Theoretical and Experimental Studies on the Corrosion Inhibition Potentials of 2-((6-Methyl-2-Ketoquinolin-3-yl)Methylene) Hydrazinecarbothioamide for Mild Steel in 1 M HCl

Novel modified coumarin bearing thiosemicarbazide pendant moiety prepared by the reaction of 3-(6-methyl-2-ketoquinoline)methanal with thiosemicarbazide through a condensation reaction. The synthesized coumarin namely 2-((6-methyl-2-ketoquinoline-3-yl)methylene) hydrazinecarbo-thioamide (MKMHCT) was characterized using spectroscopic techniques (proton and carbon 13 nuclear magnetic resonance and Fourier transform infrared). The corrosion inhibition of mild steel in 1 M hydrochloric acid solution by MKMHCT was investigated using the gravimetric method, scanning electron microscopy, and quantum chemical calculations. The obtained findings indicated that MKMHCT can inhibit the mild steel corrosion in a hydrochloric acid environment. The highest inhibition efficiency obtained from gravimetric techniques was 95.84% at the inhibitor concentration of 0.005 M. The adsorption of the studied inhibitor molecules on the mild steel surface was found to obey the Langmuir adsorption isotherm. Density functional theory (DFT) revealed an excellent correlation with experimental inhibitive performance. The frontier molecular orbital energies, i.e., Highest Occupied Molecular Orbital (HOMO), Lowest Unoccupied Molecular Orbital (LUMO), and other parameters were in harmony with methodological findings. Mulliken charges indicated that the inhibitor molecules are adsorbed on the surface of mild steel via coordination bonds between the iron atoms on the mild steel surface and the pairs of electrons of the nitrogen, oxygen and sulfur atoms.