Inhibition of cooper and zinc dissolution with 5(6)-nitrobenzoimidazoles in phosphate electrolytes

Effects of the concentration and chemical structures of 2-substituted 5(6)-nitrobenzoimidazoles (5(6)-NO2-2-R-BIs) on the dissolution of copper and zinc in phosphate electrolytes were studied. Introduction of the nitro group into benzoimidazole derivatives was found to make them more effective for copper but less effective for zinc; this is due to an increased degree of dissociation of the nitro derivatives and the possibility of ionic bonding in their complexes. The protective effects of 5(6)-NO2-2-R-BIs on copper and zinc depend on their chemical structures and are accurately described by the equation log γ = α ± ρσ1. The sign and magnitude of ρ indicate that electron-withdrawing substituents in 5(6)-NO2-2-R-BIs enhance the protection of copper, while electron-donating ones enhance the protection of zinc; this is due to different abilities of these metals to form σ-and π-bonds in their complexes.