Synthesis of fatty phenylthiosemicarbazide from underutilized Sesamum indicum seed oil: a promising corrosion inhibitor of carbon steel in developing country

Fatty phenylthiosemicarbazide (FP) was synthesized from Sesamum indicum seed oil (SO) via simple reaction mechanism, which was characterized using Fourier transform infrared and proton nuclear magnetic resonance (1HNMR). Fatty acid composition of SO was examined using gas chromatography (GC) coupled with flame ionization detector while FP was evaluated for its ability to inhibit corrosion in carbon steel using weight loss method. Quantum chemical computation using density functional theory was applied to gain theoretical insight on the inhibition capacity of FP. The result of the GC revealed the most dominant fatty acid in SO to be C18:2 (43.77%) while the least was C16:1 (0.10%). FP exhibited a corrosion inhibition efficiency of 62.55% at room temperature but increased to 99.57% at 303 K, which obeyed Langmuir isotherm. The $$\Delta G_{ads}^{^\circ }$$ value revealed the process to be spontaneous while both $$\Delta H_{ads}^{^\circ }$$ (− 1.088 kJ mol−1) and $$\Delta S^{^\circ }$$ (− 0.015 kJ mol−1 K−1) suggested an exothermic process. The lowest unoccupied molecular orbital and highest occupied molecular orbital were distributed over the molecule of FP with an activation energy of 25.606 kJ mol−1. The current study presents FP as a promising corrosion inhibitor, which can replace synthetic compounds from petrochemicals used as corrosion inhibitors in developing countries.