LAUSR

Abstract In the present work, we investigated three methoxy-substituted phenylthienylbenzamidine derivatives namely: monocationic 2,5-diarylthiophenes namely; 2-(4-amidinophenyl)-5-(4-methoxyphenyl)thiophene hydrochloride salt (MA-1313), 2-(4-amidinophenyl)-5-(3,5-dimethoxyphenyl)thiophene hydrochloride salt (MA-1314), 2-(4-amidino-3-fluorophenyl)-5-(3,5-dimethoxyphenyl)thiophene hydrochloride salt (MA-1216) as corrosion inhibitors for C-steel in 1 M HCl using weight loss (WL), potentiodynamic (PP) polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), surface examinations by energy dispersion spectroscopy (EDX) and scanning electron microscopy (SEM). Theoretical studies such as quantum chemical and molecular simulations studies were used to support the experimental findings. The experimental results revealed that the effectiveness of thienyl benzamidine derivatives increases with increasing the concentration of inhibitors in test solution, while it reduces as the temperature increases. The inhibition efficiency (%IE) of MA-1313 reaches to 95% at 21 × 10−6 M by EFM tests. The adsorption of the studied phenylthienylbenzamidine derivatives on the surface of C-steel obeys Langmuir adsorption isotherm. By calculating some relevant thermodynamic parameters, the adsorption-free energy values for investigated inhibitors have been obtained and discussed. The adsorption of the investigated compounds on C-steel was spontaneous process and rises in the same trend as the effectiveness of inhibition. Polarization curves indicated that the studied cationic 2,5-diarylthiophenes are mixed-type inhibitors, but mainly in the cathodic region than anodic domain. There is strong consensus between the results obtained from chemical and electrochemical methods.