Green Synthesis of Rhodanine-Derived Inhibitors for Carbon Steel Corrosion Protection: DFT, Thermodynamic, and Surface Analysis

This study presents a green synthesis of three of (Z)-5-arylidene-rhodanine derivatives in an aqueous medium and evaluates their efficacy as corrosion inhibitors for carbon steel in 0.5 M H2SO4. The synthesis, optimized using ammonium acetate as a catalyst, yielded ten derivatives (3a–3c) with excellent efficiency (86–90% yield). Spectroscopic techniques (1H NMR, MS) and theoretical calculations confirmed the (Z)‑configuration of the products. Corrosion inhibition performance was assessed via weight loss studies, and scanning electron microscopy (SEM). Among the tested compounds 3c, 5-(4-hydroxy-3-methoxybenzylidene)-3-phenyl-2-thioxothiazolidin-4-one, exhibited superior inhibition efficiency (99.65% after 72 h), attributed to its strong chemisorption (ΔGads = −43.70 kJ/mol) and high equilibrium constant (Kads = 617.26 m3/mol). Density functional theory (DFT) calculations, revealing high EHOMO (–5.83 eV), low ELUMO (–2.37 eV), low energy gap (ΔEgap = 3.46 eV), and significant electron transfer (ΔN = 3.21 eV) for 3c, elucidated the molecular interactions promoting adsorption. Thermodynamic and kinetic analyses revealed an endothermic, non-spontaneous adsorption process, with 3c significantly increasing the activation energy (Eact = 85.40 kJ/mol). SEM confirmed the formation of a protective layer, minimizing surface degradation. These findings highlight the potential of rhodanine derivatives as eco-friendly, high-performance corrosion inhibitors for industrial applications.