Ahmed Y. Musa

The Antioxidant Activity of New Coumarin Derivatives

The antioxidant activity of two synthesized coumarins namely, N-(4,7-dioxo-2- phenyl-1,3-oxazepin-3(2H,4H,7H)-yl)-2-(2-oxo-2H-chromen-4-yloxy)acetamide 5 and N-(4-oxo-2-phenylthiazolidin-3-yl)-2-(2-oxo-2H-chromen-4-yloxy)acetamide 6 were studied with the DPPH, hydrogen peroxide and nitric oxide radical methods and compared with the known antioxidant ascorbic acid. Compounds 5 and 6 were synthesized in a good yield from the addition reaction of maleic anhydride or mercaptoacetic acid to compound 4, namely N′-benzylidene-2-(2-oxo-2H-chromen-4-yloxy)acetohydrazide. Compound 4 was synthesized by the condensation of compound 3, namely 2-(2-oxo-2H-chromen-4-yloxy) acetohydrazide, with benzaldehyde. Compound 3, however, was synthesized from the addition of hydrazine to compound 2, namely ethyl 2-(2-oxo-2H-chromen-4-yloxy)acetate, which was synthesized from the reaction of ethyl bromoacetate with 4-hydroxycoumarin 1. Structures for the synthesized coumarins 2–6 are proposed on the basis of spectroscopic evidence.

The Use of Umbelliferone in the Synthesis of New Heterocyclic Compounds

New coumarin derivatives, namely 7-[(5-amino-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one (4), 5-[(2-oxo-2H-chromen-7-yloxy)methyl]-1,3,4-thiadiazol-2(3H)-one (5), 2-[2-(2-oxo-2H-chromen-7-yloxy)acetyl]-N-phenylhydrazinecarbothioamide (7), 7-[(5-(phenylamino)-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one (8) and 7-[(5-mercapto-4-phenyl-4H-1,2,4-triazol-3-yl)methoxy]-2H-chromen-2-one (9) were prepared starting from the natural compound umbelliferone (1). The newly synthesized compounds were characterized by elemental analysis and spectral studies (IR, 1H-NMR and 13C-NMR).

Inhibition of Mild Steel Corrosion in Hydrochloric Acid Solution by New Coumarin

A new coumarin derivative, N,N′-((2E,2′E)-2,2′-(1,4-phenylenebis(methanylylidene))bis(hydrazinecarbonothioyl))bis(2-oxo-2H-chromene-3-carboxamide) PMBH, was synthesized and its chemical structure was elucidated and confirmed using spectroscopic techniques (Infrared spectroscopy IR, Proton nuclear magnetic resonance, 1H-NMR and carbon-13 nuclear magnetic resonance 13C-NMR). The corrosion inhibition effect of PMBH on mild steel in 1.0 M HCl was investigated using corrosion potential (ECORR), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) measurements. The obtained results indicated that PMBH has promising inhibitive effects on the corrosion of mild steel in 1.0 M HCl across all of the conditions examined. Scanning electron microscopy (SEM) was used to investigate the morphology of the mild steel before and after immersion in 1.0 M HCl solution containing 0.5 mM of PMBH. Surface analysis revealed improvement of corrosion resistance in presence of PMBH.

Electrochemical Study on Newly Synthesized Chlorocurcumin as an Inhibitor for Mild Steel Corrosion in Hydrochloric Acid

A new curcumin derivative, i.e., (1E,4Z,6E)-5-chloro-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,4,6-trien-3-one (chlorocurcumin), was prepared starting with the natural compound curcumin. The newly synthesized compound was characterized by elemental analysis and spectral studies (IR, 1H-NMR and 13C-NMR). The corrosion inhibition of mild steel in 1 M HCl by chlorocurcumin has been studied using potentiodynamic polarization (PDP) measurements and electrochemical impedance spectroscopy (EIS). The inhibition efficiency increases with the concentration of the inhibitor but decreases with increases in temperature. The potentiodynamic polarization reveals that chlorocurcumin is a mixed-type inhibitor. The kinetic parameters for mild steel corrosion were determined and discussed.

