Experimental and theoretical investigation of 5-(5-bromothiophen- 2-yl)oxazole as a highly effective corrosion inhibitor for mild steel in 1 M hydrochloric acid

The present research article focuses on the utilization of 5-(5-bromothiophen-2-yl)oxazole as a potent corrosion inhibitor for mild steel in 1 M hydrochloric acid (HCl) solution. The corrosion inhibition behavior of the inhibitor was thoroughly examined using experimental gravimetrical measurements, and density functional theory (DFT) studies. To investigate the effect of varying conditions, the inhibitor's performance was studied at different temperatures (303, 313, 323, and 333 K) and immersion periods (1, 5, 10, 24, and 48 hours). Remarkably, 5-(5-bromothiophen-2-yl)oxazole exhibited an outstanding inhibition performance of 93.8% at an optimized inhibitor concentration of 0.5 mM, effectively mitigating mild steel corrosion in the aggressive 1 M HCl environment. To gain deeper insights into the inhibitor's inhibitive properties, quantum chemical calculations were performed. Frontier Molecular Orbitals (HOMO and LUMO), energy gap (Delta E=ELUMO-EHOMO), electronegativity, chemical softness, hardness, and the number of electron transfers (Delta N) were meticulously determined and analyzed. The findings revealed that nitrogen, oxygen, and sulfur atoms were the most favorable sites for coordination with iron atoms on the mild steel surface through electron donation to unoccupied d-orbitals of Fe atoms. The experimental data also supported the Langmuir adsorption isotherm model for the inhibitor's behavior. This comprehensive investigation provides valuable insights into the inhibitive mechanism of 5-(5-bromothiophen-2-yl)oxazole, bridging the gap between experimental observations and theoretical predictions, and presents promising prospects for its practical application in corrosion protection of mild steel in acidic environments.