The conversion of some catecholamines, such as L-dopa, dopamine and methyldopa, to their corresponding nitro-derivatives, or their oxidative degradation, in the presence of nitrous acid/nitrite ion equilibria has been studied using voltammetric techniques in aqueous solution. The results indicate that nitrous acid, as an oxidant, converts the catecholamines to their quinone derivatives and that the produced quinones are attacked by their side chain amine group or the nitrite ion. Oxidation as the first step and a competition between an intramolecular and intermolecular Michael addition as the second reactions were studied at various pH values. The homogeneous rate constants for the oxidation and Michael addition reactions were estimated by fitting through the selective current-time profiles. (C) 2009 Elsevier Ltd. All rights reserved.