Application of Density Functional Theory to Study the Anticorrosive Effects of Some Pyrazole Derivatives

This chapter focuses on the investigation of the inhibition performances of 4-phenylazopyrazolo-3,5-diamine (L1) and six of its derivatives, namely, 4-(2-methylphenylazo)pyrazolo-3,5-diamine (L2), 4-(3-methylphenylazo) pyrazolo-3,5-diamine (L3), 4-(4-methylphenylazo)pyrazolo-3,5-diamine, (L4), 4-(2-methoxyphenylazo)pyrazolo-3,5-diamine (L5), 4-(3-methoxyphenylazo)pyrazolo-3,5-diamine (L6), and 4-(4-methoxyphenylazo)pyrazolo3,5-diamine (L7) on the corrosion of mild steel surface in nonprotonated and protonated solution. In this study, Density Functional Theory method was performed to calculate the global reactivity descriptors such as E HOMO, E LUMO, ionization energy (I), electron affinity (A), HOMO−LUMO energy gap (∆E gap), hardness (η), electrophilicity (ω), nucleophilicity (ε), softness (σ), chemical potential (µ), electronegativity (χ), the fraction of electron transferred (∆N), the initial molecule–metal interaction energy (∆ψ), and electronic back-donation energy (∆E b-d), as well as local reactivity descriptors like Fukui indices, local softness, local electrophilicity, and dual descriptors were considered and discussed. The results revealed that the most anticorrosive effect is the L7 derivative while the least one is the parent pyrazole. The type of substituent 108group and its position on the phenyl ring are also discussed. Furthermore, the examined pyrazoles showed significantly improved steel corrosion resistance, which provides opportunities to explore the inhibitive activity of structurally similar compounds.