Synthesis and Characterization of Two Pyridazine N-Aryl Derivatives as Corrosion Inhibitors for Carbon Steel in 1 M HCl: Electrochemical, Surface Characterization and Theoretical Studies.

The present study explores the corrosion inhibition efficiency of two newly synthesized pyridazine N-aryl acetamide derivatives PDZ-PS2 (2-(4-(2-chlorobenzyl)-3-methyl-6-oxopyridazin-1(6H)-yl)-N-(2,6-dimethylphenyl)acetamide) and PDZ-PS3 (2-(4-(2-chlorobenzyl)-3-methyl-6-oxopyridazin-1(6H)-yl)-N-phenylacetamide) on carbon steel in 1 M HCl solution. The structures of the two newly synthesized compounds were confirmed using NMR 13 C, 1 H, IR and mass spectrometry analyses. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) analyses revealed a substantial increase in charge transfer resistance from 36.66 Ω·cm 2 (blank) to 458.90 Ω·cm 2 for PDZ-PS2 and 394.30 Ω·cm 2 for PDZ-PS3 at 10 -3 M, corresponding to inhibition efficiencies of 92.01% and 90.08%, respectively. The corrosion current density decreased markedly from 454.92 μA·cm -2 (blank) to 36.62 μA·cm -2 and 45.13 μA·cm -2 for PDZ-PS2 and PDZ-PS3 , confirming mixed-type inhibition behaviour. Adsorption followed the Langmuir isotherm, with high adsorption constants (K ads = 2.97 × 10 5 and 1.86 × 10 5 M -1 ) and negative free energies (ΔG° ads = −41.20 and −40.04 kJ·mol -1 ), indicating a spontaneous adsorption process involving mixed physical and chemical interactions, with chemisorption contribution. SEM and EDS analyses confirmed the formation of a compact protective layer on the steel surface. Monte Carlo simulations showed strong adsorption on the Fe(110) surface, with high binding energies of 530.39 kJ·mol -1 for PDZ-PS2 and 551.97 kJ·mol -1 for PDZ-PS3, confirming strong inhibitor–surface interactions. Overall, PDZ-PS2 exhibited slightly superior performance, demonstrating the strong corrosion protection potential of pyridazine-based acetamide derivatives in acidic environments.