Isolation, Characterisation and Corrosion Inhibition Evaluation of 1, 3, 5-Trimethoxymethylbenzenefrom Seeds Extract of Cola nitida on Mild Steel Surface in Hyhrochloric Acid Solution

Corrosion inhibition of Mild steel in 1 M hydrochloric acid solution by 1, 3, 5-trimethoxymethylbenzene (TMMB) isolated from seeds extract of Cola nitida was studied using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic methods. TMMB was isolated from seeds of C. nitida by 72 hours maceration of the chopped seeds with dichloromethane. Filtered and concentrated extract was subjected to a combination of vacuum liquid, column and thin layer chromatographic techniques. The isolated compound was characterized using Fourier Transform Infra-Red (FT-IR) spectrophotometer, proton nuclear magnetic resonance (+H-NMR), C13 – NMR and DEPT-135 NMR spectrophotmeters. The results showed that the inhibition efficiency recorded by the weight loss method increased with the increase in TMMB concentration, but decreased with increasing temperature. The inhibition efficiencies recorded by the potentiodynamic polarization and electrochemical impedance spectroscopic methods also increased with increase in the concentration of TMMB. The calculated thermodynamic parameters showed that the corrosion inhibition process was endothermic and spontaneous in nature. Potentiodynamic polarization measurements confirmed that TMMB worked as a mixed – type inhibitor considering the value of Ecorrbeing less than 85 mV. Impedance measurement revealed that the charge transfer resistance offered by TMMB to the migration of aggressive ions on the surface of mild steel in acidic solution was enough to impede corrosion. The best line of fit to the adsorption of TMMB onto mild steel surface was found in Temkin isotherm. Formation of protective dense film on the steel surface in the presence of TMMB compared to the blank was revealed by scanning electron microscopy. The molecular structure of TMMB was optimized using Gausian 09 with density functional theory [DFT/B3LYP/6-31G (d,p)]. Physical adsorption has been proposed for the adsorption of TMMB onto mild steel surface.