Spontaneous derivatization of a copper electrode with in situ generated diazonium cations in aprotic and aqueous media

Spontaneous derivatization of copper electrode surfaces with 4-nitrophenyl groups from the corresponding diazonium cations, in situ generated, in aprotic (0.1 M NEt4BF4 in ACN) and aqueous acidic (0.1 M CH3COOH) medium is described. The 4-nitrophenyl diazonium cations were synthesized in the electrochemical cell by reaction of 4-nitroaniline with tert-butyl nitrite in aprotic media and with NaNO2 in aqueous media. Derivatized copper electrode surfaces were characterized by cyclic voltammetry, Fourier transform infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. The main finding of this study was the spontaneous formation of multilayered coating in aprotic media and the spontaneous formation of close to a monolayer coating in aqueous acid media. The effect of the experimental conditions leading to the formation of the grafted layer in aqueous acidic media was also investigated. The limitations of the approach involving in situ generated diazonium cations relative to that making use of a diazonium salt are also presented.