The effects of N-pendants and electron-rich amidine motifs in 2-(p-alkoxyphenyl)-2-imidazolines on mild steel corrosion in CO₂-saturated 0.5 M NaCl

Highlights: • A novel class of electron-rich imidazolines has been prepared. • The amidine motifs in imidazolines is in conjugation with alkoxyphenyl groups. • Inhibition of mild steel corrosion by the imidazolines in NaCl–CO₂ is compared. • Imidazolines cover most of the metal surface before reaching their CMCs. • At 40 °C (1 atm) and 120 °C (10 bar), imidazolines provided very good inhibition. - Abstract: A novel series of diethylenetetramine-(I), and tetraethylenepentamine-derived imidazolines (II) having p-octyloxy-, dodecyloxy and octadecyloxy-phenyl pendants as hydrophobes, have imparted very good inhibition of mild steel corrosion in CO₂–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar). Pendants to the ring-nitrogen of I and II showed no change in inhibition efficiencies, while the presence of electron-rich aromatic ring in conjugation with the amidine motifs and increasing hydrophobe chain lengths imparted increasing corrosion inhibition. The formation of an imidazoline film covering the metal surface is corroborated by an XPS study. The imidazolines cover the metal surface before reaching their critical molar concentrations