Interaction of Two Water Soluble Heterocyclic Hydrazones on Copper in Nitric Acid: Electrochemical, Surface Morphological, and Quantum Chemical Investigations

Two novel heterocyclic compounds (E)-2-(1-(pyridin-3-yl)ethylidene)hydrazinecarbothioamide (3APTSC) and (E)-3-(1-(2-phenylhydrazono)ethyl)pyridine (3APPH) derived from 1-(pyridin-3-yl)ethanone were synthesized and characterized by various spectroscopic techniques. The corrosion inhibition efficacies of these compounds on copper in 0.1 M HNO3 were screened by electrochemical corrosion monitoring techniques such as potentiodynamic polarization studies and impedance spectroscopy. Investigations clearly established that 3APPH displayed higher corrosion inhibition efficiency on Cu than 3APTSC at all concentrations. The mechanism of inhibition was verified with the help of adsorption isotherms. 3APTSC and 3APPH obeyed Langmuir adsorption isotherm on Cu surface. Thermodynamic parameters such as adsorption equilibrium constant (Kads) and free energy of adsorption (ΔGads) were also evaluated. Potentiodynamic polarization investigations confirmed that the 3APTSC and 3APPH act as mixed type inhibitors. Surface analysis of the metal specimens was performed by scanning electron microscopy. Energy of HOMO and LUMO, their difference, number of electrons transferred, electronegativity, chemical hardness, and so forth were evaluated by quantum chemical studies. Agreeable correlation was observed between the results of quantum chemical calculations and other corrosion monitoring techniques.