Synthesis of novel thiazole derivatives and their assessment as efficient corrosion inhibitors on mild steel in acidic medium

Abstract

This study presents synthesis of novel thiazole derivatives, 2′,4′-dimethyl-2-phenyl-[4,5′-bithiazole]-5-carboxylic acid (Th-A) and 4′-methyl-2,2′-diphenyl-[4,5′-bithiazole]-5-carboxylic acid (ThB) and rigorously characterized using ¹H and ¹³C NMR along with mass spectrometry. These compounds demonstrated remarkable inhibitory efficiencies of 85 % (Th-A) and 90 % (ThB) at 10⁻³ M, as revealed through electrochemical analyses, including EIS and PDP techniques and Weight loss analysis on mild steel immersed in 1 M HCl. The increase in charge transfer resistance R_ct from 13.23 Ω·cm² to 95.73 Ω·cm² for Th-A and 114.6 Ω·cm² for ThB confirms their ability to mitigate steel corrosion. The inhibitors exhibited a mixed-mode action with E_corr displacements below 85 mV and adhered to Langmuir adsorption isotherms, signifying their robust interaction with the metallic surface. Gibbs free energy of adsorption (ΔG_ads) indicates Th-A (−40.92) and ThB (−39.85) adsorbs physically and chemically over metal surface. The formation of a protective film, effectively mitigating corrosion, was further substantiated by atomic force microscopy (AFM), which highlighted a significant reduction in surface roughness to 52.35 nm for Th-A and 39.61 nm for ThB. Complementary density functional theory (DFT) computations provided theoretical validation of the adsorption and electronic attributes, aligning seamlessly with experimental outcomes. The calculated energy gaps ∆E of 0.9456 eV for Th-A and 0.8139 eV for ThB highlight their favourable electronic properties or adsorption. This synergistic approach underscores the superior efficacy of Th-A and ThB as potent corrosion inhibitors and offers a detailed mechanistic perspective, merging experimental insights with theoretical modeling to advance the understanding of corrosion protection strategies.