Some imidazolines as inhibitors of steel corrosion in hydrochloric acid

New imidazoline derivatives were studied as steel corrosion inhibitors in hydrochloric acid at 20-80 degrees C. Imidazoline derivatives were conventionally divided into two groups. In one group, namely, aminoethyllaurylimidazoline, aminoethylmyristylimidazoline, aminoethylpalmitylimidazoline, and aminoethylstearylimidazoline, the compounds differ in the length of the hydrocarbon radical. Another group included compounds that differed by a functional group: aminoethyloleylimidazoline, hydroxyethyloleylimidazoline, diethylenediaminooleylimidazoline, and bis[oleylimidazoline]ethylene. The efficiency of imidazoline derivatives was evaluated by the gravimetric method, polarization curves, and electrochemical impedance spectroscopy. Quantum-chemical calculations were performed by the Hartree-Fock method. It was found that imidazolines which differ in the length of the hydrocarbon radical are the best acid corrosion inhibitors. In the temperature range studied, they provide 92-99% protection of steel. The degree of steel protection by imidazolines of the second group varies within 80-98%, depending on the nature of the compound and temperature. The imidazolines studied are mixed type inhibitors. It was shown that all the inhibitors increased the effective activation energy of the corrosion process. The degree of steel surface coverage with inhibitors was estimated. At all the temperatures studied, we attempted to relate the protective effect of the inhibitors to the calculated parameters: the dipole moment, the HOMO and LUMO energies, the difference in these energies, the hardness and softness of the compounds, the total electron density on the heteroatoms, and electronegativity. A correlation between the protective effect of the additives and the dipole moment and electronegativity was identified.