Methyl Substitution in Benzotriazole and Its Influence on Surface Structure and Corrosion Inhibition

Fourier transform infrared reflection absorption spectroscopy (FT‐IRAS) and polarization resistance measurements have been used to investigate the surface structure and inhibiting properties of all four monosubstituted methylbenzotriazoles on copper surfaces. The formation of a protective barrier layer is strongly dependent on the position of the methyl group in the benzotriazole (BTA) molecule as well as on the presence of a cuprous oxide on the copper surface. Substitution of a methyl group in the triazole ring, 1Me‐ or 2Me‐BTA, prevents the formation of a protective layer on the surface, whereas introduction of a methyl group in the benzene ring, 4Me‐ and 5Me‐BTA results in the formation of stable layers, 30 and 70Å, respectively. The inhibiting efficiencies for 4Me‐ and 5Me‐BTA are even higher than for BTA itself. It is concluded from a comparison with BTA that other parameters than film thickness and surface orientation must be taken into account in order to explain the differences in inhibiting properties. The increased hydrophobic character of the methyl substituted BTA derivatives may explain their superior inhibiting efficiencies in relation to BTA.