Corrosion inhibition of mild steel in acidic media using new oxo-pyrimidine derivatives: Experimental and theoretical insights

Abstract

Interesting results have been found for new compounds derived from oxo-pyrimidine to protect of mild steel (MS) in 1 M hydrochloric acid. These the compounds are 1-(5-(4-Methoxy-benzoyl)-4-(4‑methoxy-phenyl)-2-oxo-2H-pyrimidin-1-yl]-(4‑methoxy-phenyl)-urea (MMOM) and 1-(5-(4‑methoxy-benzoyl)-4-(4‑methoxy-phenyl)-2-oxo-2H-pyrimidin-1-yl)-3-(4-methlyphenyl)-thiourea (MMOPM). In this study, the impact of immersion time on inhibitor effectiveness was also investigated. Both substances function as mixed-type inhibitors, according to the electrochemical data. At 5 × 10−4 M and a 72-hour immersion duration, MMOM is more effective than MMOPM (98.42% vs. 94.49%). The Langmuir isotherm system provided the best match for both compounds, with chemisorption as the kind of adsorption. According to the findings of surface characterisation, both chemicals may be adsorbed on mild steel surfaces to reduce corrosion. Inhibitor simulations using density functional theory revealed that the protonated state is more reactive than the neutral state and coincides with experimental findings. The outcomes demonstrated that both compounds may be utilised as new mild steel corrosion inhibitors in harsh conditions and long-term immersion. The theoretical study, based on quantum chemical calculations of the compounds, performed by the DFT/BP86 method with a 6–311G(d,p) basis set by using Gaussian 09, Revision A.02 program, were also included to support experimental results. The various quantum chemical parameters such as EHOMO, ELUMO, chemical hardness and chemical softness, electronegativity of the investigated molecules were calculated, and their inhibition efficiency were discussed. The outcomes demonstrated that both compounds may be utilised as new mild steel corrosion inhibitors in harsh conditions and long-term immersion.