Electrochemical oxidation of catechol 1a and 4-tert-butylcatechol 1b has been studied in the presence of 1-methyl-1H midazole-2-thiol 3 as nucleophile in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results ndicate the participation of catechol 1a and 4-tert-butylcatechol 1b in Michael reaction with 3 to form the corresponding catechol hioethers 6a and 4b. Based on the observed EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with digital simulated results.