Cathodic immobilization of tertiary C―H moieties onto glassy carbon via secondary alkyl halides. A versatile way for surface modification

Abstract

The complex structure of glassy carbon is exploited by means of its powerful reacting abilities under cathodic charge in aprotic solvents at quite negative potentials. Under polarization, the preliminary stage corresponds to the formation of nucleophilic centers (by reduction of graphitized and/or fullerenized) dispersed at (or in the vicinity of) the surface of such polarized materials. In the presence of electrophilic organic species such as organic halides, surface modification(s) may be obtained. These processes are expected to correspond to nucleophilic substitution (SN). While primary alkyl halides were reported to be easily fixed onto carbon in common polar aprotic solvents, secondary (and tertiary) alkyl halides were noticed to be not reactive under such conditions. Contrariwise, aprotic solvents with high dielectric constant (like propylene carbonate) permit to boost the interfacial reactivity of those halides. Thus, secondary bromides and iodides lead to compact deposits possessing tertiary protons identified by a two-electron oxidation step at about +1.2V vs. Ag/AgCl. Specifically, 2-bromoadamantane yields an organic layer assigned to grafted 2-adamantyl moiety. The chemical versatility of such deposits is presented.