Electrochemical and Theoretical Studies of Adsorption and Corrosion Inhibition of N,N′-Bis(2-hydroxyethoxyacetophenone)-2,2-dimethyl-1,2-propanediimine on Low Carbon Steel (API 5L Grade B) in Acidic Solution

Schiff base N,N′-bis­(2-hydroxyethoxyacetophenone)-2,2-dimethyl-1,2-propanediimine (H₂(hppnptn)) as corrosion inhibitor for API 5L grade B low carbon steel in hydrochloric acid solutions has been studied using electrochemical techniques and surface techniques. Results showed that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface. Thermodynamic parameters for adsorption and activation processes were determined. Polarization data indicated that this compound acts as mixed-type inhibitors, and the adsorption isotherm basically obeys the Langmuir adsorption isotherm. The calculations of reactivity indices of H₂(hppnptn) such as the localization of frontier molecular orbitals, <i>E</i>_<i>HOMO</i>, <i>E</i>_<i>LUMO</i>, energy gap (Δ<i><i>E</i></i>), dipole moment (<i>D</i>), hardness (<i>η</i>), softness (<i>σ</i>), the fractions of electrons transferred (Δ<i>N</i>), electrophilicity index (<i>ω</i>), total energy change (Δ<i><i>E</i></i>_<i>T</i>), and natural bond orbital (NBO) charge distributions together with local reactivity by means of Fukui indices were used to explain the electron transfer mechanism between the H₂(hppnptn) molecules and the steel surface