New spirocyclopropane derivatives: synthesis and evaluation of their performances toward corrosion inhibition of mild steel in acidic media

Developing environmentally friendly products is a modern science and an important task for today's chemistry and technology scholars. In the present research work, two new green chemical compounds, namely 1-benzoyl-6,6 dimethyl-2-phenyl-5,7 dioxaspiro[2.5]octane-4,8 dione (BMP) and 1-benzoyl-6,6-dimethyl-2-(4-nitrophenyl)-5,7-dioxaspiro[2.5]octane-4,8-dione (BMNP), have been synthesized and characterized. Their inhibition properties were investigated in hydrochloric acid solution (1.0 M HCl), for mild steel (MS) corrosion in different temperatures from 303 to 333 K, using, on the one hand, the experimental methods being electrochemical impedance spectroscopy, weight loss, as well as potentiodynamic polarization (PDP) techniques, and on the other hand, utilizing quantum chemical study, and Monte Carlo simulations. BMP and BMNP effect on the surface of MS have even been accentuated by scanning electron microscope. Experimental and theoretical results show that the two spirocyclopropane derivatives are good inhibitors in hydrochloric acid solution against the MS corrosion, and their inhibitory efficiencies (η%) are reaching values up to 91% and 95%, respectively, at a concentration of 10⁻³ M. BMNP is more effective than BMP owing to the NO₂ grouping which has resulted in a clear augment in the propensity for corrosion inhibition. The PDP curves reveal that BMP and BMNP are mixed type inhibitors. Adsorption of inhibitors onto the steel surface was described well by Langmuir isotherm. To fully understand the mechanism of BMP and BMNP inhibition toward the MS surface in 1.0 M HCl solution, Monte Carlo simulations and density functional theory were carried out and discussed.