Density Functional Theory and Quantitative Structure-Activity Relationship Studies of some Quinoxaline derivatives as potential Corrosion Inhibitors for Copper in Acidic Medium

Density Functional Theory (DFT) using the B3LYP functional and Quantitative Structure-Activity Relationship QSAR studies is reported on some quinoxaline derivatives namely 3-methyl-2-phenyl quinoxaline (MPQ), 2,3-diphenyl quinoxaline (PPQ), 3-methyl-2(2-hydroxyphenyl)quinoxaline (MHPQ), 3-phenyl-2(2-hydroxyphenyl)quinoxaline (PHPQ) and 3-methyl-2(3-methoxy,4- hydroxyphenyl)quinoxaline (MMtHPQ) used as corrosion inhibitors for copper in acidic medium. DFT was utilized to model the quinoxaline---Cu interaction mechanism in order to obtain molecular reactivity parameters (for elucidating the reactivity tendency for each of the studied quinoxaline derivative). Some of the reactivity parameters were correlated with the experimentally determined inhibition efficiencies using quantitative structure activity relationship (QSAR). The results show that an optimum of three quantum chemical parameters is sufficient to correlate with experimentally determined inhibition efficiencies. The quinoxaline---Cu interaction shows that the Cu atom binds to the quinoxaline derivatives with the preferred geometries corresponding to cases in which the Cu atom is in a multi-dentate mode or geometry.