Estimation of Heterogeneous Rate Constants of Reaction of Electrochemically Generated o-Benzoquinones with Various Nucleophiles Containing Thiol Group

The reaction of o-benzoquinone derived by the oxidation of catechols (I a-c) with some nucleophiles containing thiol group (2a-f) has been studied in various conditions, such as pH, nucleophile concentration, and scan rate, using cyclic voltammetry. In various conditions, based on an EC electrochemical mechanism (E represents an electron transfer at the electrode surface and C represents a homogeneous chemical reaction), the observed homogeneous rate constants (k(obs)) were estimated by comparison of the experimental cyclic voltammetric responses with the digital simulated results for each of the nucleophile. The results show that the magnitude of k(obs) is dependent on the nature of the substituted group on the catechol ring and nucleophilicity of nucleophile. (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 426-431, 2009