SILVA, ELAINE F. ; WYSARD, JULIO S. ; BANDEIRA, MERLIN C.E. ; Mattos, Oscar R. ; ALVES, WAGNER A. .
Resumo: Surface enhanced raman scattering (SERS) spectra of 4‐methylimidazole (4‐MeImid) are shown for the first time on a copper electrode and in the presence of chloride. The potential dependence on the spectra reveals that the N1H tautomer is majority close to the open circuit, but the N3H tautomer predominates at more cathodic polarizations. At these latter conditions, 4‐MeImid orientation changes from tilted to perpendicular, and such a behavior is similar to the one of Imid at natural pH. Interesting issues are observed at pH = 2.0: (a) 4‐MeImidH+ is not identified on the metal surface for the whole applied potential range and must be either adsorbed as an ion pair with chloride or in the bulk solution; (b) at open circuit and anodic polarization, its neutral form is the unique azole species present, in contrast to the ImidH+ behavior, which is easily observed in the surface spectra. SERS spectra of 4‐methylimidazole (1) and its cation (2), on a copper electrode, are presented for the first time in the literature as well as the classic equilibrium involving the neutral tautomers, which has been only observed in solution. The data support electrochemical results reported by other authors about the better copper corrosion inhibition efficiency of (1) as compared with imidazole at acidic media.
