Experimental and computational investigation of 3,5-di-tert-butyl-2-(((3-((2-morpholinoethyl)(pyridin-2-ylmethyl) amino)propyl)imino) methyl)phenol and related reduced form as an inhibitor for C-steel

Abstract

The effect of new compounds containing morpholine moiety including: 3,5-di-tert-butyl-2-(((3-((2-morpholinoethyl)(pyridine-2-ylmethyl)amino)propyl)imino)methyl)phenol (L1) and its reduced form, 3,5-di-tert-butyl-2-(((3-((2-morpholinoethyl)(pyridine-2-ylmethyl)amino)propyl)amino) methyl)phenol (L2) on the corrosion inhibiting of C-steel in 1.0 M HCl and 3.5 wt% NaCl was tested by experimental and computational techniques. The concentration of inhibitor varied in the range of 0.2–2.0 mM. The corrosion behavior of C-steel was investigated using electrochemical techniques, including open circuit potential (OCP), potentiodynamic polarization (Tafel), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) inhibitor-free and inhibitor-containing solutions. From the Tafel diagram, the icorr of the C-steel electrode in the 1.0 M hydrochloric acid solution represents the highest value among the other inhibitor-containing solutions. The icorr for C-steel in L1 containing solution decreases gradually from 1.43 × 10−4 to 0.91 × 10−4 A/cm2, with the concentration of L1 increasing from 0.2 to 2.0 mM. Along with the increase of the L2 concentration from 0.2 to 2.0 mM, the icorr is reduced by about 41%. EIS studies demonstrated that the capacitance of the double layer increased by the addition of inhibitors and increasing the resistance of charge transfer, suggesting an improvement of the corrosion protection in inhibitor-containing acidic solution. SEM images confirmed the corrosion results in which inhibitor-containing solution protects the C-steel surface against the attack of species. The results showed that in all solutions containing equivalent concentrations of inhibitors, the reduced form of L1 had a better inhibition efficiency than the L1 inhibitor. Inhibitors, L1 and its reduced form exhibit Langmuir adsorption isotherm, in which monolayer adsorption of inhibitors is carried out on the C-steel electrode. The properties of the studied molecules to be corrosion inhibitors were examined with the Gaussian software program. The calculations of the molecules were made in different methods and basis sets.