Effects of Substituted Benzotriazoles on the Electrochemical Behavior of Copper in H₂SO₄

Rates of anodic dissolution of copper as well as hydrogen evolution in H₂SO₄ containing substituted benzotriazoles have been examined. The aromatic ring-substituted benzotriazoles studied were: 5-NH₂, 5-NO₂, 5-CH₃, 5-Cl, 5-COOH, a mixture of 4-COOH and 5-COOH, and the unsubstituted benzotriazole (BTA). The anodic polarization results indicate that BTA-NH₂, BTA-COOH and BTA-Cl inhibit copper electrodissolution by surface blockage, with the bare copper surface oxidizing to Cu(II) as the uninhibited metal. In the presence of the other benzotriazoles, copper apparently oxidizes to Cu(I) by forming slightly soluble organo-Cu(I) complexes as the oxidation product. As reported previously by others, copper electrooxidizes to cuprous chloride complexes in the presence of chloride ions (0.1 M). None of the benzotriazoles had any effect on the anodic dissolution of copper in the acidic chloride solutions below zero volts vs SCE. On the other hand, at higher potentials where a current plateau was obtained, as reported previously by others, significant differences in the position of the current plateau were observed by addition of the substituted benzotriazoles.