Synthesis, characterisation and corrosion inhibitory study of meldrum's acid thiosemicarbazone: weight loss, SEM-EDX and DFT.

Abstract

Meldrum's acid thiosemicarbazone derivative, 2,2-dimethyl-5-(4-nitrobenzylidene)-1,3-dioxane-4,6-dione bis(4-ethyl-3-thiosemicarbazone) (4NMATSC), was successfully synthesised and characterised using the attenuated total reflectance-Fourier transform infrared (ATR-FTIR), nuclear magnetic resonance (NMR), ultraviolet–visible (UV–Vis) spectroscopies, and an elemental analyser. From the weight loss technique and SEM-EDX mapping analysis, 4NMATSC was verified to be a competent corrosion inhibitor in HCl by forming a protective layer on the surface of mild steel via adsorption. The effectiveness of the inhibitor increased as the concentrations of the inhibitor increased. The corrosion inhibitory effectiveness was 68.88 % at the highest concentration of 5 ppm. The density-functional theory (DFT) study revealed that the 4NMATSC was more favourable to nucleophilic attack through C[dbnd]S (covalent bond) to the mild steel surface to form an adsorption layer on the mild steel surface. Besides that, the values of ionisation potential, electron affinity, electron donating ability, and electron accepting ability deduced that the compound was preferred to donate electrons as compared to back-donating to the mild steel surface.