Synthesis of ethylene bis [(2-hydroxy-5,1,3-phenylene) bis methylene] tetraphosphonic acid and their anticorrosive effect on carbon steel in 3%NaCl solution

The inhibition performance of the newly synthesized Ethylene bis [(2-hydroxy-5,1,3-phenylene) bis methylene] tetraphosphonic acid (ETPA) toward carbon steel in 3% NaCl was investigated at different concentrations using potentiodynamic polarization (PDP) and impedance spectroscopy (EIS) methods. It was found that the inhibition capability was increased with increasing inhibitor dose and reach 92% at 10−3 mol/L. Also, Polarization curves showed that ETPA acts as a mixed type inhibitor with predominantly control of anodic reaction. The new inhibitor was investigated by different spectroscopic methods such as 1H, 13C and 31PNMR. The quantum parameters such as absolute electronegativity (χ), energy gap ΔE (EHOMO-ELUMO), global softness (σ), global hardness (η), electrophilicity index (ω) and the number of transfer electrons (ΔN) are calculated by density functional theory (DFT). The experimental also correlated with density functional theory results. The calculations show that ETPA has high density of negative charge located on the oxygen atoms of the phosphonate group facilitating the adsorption of ETPA on the surface of carbon steel. The inhibition efficiency of ETPA was discussed in terms of blocking of electrode surface by adsorption of ETPA molecules through active centers. The adsorption of ETPA on the surface of carbon steel obeyed the Langmuir isotherm paradigm.