Quantum Chemical Studies on the Corrosion Inhibitions of Mild Steel in Acidic Medium by 5-amino-1-cyclopropyl- 7-[(3R,5S)-3,5-dimethylpiperazin-1-yl]-6,8-difluoro-4-oxo- 1,4-dihydroquinoline-3-carboxylic acid

摘要

Experimental aspect of the corrosion inhibition of mild steel in phosphoric acid by 5-amino-1-cyclopropyl-7-[(3R,5S)- 3,5-dimethylpiperazin-1-yl]-6,8-difluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (ACA) was carried out using gravimetric, gasometric and thermometric methods while theoretical studies were carried out using quantum chemical and density functional theory (DFT) approaches. The results obtained indicated that ACA is a good adsorption inhibitor for the corrosion of mild steel in H3PO4 solutions. The adsorption of the inhibitor on mild steel surface was found to be spontaneous and was described by Temkin adsorption model. From the values of free energy of adsorption, a physical adsorption mechanism has been proposed for the adsorption. The average inhibition efficiencies correlated strongly with some quantum chemical parameters (frontier molecular orbital energies, energy gap, electronic energy of the molecule, core - core repulsion energy, dipole moment, and heat of formation) calculated. The adsorption of ACA on the metal surface would preferentially be through the N (20), O (12) and O (14).