A Comparative Study of the Oxidation of 3-, 4- and 5-Aminosalicylic Acids at Glassy Carbon Electrodes

Abstract

The oxidation behavior of 3-aminosalicylic acid (3-ASA), 4-aminosalicylic acid (4-ASA) and 5-aminosalicylic acid (5-ASA), the active part of the drugs Sulphasalazine and Dipentum for the treatment of ulcerative colitis, has been compared. The redox behavior is complicated by extensive follow-up chemistry and it is shown that the influence of the latter depends on the position of the amino group, as well as the experimental time domain and pH. For 3- and 5-ASA, the oxidation most likely gives rise to benzoquinone imines which then undergo chemical reactions to yield, e.g., the corresponding benzoquinones and after electrochemical reduction also the dihydroxybenzoic acids as intermediates. The results indicate that the rate of the chemical step is higher for 3-ASA than for 5-ASA while for 4-ASA, an electroinactive film is formed on the electrode surface most likely due to a polymerization involving the oxidation product.