Corrosion inhibitive property of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol for mild steel corrosion in 1·0M hydrochloric acid

Abstract The efficiency of 4-Amino-5-phenyl-4H-1,2,4-triazole-3-thiol (APTT) as corrosion inhibitor for mild steel metal in 1·0M HCl has been investigated. Weight loss, direct current (potentiodynamic polarisation), alternating current (electrochemical impedance spectroscopy), change of open circuit potential (OCP) with immersion time and scanning electronic microscopy were used to study the effect of APTT on the corrosion inhibition of mild steel. Results obtained from weight loss, potentiodynamic polarisation, impedance measurements and change of OCP with immersion time are in good agreement and indicated that the inhibitive efficiency of the inhibitor increases with the rise of concentration. Polarisation curves show that APTT is a mixed type inhibitor. Results showed that APTT performed excellent inhibiting effect for the corrosion of mild steel in 1·0M HCl solution and inhibition efficiency is higher than 90% at 80 × 10–5 M APTT. The high inhibition efficiency in terms of molecular adsorption and forming a protective film on the metal surface was discussed in this work. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm and the value of the free energy of adsorption ΔG ads indicated that the adsorption of APTT molecule was a spontaneous process and was typical of chemisorptions. Surface photographs showed a good surface coverage on the metal surface.

Synergistic of a coumarin derivative with potassium iodide on the corrosion inhibition of aluminum alloy in 1.0 M H2SO4

Synergistic effects of the addition of KI on the corrosion inhibitive performance of a coumarin derivative on an aluminum alloy in 1.0 M H2SO4 at different temperatures were studied using various electrochemical measurements. Density functional theory was used to calculate the quantum chemical parameters of the coumarin derivative. The experimental results showed that the coumarin derivative is considered as a mixedtype inhibitor. The corrosion potential values were almost unchanged upon the addition of PBBC to the acidic solution. The inhibition efficiency increases with increasing inhibitor concentration and increases further in the presence of 6.02 mM KI but decreases significantly at higher temperature. The adsorption of PBBC obeyed the Langmuir isotherm, and being chemically adsorbed at lower temperatures, while physical adsorption is favoured at higher temperature. The theoretical results indicated that the coumarin derivative was adsorbed onto the surface of Al2024 through the sulfur, oxygen and nitrogen atoms.

The role of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol in the inhibition of nickel–aluminum bronze alloy corrosion: electrochemical and DFT studies

Inhibition of corrosion of nickel–aluminum bronze alloy (NAB) by use of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol (APTT) was investigated by monitoring weight loss and open-circuit potentials (OCP), and by use of electrochemical impedance spectroscopy (EIS). Quantum chemical data were calculated by use of the density functional theory (DFT) model. Results showed that APTT inhibits corrosion of NAB alloy fairly well. The efficiency of inhibition increases with increasing concentration of APTT, and adsorption of the inhibitor obeys the Langmuir adsorption isotherm model. Negative values of adsorption free energy indicate chemical adsorption is spontaneous. The theoretical study showed that sulfur and nitrogen atoms (S, N7 and N8) were the reactive sites.

Galvanic corrosion of aluminum alloy (Al2024) and copper in 1.0M hydrochloric acid solution

The corrosion of an aluminum alloy (Al2024) and copper in 1.0M HCl solution was investigated at 30, 40, 50 and 60 °C using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements. The galvanic corrosion of Al2024 and copper was studied using the zero resistance ammeter (ZRA) method. Galvanic current densities (Ig) and galvanic potential (Eg) were measured at 30 °C in 1.0M HCl solution. Thermodynamic parameters, such as activation energy (Ea), enthalpy of activation (ΔHa) and entropy of activation (ΔSa), were calculated and discussed. The results indicated that the corrosion rates of both Al2024 and copper increased with temperature. The ZRA results demonstrated that Al2024 is a sacrificial anode in 1.0M HCl solution when coupled with copper.

Quantum chemical calculation for the inhibitory effect of compounds

The effects of the molecular structure on the corrosion inhibition efficiency are investigated by nine methods of calculations. The selected thio compounds were previously identified as corrosion inhibitors for mild steel in the 1.0 M HCl solution. The electronic properties such as highest occupied molecular orbital (EHOMO) energy, lowest unoccupied molecular orbital (ELUMO) energy, dipole moment (μ), and Fukui indices are calculated and discussed. Results show that the corrosion inhibition efficiency increase with the increase in both EHOMO and μ values, respectively, and decrease in ELUMO. QSAR approach is utilized in this study; a good relationship is found between the experimental corrosion inhibition efficiency (IEexp, %) and the theoretical corrosion inhibition efficiency (IEtheor, %). The calculated inhibition efficiency is found closer to the experimental inhibition efficiency with a coefficient of correlation (R2) of 0.875.

Inhibition of galvanic corrosion by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol

Inhibition of galvanic corrosion was carried out using 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT) as corrosion inhibitor. The couple metals were aluminium alloy (Al2024) and mild steel. The galvanic potential and the galvanic current were measured in absence and presence of 0.4 mM of APTT. FT-IR was used to characterise the adsorbed inhibitor film technique. The result showed that the galvanic current was reduced from 286 to 8.9 μA cm–2 with addition of APTT. FTIR result confirmed the adsorption of APTT on mild steel surface.