Mechanistic Aspects on the Grafting By the Self-Decomposition of Aryldiazonium Salts: Effect of the Counterion

Abstract

The dipping of an electrode in a solution of aryldiazonium salts is an interesting reaction to form covalently grafted films on carbon and metallic surfaces [1]. However, although there are many evidences about the existence of the grafted film, the mechanism is unknown. In 1957, it was demonstrated that p-nitrofluorobenzene was got during the thermal decomposition of p-nitrophenyldiazonium tetrafluoroborate, putting in evidence the importance of the counterion during the decomposition of the aryldiazonium cation [2]. One way to explain the formation of this specie considers the decomposition of the aryldiazonium cation by a redox reaction that involves the transient passage by radicals as intermediates, which will be responsible of the spontaneous grafting of different electrode surfaces. Hence, the theoretical and experimental study for determine the mechanism of the spontaneous grafting is performed in this work. The results showed that there is an effect of the counterion in the rate of decomposition of the aryldiazonium salt. When the counterion is easier to be oxidized, the rate of decomposition is higher, which support the idea of a mechanism with a redox reaction involved and therefore, the existence of radicals as intermediates.