Exploring the efficacy of novel thiohydantoin derivatives with arylacetamide core as corrosion inhibitors for mild steel in acidic medium: insights from electrochemical analysis, comprehensive characterization, and quantum studies

Two new compounds of Thiohydantoin Derivatives N-(4-nitrophenyl)-2-((5-oxo-4,4-diphenyl-4,5-dihydro-1Himidazole-2-yl)thio) acetamide and N-(4-fluorophenyl)-2-((5-oxo-4,4-diphenyl-4,5-dihydro-1H-imidazole-2-yl) thio) acetamide symbolized by N - NOITAcetamide and N-FOITAcetamide respectively, were synthesized and characterized by NMR spectroscopy. Their effectiveness in inhibiting mild steel (M -S) corrosion in 1.0 M HCl at 298 K was investigated by potentiodynamic polarisation (PDP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), and surface examinations via energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) as well as X-ray photoelectron spectroscopy (XPS). Experimental results have been supported by theoretical studies such as Density Functional Theory (DFT) calculations and Monte Carlo (MC) simulation studies. All findings indicate that inhibitors have a considerable impact on lowering the rate of corrosion, and that the efficiency of the inhibitors rises with the concentration of the inhibitor. Experimental results revealed that the efficacy of the new thiohydantoin derivatives with an arylacetamide nucleus increased with increasing inhibitor concentration, where their inhibition efficiencies reached maximum values of 92.1 %, 94.1 %, for N - NOITAcetamide and N-FOITAcetamide, at 10 - 3 M, respectively. In addition, the i corr decreased with increasing concentration up to 85 mu A cm -2 and 58 for N - NOITAcetamide and N-FOITAcetamide respectively, with a blank as a reference of 1045 mu A cm -2 , while the efficacy reduces as the temperature increases. The activation and thermodynamic parameters indicated that these products act via chemical adsorption on the mild steel surface. Furthermore, the surface analysis (SEM, EDS, and XPS) confirmed the formation of a protective layer adsorbed on the mild steel surface. Polarization curves indicated that N - NOITAcetamide and N-FOITAcetamide are mixed -type inhibitors. Moreover, the quantum chemical calculation well supports the experimental results.