Radical grafting of carbon surfaces with alkylic groups by mediated oxidation of carboxylates

The mediated oxidation of tetrabutylammonium acetate and 4-nitrophenylacetate was carried out in acetonitrile on glassy carbon electrodes. It is discussed that direct oxidation of aliphatic carboxylates, which give rise to a carbocationic chemistry, cannot induce covalent grafting of the carbon surface, however surface grafting is possible by using ferrocene derivatives as electron transfer mediators. Density functional theory has been used to model a radical grafting involving methyl groups. In addition semiempirical calculations have been performed for 4-nitrobenzyl additions, and a new anchoring pattern, is proposed. Coverage factors have been calculated for both kinds of radicals. Both, experimental and theoretical results support the covalent attachment of methyl groups on the carbon surface and the formation of a highly compact monolayer which does not allow the permeation of reversible redox molecules as small as the molecular oxygen.