An-Najah Staff

In the present work, a theoretical study of two quinoxaline-type organic compounds, (2Z)-2-[(3E)-3(2-oxo-2-phenylethylidene)-3, 4-dihydroquinoxalin-2(1H)-ylidene]-1 phenylethanone (Q5) and (Z)-2((E)-3-(2-oxo-2-phenylethylidene)-3, 4-dihydroquinoxalin-2(1H)-ylidene)-1-phenylethanone (Q6), has been performed using density functional theory (DFT) at the B3LYP/6-31G(d) level in order to elucidate the different inhibition efficiencies and reactive sites of these compounds as corrosion inhibitors. The efficiencies of corrosion inhibitors and the global chemical reactivity relate to some parameters, such as highest occupied molecular orbital energy (E ), lowest unoccupied molecular orbital energy (E LUMO HOMO ), energy gap (ΔE), dipole moment (µ), electronegativity (χ), electron affinity (A), global hardness (η), softness (s), ionization potential (I), the fraction of electrons transferred (∆N), the global electrophilicity (ω) and the total energy (TE), were calculated. All calculation has been performed by considering Density Functional Theory (DFT) using the GAUSSIAN03W suite of programs. The calculated results are in agreement with the experimental data on the whole.

2Z)-1-(4-chlorophenyl)-2-[(3E)-3-[2-(4-chloropheny l)-2-oxoethylidene]-3,4dihydro quinoxalin- 2 (1H)-ylidene]ethanone (Q4) was tested as inhibito r for the corrosion of copper in 2M HNO 3 using gravimetric method at 303 – 343 K. The inhibi tor (Q4) showed about 90% inhibition efficiency (E (%)) at an optimum concentration of 1 0 -3 M. The inhibition efficiency increases with increase in inhibitor concentration but decrease wi th rise in temperature. Various parameters (Ea , ∆G ° ads , K ads ) for adsorption reveal a strong interaction betwee n inhibitor and copper surface. The negative values of ∆G° ads indicate the spontaneous adsorption of the inhibit or on copper surface. Kinetic parameters activation such as a E , aH °∆ , aS °∆ and pre-exponential factor have been calculated and discussed. Further, theore tical calculations were carried out and relations between computed parameters and experimen tal inhibition efficiency were discussed.

N-1-Naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME) was tested as a corrosion inhibitor for copper in 2 M HNO3 solution using the standard gravimetric technique at 303–343 K. N-NEDHME acts as an inhibitor for copper in an acidic medium. Inhibition efficiency increases with increase in concentration of N-NEDHME but decreases with a rise in temperature. Thermodynamic parameters such as adsorption heat ( \UpdeltaH∘ads ), adsorption entropy ( \UpdeltaS∘ads ) and adsorption free energy (\UpdeltaG∘ads) were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 303 to 343 K. Kinetic parameters activation such as Ea , \UpdeltaH∘a , \UpdeltaS∘a and pre-exponential factors have been calculated and are discussed. Adsorption of N-NEDHME on the copper surface in 2 M HNO3 follows the Langmuir isotherm model.

The inhibition of the corrosion of copper in 2M HNO3 by 5-[hydroxy(phenyl)methyl]-6 methylpyridazin-3 (2.6 )-one (P1), 4-(2-chlorobenzyl)-6-hydrazino-3-methyl-1,6-dihydropyridazine (P2), 5-(2,6-dichlorobenzyl) -6-methylpyridazin-3(2H)-one (P3) and 5-[(2chlorophenyl) (hydroxy)methyl]-6-methylpyridazin-3(2H)-one (P4) has been investigated at 303K using weight loss measurements, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) methods). Results obtained show that P3 and P4 are the best inhibitors and their inhibition efficiencies (E %) increase with the increase of inhibitor concentration and reach up to 96 and 94 % for P3 and P4 at 10-3 M, respectively. Moreover, polarisation studies clearly reveal that the presence of inhibitors changes the mechanism of hydrogen evolution and that they act as mixed inhibitors. EIS study shows that charge transfer resistance increases with the inhibitor concentration. The adsorption of P3 obeys to the Langmuir isotherm. The activation parameters of copper in the presence and absence of P3 are also evaluated and discussed. Effect of temperature is studied between 298 and 353 K and determination of activation parameters is also discussed in part 2. Explanation by quantum indices to correlate inhibition efficiency should be given in part 3.

The efficiency of 1H-1,2,4-triazol-3-amine (Tz1), 4-amino-3-hydrazino-4H-1,2,4-triazole-3-thiol (Tz2), and 1H-1,2,4-triazole-3,5-diamine (Tz3) as inhibitors of corrosion of copper in nitric acid was investigated by use of density functional theory (DFT). Quantum chemical data, for example energy of the highest occupied molecular orbital (E HOMO), energy of the lowest unoccupied molecular orbital (E LUMO), energy gap (ΔE), dipole moment (μ), electronegativity (χ), electron affinity (A), global hardness (η), softness (σ), ionization potential (I), fraction of electrons transferred from the inhibitor molecules to the metallic atom (ΔN), and total energy (TE), were calculated. All calculations were performed by use of DFT with Gaussian 03W software. A good correlation was found between theoretical data and experimental results.