Electrochemical oxidation of ortho- and para-aminophenol derivatives (2-aminophenol, 2-methylaminophenol, 4-aminophenol, 4-methylaminophenol and acetaminophen) has been studied in acidic solutions by means of cyclic voltammetry and controlled-potential coulometry. The results indicated that the oxidation forms of para-aminophenols undergo hydrolysis by formation of p-benzoquinone as final product and the oxidation of ortho-aminophenol derivatives is accompanied by dimerization reaction. The effect of different parameters such as substitute effect, pH, aminophenol concentration and time window of chosen electrochemical method has been discussed on the reaction rate of dimerization and hydrolysis. The hydrolysis and dimerization reaction rates are completely dependent on the substituted group linked to N atom and position of amine group in the molecule. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.043301jes] All rights reserved.