Benzodiazepine Derivatives as Corrosion Inhibitors of Carbon Steel in HCl Media: Electrochemical and Theoretical Studies

New benzodiazepine derivatives, namely 8-Chloro-1,2,3,4,10,11-hyxahydrospiro[cyclohexane-1,11-dibenzo[1,4]diazipine] and 8-methyl-1,2,3,4,10,11-hyxahydrospiro[cyclohexane-1,11 dibenzo[1,4]diazipine] are heterocyclic and their inhibitive action against the corrosion of carbon steel in 1.0 M HCl solution was studied at 303 K by electrochemical impedance spectroscopy and polarization curves The results marked that the learned benzodiazepine product are good corrosion inhibitors to carbon steel in 1.0 M HCl medium, their inhibition efficiency increased with inhibitor concentration, and BND–Cl is slightly more effective than BND–CH₃. Potentiostatic polarization study showed that BND–CH₃ and BND–Cl are mixed-type inhibitors in 1.0 M HCl. Impedance experimental data disclose a frequency distribution of the capacitance, simulated as a constant phase element. The results obtained from electrochemical studies were in reasonable accordance. The adsorption of BND–Cl and BND–CH₃ on steel surface obeyed Langmuir’s adsorption isotherm. Thermodynamic data clearly proper that the adsorption mechanism of benzodiazepine products on carbon steel surface in 1.0 M HCl solution is physical adsorption which implies electrostatic forces among the electric charge or ionic charges at metal/solution interface and dipoles of the adsorbent verify by the a chemisorption. Quantum chemical calculations employ the Density Functional Theory (DFT) were performed on benzodiazepine products to define the link between molecular structures and their inhibition efficiencies. Furthermore, the structures mentioned are stimulated by the Monte Carlo simulation to comprehend the adsorption mechanism. Finally, the correlation among experimental and theoretical returns was discussed.