Synthesis of 6-Substitutedchromone-2- Carboxamide derivatives as corrosion inhibitors for metals in acidic medium

Abstract

Corrosion is the gradual deterioration of a metal's properties as a result of its interaction with the surrounding environment. One method of controlling corrosion is to use corrosion inhibitors, substances added to a corrosive environment in trace quantities to reduce the rate of corrosion. In this study, five (5) non-toxic and inexpensive 6-substitutedchromone-2-carboxamides derivatives (Chromone-2-carboxamide, 6-bromochromone-2-carboxamide, 6-chlorochromone-2-carboxamide, 6-methoxychromone-2-carboxamide and 6-nitrochromone-2-carboxamide) were successful synthesized and evaluated as potential corrosion inhibitors in 1.5 M HCl for mild steel (MS) and zinc (Zn), and 1.0 M HCl for aluminium (Al) using experimental and computational techniques. All these inhibitors were first synthesized and then characterized by spectroscopic methods namely: Nuclear Magnetic Resonance (NMR) spectroscopy (1H NMR and 13C NMR), Mass Spectrometry and Fourier-Transform Infrared (FTIR) spectroscopy. The corrosion inhibition potentials of the corrosion were investigated using gravimetric analysis (GA), electrochemical analysis, theoretical studies, and surface morphology studies. Results from GA on MS showed an increase in percentage inhibition efficiency (%IE) as inhibitor concentration was increased, with NO2-Chr-2-Carb showing the highest %IE (97.44%). The Langmuir adsorption isotherm was found to be the best-fit for all the corrosion inhibitors for all metal surfaces. All the synthesized compounds reduced the corrosion rate of three metals in the HCl solution. These corrosion inhibitors also exhibited mixed-type inhibitive action for the Al and MS, while physical adsorption was dominating on Zn. Spectra from FTIR showed that all corrosion inhibitors formed adsorption films on all metal surfaces, successfully inhibiting the corrosion process. Potentiodynamic Polarization (PDP) measurements revealed that these inhibitors reduced the rate of anodic and cathodic corrosion reactions, as shown by Tafel polarization measurements. Electrochemical Impedance spectroscopy (EIS) measurements revealed an increase in diameter of imperfect semicircles with increase in the concentration of inhibitors, suggesting increase in the surface coverage of adsorptive inhibitors on the metal surfaces, thus increase in charge transfer resistance. Spectroscopic studies for surface analysis by SEM/EDS and wettability contact angle technique proved that the inhibitors induced a barrier for the corrosion process and created the hydrophobic surfaces. Quantum chemical calculations confirmed the importance of heteroatoms (O and N) in corrosion inhibition and gave a clear view on how the inhibitors adsorbed on the metal surfaces.