Voltammetric properties of olsalazine sodium and some related compounds

Abstract: The voltammetric properties of Olsalazine sodium, seven other azosalicylic acids and the azoxy analogue of Olsalazine sodium have been studied in aqueous solutions mainly by cyclic voltammetry and constant potential coulometry. It was found that these compounds can all be both reduced and oxidised at a glassy carbon electrode. The reduction and oxidation potentials of the compounds were dependent on the pH and the structure of the compounds. All compounds, except 4,4'-azobis-(2-hydroxybenzoic acid), were reduced to the corresponding amino salicylic acids in a 4 e-, 4 H+ reaction, as shown by spectrophotometric and voltammetric investigations of the reduced solutions. A further electrochemical characterisation of the formed reduction products 3-, 4- and 5-aminosalicylic acid was also carried out. It was found that the oxidation of the investigated azo compounds occurs according to two different pathways. Compounds with, at the most one hydroxyl group in the 2- or 4- position were shown to be irreversibly oxidised while Olsalazine sodium, its azoxy analogue and 2-hydroxy-5-[(3'-carboxy-2'-hydroxyphenyl)azo]benzoic acid disodium salt were oxidised in a reversible 2e-, 2H+ reaction. The oxidation product of Olsalazine sodium was characterised by UV/VIS and NMR spectroscopic methods and a structure for the oxidation product was proposed. The oxidative properties of Olsalazine sodium were also utilised to determine nM concentrations of this compound by liquid chromatography with electrochemical detection (LCEC).