously with binding energies of 438.465 kJ/mol, 434.934 kJ/mol, and 456.854 kJ/mol for HP, MP and HDMP respectively.