Towards Discovery of Ecological Inhibitor for Corrosion of Mild Steel in HCl Medium: trans-Anethole—the Molecule Responsible for Inhibitory Efficiency of Essential Oils Extracted from Leaves, Seeds, and Bulbs of Foeniculum vulgare

The obtained results allowed to reveal the inhibition properties of the essential oils of Foeniculum vulgare and to identify the major molecule—trans-anethole that enters into their composition. In this work, an isolated molecule of trans-anethole was tested in order to confirm its responsibility for a high inhibition efficiency and to study its adsorption mechanism. The inhibition efficiency of this natural molecule was evaluated by using such techniques as electrochemical polarization, impedance spectroscopy, and weight loss measurements. A protective layer formed on the mild steel surface was analyzed by scanning electron microscopy. This study showed a maximal inhibitory efficiency at 1.0 × 10–3 M. The essential oils of Foeniculum vulgare were found to be a mixed type inhibitor that adsorbs on the metal surface by physisorption and is resistant to high temperatures. Finally, the results obtained allowed not only to determine the molecule responsible for a good anticorrosive activity of three oils extracted from three parts of Foeniculum vulgare, but also to obtain a new strong ecological inhibitor.