The oxidation process induced by 2-mercaptopyrimidine (RSH) at a hanging mercury drop electrode was studied in aqueous media by normal and cyclic voltammetry. The results indicate the formation of a weakly adsorbed HgSR complex according to the reaction Hg + RSH -> HgSR + e(-) + H+. When the surface excess of HgSR is high, a two-dimensional condensation takes place if the potential is positive enough, as proved by phase-sensitive ac and cyclic voltammetry. (c) 2005 Elsevier Inc. All rights reserved.