A Computational Study of Quinoline Derivatives as Corrosion Inhibitors for Mild Steel in Acidic Medium

The corrosion inhibition efficiency of three quinoline derivatives namely; ethyl 2-(((8-hydroxyquinolin-5-yl)methyl)amino)acetate (QN1), 5-((benzylamino)methyl)quinolin-8-ol (QN2) and 5-(azidomethyl)quinolin-8-ol (QN3) on the mild steel in 1 M HCl was studied using density functional theory (DFT) calculations and quantitative structural activity relationship (QSAR) approach. The experimental inhibition efficiency were discussed in relation with molecular descriptors such as such as EHOMO (energy of the highest occupied molecular orbital), ELUMO (energy of the lowest unoccupied molecular orbital), band gap (BG), dipole moment (DM), chemical hardness (η), softness (σ), electronegativity (χ), electrophilicity (ω), global nucleophilicity (ɛ), electrons transferred from inhibitors to metal surface (ΔN), initial molecule-metal interaction energy (∆ψ), the energy change during electronic back-donation process (ΔEb-d), Molecular weight (MW), and Volume (V). The result showed that EHOMO, σ , ω, ΔN, ΔEb-d and ∆ψ increases as the percentage inhibition efficiency (%IE) increases. ELUMO, BG, η , DM, and ɛ decreases with increasing% IE, while χ , MW and V did not show any correlation with %IE. The QSAR model developed reproduced the observed corrosion inhibition efficiencies of these compounds well with a cross validation (CV. R2) value of 0.9994 and adjusted squared correlation coefficient (R2adj) value of 0.9988. The results obtained in the study are in good agreement with experimental inhibition efficiency results reported earlier in literature.