Gravimetric analysis and quantum chemical assessment of 4-aminoantipyrine derivatives as corrosion inhibitors

Organic molecules containing phosphorous, sulphur, oxygen, and nitrogen atoms are recognized substances that prevent steels from corroding in corrosive media. It is believed that organic compounds can stop corrosion by adhering to metallic surfaces. Similar factors include aromaticity, steric characteristics, electron density at donor sites, electronic structure of inhibitory compounds, and the presence of functional groups such -C=N-, -N=N-, -C = N, etc. In addition, the area and molecular weight of the molecule and the electrochemical potential at the steel/environment contact all affect adsorption. In the current study, experimental and theoretical investigations of two 4-aminoantipyrine-type Schiff bases, N-(2-nitrobenzylidene)4-antipyrinamine (2-NAA) and N-(4-nitrobenzylidene)-4-antipyrinamine (4-NAA), were conducted using gravimetric analysis and quantum chemical assessment using the density functional theory (DFT). 2-NAA and 4-NAA were studied by mass loss techniques as mild steel corrosion inhibitors in 1 M HCl solutions. The inhibitive efficiencies touch the heights at 0.5 mM, giving 95.03 and 91.88% for 2-NAA and 4-NAA, respectively. The decrease in the corrosion rate (CR) and the increase in the inhibition efficiency (IE%) in the presence of the examined inhibitors are due to the formation of a protective layer, which is adsorbed on the mild steel surface in place of the water and chloride ions which existed already. Both 2-NAA and 4-NAA adsorption isotherms obey Langmuir adsorption modes. The decrease in inhibition efficiency for both inhibitors with an increase in temperature indicates a physisorption mechanism, although chemical adsorption takes a part. These facts were confirmed according to the free energy values. Several parameters, including frontier molecular orbitals (HOMO and LUMO), energy gap (Delta E), electronegativity (chi), dipole moment (mu), electron affinity (A), softness (sigma), hardness (eta), ionization potential (I), and the fraction of electrons transferred (Delta N), were assessed to clarify the various inhibitive efficacies and reactive sites of 2-NAA and 4-NAA. The experimental data and the DFT conclusions are in good agreement.