Synthesis of a Novel Pyrimidine Compound and Evaluation of Its Corrosion Inhibition Performance for Carbon Steel in 1 M HCl Solution: Spectral Characterization, Electrochemical Studies, SEM/EDX Analyses, DFT Calculations, and Monte Carlo Simulations

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Abstract
A novel heterocyclic compound, 6-(tert-butyl)-4-phenyl-3,4-dihydropyrimidine-2(1H)-thione (TPDP), was synthesized via two distinct methods: a cyclocondensation reaction of (E)-4,4-dimethyl-1-phenylpent-1-en-3-one and a one-pot reaction involving thiourea, benzaldehyde, and pinacolone. The compound's structure was elucidated using standard spectroscopic techniques, including 1H NMR, 13C NMR, IR, and mass spectrometry. Given that organic compounds containing heteroatoms (N, S, O) are known to be effective corrosion inhibitors, this study evaluated TPDP's potential to inhibit corrosion of carbon steel (CS) in 1 M hydrochloric acid solution. Electrochemical measurements, including polarization curves and electrochemical impedance spectroscopy, coupled with theoretical studies, revealed that TPDP's inhibition efficiency increases with concentration, reaching 94% at 10−3 M. TPDP acts as a mixed-type inhibitor, forming a protective film on the metal surface. The Gibbs free energy of adsorption (−33.73 kJ/mol) indicates a physicochemical adsorption mechanism, consistent with the Langmuir adsorption isotherm. TPDP remains effective at elevated temperatures. Scanning electron microscopy (SEM), density functional theory (DFT), and Monte Carlo (MC) simulations further corroborate TPDP's robust inhibitory performance.

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