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The present work deals with the synthesis of two new heterocyclic Schiff bases, namely 4,4'-bis(3-thienylidéneimino) biphenyl (HL1) and 4,4'-bis(2-furylidéneimino) 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. [ABSTRACT FROM AUTHOR]

An examination was conducted on a newly developed compound named N1-(coumarin-7-yl) amidrazone (Azo-Cum) to assess its impact on the corrosion of mild steel (MS) in a 1 M hydrochloric acid (HCl) solution. Various analytical techniques, including weight loss, potentiodynamic polarization (PDP), impedance spectroscopy (EIS), cyclic voltammetry (CV), UV–visible spectroscopy, scanning electron microscopy (SEM), and AFM, were employed to evaluate the inhibitory efficiency of the compound. The findings indicated that inhibition efficiency rose with higher concentrations but decreased with elevated temperatures. According to weight loss analysis, the optimal concentration of the new eco-friendly inhibitor (5 ×10−4 M) exhibited a maximum efficiency of 89.26%. Polarization studies disclosed that Azo-Cum acted as a mixed-type inhibitor with a cathodic predominance. The adsorption of the inhibitor on the MS surface followed the Langmuir adsorption isotherm. Additionally, the study explored the synergistic effect of Azo-Cum in combination with KI on MS corrosion in a 1 M HCl (Blank) solution using potentiodynamic polarization measurements. The results identified concentration ranges that demonstrated antagonistic inhibition. Density functional theory (DFT) and molecular dynamic simulation (MD) calculations were performed to investigate the correlation between molecular and chemical reactivity. • Azo-Cum inhibits corrosion in acidic environments. • Enhanced protection with Azo-Cum at optimal concentrations. • Protonated Azo-Cum shows superior inhibition. • Molecular dynamics simulation supports adsorption. • Azo-Cum forms a protective film on mild steel. [ABSTRACT FROM AUTHOR]

The corrosion inhibition effect of di[(4-phenylimino)-4-diethyl salicylaldehyde] ether (L1) and di[(4-phenylimino)-2,6-diacetyl pyridine] ether (L2) as Schiff bases on carbon steel X48 in 1 M HCl were examined with gravimetric measurement, Tafel polarization and electrochemical impedance spectroscopy (EIS). It was observed that the two compounds L1 and L2 act as greatly corrosion inhibitors. The potentiodynamic polarization results indicate that they act as anodic and cathodic type. The adsorption of each inhibitor on the mild steel surface obeys Langmuir isotherm. The associated activation parameters together with the thermodynamic data are evaluated and discussed. The characterization of the adsorbed molecules (L1 and L2) formed on the metal surface was carried out by SEM and AFM. The improvement in corrosion resistance was related to the presence of different substituent groups, apparently due to the easiness of the electron acceptance as confirmed by the quantum chemical calculations. Additionally, the molecular dynamic simulations were used to clarify the inhibition mechanism, especially, the adsorption modes and configurations of the studied inhibitor molecules. [ABSTRACT FROM AUTHOR]

• Two New Schiff bases were synthesized from 4, 4′-diaminobiphenyl with the 3-carboxaldehyde thiophene and the déhydroacitic acid. • The obtained compounds have been characterized by different physico-chemical and spectroscopic techniques. • The corrosion inhibition properties of the investigated Schiff bases were evaluated for mild steel corrosion in 1M HCl. • DFT calculations were used to correlate the experimental and theoretical parameters. • The reactivity of the molecules was interpreted from the quantum chemical calculations. In this study, two Schiff bases named (E,E)-N,N'-biphenyl-4–4′diylbis[1-(thiophen-3-yl)methanimine] (BT) and 3- [(Z)-N(4′- aminobiphenyl -4 yl) ethanimidoyl ]-2-hydroy-6-methyl-4H-pyran-4-one (BD) have been synthesized and characterized using spectroscopic techniques. The XRD technique was employed to study the atomic packing, crystal structure and space group of the developed crystals of BD. The corrosion inhibition performance of BT and BD was investigated for mild steel corrosion in 1 M HCl medium using weight loss method and electrochemical techniques. Density functional theory (DFT) and molecular dynamics (MD) simulations were further applied to explain the adsorption as well as inhibition abilities of the molecules on the mild steel surface. Compounds revealed a good inhibition action in tested medium even at low concentrations and the inhibition efficiency increases with increasing concentration of inhibitors, and revealing a mixed-type inhibitor of predominantly anodic type. SEM and EDX studies revealed the film-forming ability of the molecules on the mild steel surface. DFT and MD studies complement experimental results and demonstrate that Schiff base moieties and functional groups are responsible for corrosion inhibitive performances of studied compounds. [ABSTRACT FROM AUTHOR]