Synthesis, characterization and evaluation of the corrosion inhibition on mild steel of two new Schiff bases derived from 4,4'-diaminobiphenyl: Density functional theory investigation

Abstract

The present work deals with the synthesis of two new heterocyclic Schiff bases, namely 4,4’-bis(3-thienylideneimino) biphenyl (HL1) and 4,4’-bis(2-furylideneimino) biphenyl (HL2), by condensing 4,4'-diaminobiphenyl with 3-carboxaldehyde thiophene and 2-carbaxaldehyde furan, respectively. The obtained compounds were characterized by different spectroscopic techniques. The corrosion inhibition properties of the investigated Schiff bases were evaluated for mild steel in 1M HCl medium, using weight loss measurement, potentiodynamic polarization and impedance spectroscopy. All the measurements showed that the inhibition efficiency increases with the increase in the inhibitor’s concentrations. Furthermore, the experimental results were confirmed by the quantum chemical calculations using the density functional theory (DFT). The different proprieties for each compound have been analyzed by means of the HOMO-LUMO to determine the energy gap (∆E), Electron affinity (EA), Ionization potential (I), Global Electrophilicity (ω), Global Hardness (η) and Chemical Potential (µ). The fraction of electrons transferred (ΔN) and the total energy (TE) were also calculated. The local selectivity and reactivity have been analyzed through the Fukui function in order to compare the possible sites for nucleophilic and electrophilic attacks. The polarization curves studies showed that both tested compounds are mixed-type inhibitors. The DFT investigation is in good accordance with the experimental results.