Experimental and quantum chemical investigations of the corrosion inhibition effect of bis carbothioamide derivatives synthesized from isothiocyanate and tetrazole derivatives

Three Biscarbotioamides, namely, N-2-fluorophenyl-hydrazine-1,2-biscarbotioamide (2F-PhenHC), N-benzylhydrazine-1,2-biscarbotioamide (BenzHC) and N-cyclohexylhydrazine. -1,2-biscarbotioamide (ChexHC) were investigated as corrosion inhibitors for mild steel in 1.0 M HCl solution using weight loss method, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results revealed that they all inhibit corrosion and their %inhibition efficiencies (%IE) follow the order: BenzHC T>ChexHC>2F-PhenHC. The thermodynamic parameters obtained support a physical adsorption mechanism and the adsorption followed the Langmuir adsorption isotherm. A theoretical calculation study through utilizing using the theory of functional density (DFT) at the B3LYP functional by using 6-311++g (2d, 2p) methods in gas and water phase of neutral and protonated forms of molecules. The quantum chemical parameters/descriptors, namely, energy gap (E), dipole moment (DM), electrophilicity (ω), proton affinity (PA), Polarizability (a), hyperpolarizability () highest occupied and lowest unoccupied molecular orbital energy (EHOMO, ELUMO), electronegativity (χ), hardness (η) and softness (σ), were calculated and correlated with the experimental inhibition efficiencies (%IE). It was observed that the theoretical and experimental results obtained supported with the physical adsorption mechanism. Both the theoretical and experimental results are in good agreement. In addition to, tetrazole (T) and some tetrazole derivatives: 5-mercapto-1-methyl tetrazole (5-Mc-1-Me-T), 5-mercapto-1-phenyl tetrazole (5-Mc-1-Ph-T), 5-phenyl tetrazole (5-Ph-T) and 5-amino tetrazole (5-NH2-T) for neutral and protonated forms in gas and water phase have been performed and the relationship between quantum chemical parameters and experimental inhibition efficiencies were discussed.