Effect of substituents on the inhibitive properties of newly synthesized 5‐benzoyl‐4‐methyl‐1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives against mild steel corrosion in an acidic medium

Inhibition performance of three newly synthesized 1,5‐benzodiazepine derivatives with 4‐methoxybenzoyl (methoxyBBD), 3‐methylbenzoyl (methylBBD), and 2‐chlorobenzoyl (chloroBBD) groups was investigated against mild steel corrosion in 1 M hydrochloric acid. The potentiodynamic polarization, electrochemical impedance spectroscopy, and adsorption isotherms were used for characterization of the corrosion processes. Surface morphology was studied by scanning electron microscope (SEM). Quantum chemical calculations were carried out to establish the active sites of the inhibitors. The results show that the inhibitors inhibit mild steel corrosion and their inhibition efficiencies (IE) increase with the increase in concentration. The methoxyBBD shows a higher inhibiting effect with IE of 89.13% at 10−3 M, followed by methylBBD. All three inhibitors act as mixed‐type inhibitors with predominant control of cathodic reaction for chloroBBD and their adsorption obeys Langmuir isotherm. The SEM analysis confirms the inhibitors' adsorption on the mild steel surface. The active sites of the inhibitors were effectively established using the density functional theory method on the basis of natural atomic charge, highest occupied molecular orbital, and the lowest unoccupied molecular orbital frontier molecular orbitals. The experimental and quantum results prove the inhibition performance trend of the inhibitors as follows: methoxyBBD > methylBBD > chloroBBD.