Two Novel Benzodiazepines as Corrosion Inhibitors for Carbon Steel in Hydrochloric Acid: Experimental and Computational Studies

Abstract

Two new benzodiazepine derivatives namely, 1-ethyl-4-(2-oxopropylidene)-1,2,4,5-tetrahydro-2H-1,5-benzodiazepine-2-one (BZD-1) and 1-octyl-4-(2-oxopropylidene)-1,2,4,5-tetrahydro-2H-1,5-benzodiazepine-2-one (BZD-2) have been synthesized and used as corrosion inhibitors for carbon steel in acidic solution (1 M HCl). Corrosion inhibition evaluation was performed using weight loss, electrochemical techniques [potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS)], quantum chemical calculations, and molecular dynamic (MD) simulations. The results showed that both compounds are good corrosion inhibitors for carbon steel in 1 M HCl medium; their inhibition efficiency increased with inhibitor concentration. In addition, the results obtained from above methods reveal that BDZ-2 is an excellent inhibitor. It gives a maximum inhibition efficiency of 96.63% at 10−3 M and inhibits corrosion by adsorbing at the carbon steel surface. EIS measurements showed that the charge transfer resistance increases, whereas the double-layer capacitance decreases with the inhibitor concentration. Polarization studies showed that BDZ-1 and BDZ-2 are mixed type. The tested inhibitors have been adsorbed on the carbon steel surface according to Langmuir isotherm adsorption model. The experimental results are in reasonably close agreement with quantum chemical parameters calculated at DFT/B3LYB/3-21G and the molecular dynamic simulations results.