Electrochemical oxidation of catechols (1a-e) has been studied in the presence of sulfite ion (3) as nucleophile in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of catechols (1a-e) in Michael reaction with 3 to form the corresponding sulphonated derivatives. Based on ECE, ECEC or ECECEC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results