Eco-friendly synthesis, biological activity and evaluation of some new pyridopyrimidinone derivatives as corrosion inhibitors for API 5L X52 carbon steel in 5% sulfamic acid medium

Some new pyridopyrimidinones derivatives (PPDs) namely (E)-2-(hexadecylthio)-8-(4-methoxybenzylidene)-5-(4-methoxyphenyl)-1,2,3,6,7,8-hexahydro-4H-cyclopenta[5,6] pyrido[2,3-d] pyrimidin 4 -one (Compound I) and (E)-8-(4-methoxybenzylidene)-5-(4-methoxyphenyl) -2-thioxo-1,2,3,6,7,8-hexahydro-4H-cyclopenta [5,6] pyrido [2,3-d] pyrimidin-4-one (Compound II) were synthesized and characterized by IR, ¹H-NMR, ¹³C-NMR and mass spectroscopy. The inhibition behavior of these derivatives for the corrosion of API 5L X52 carbon steel in 5% sulfamic acid solutions were considered by various electrochemical methods such as potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques, theoretically by quantum chemical calculations by using DFT method and molecular dynamic simulation (MD). PP curves presented that the PPDs act as mixed type inhibitors. By increasing PPDs compounds concentrations, the inhibition efficiency increases. The adsorption of PPDs follows Langmuir adsorption isotherm. Excellent agreement was established between the quantum chemical parameters and the experimental data.