Oxidation of 2-mercaptobenzoxazole in aqueous solution: solid phase formation at glassy carbon electrodes

The redox reactions of 2-mercaptobenzoxazole (MBO) have been investigated b y cyclic voltammetry at glassy carbon electrodes in aqueous solution. Four anodic and three cathodic processes could be identified. A more detailed an alysis of the oxidation processes up to a potential of +0.6 V (SCE) and the corresponding reduction signals showed that the oxidation leads to bis(ben zoxazolyl) disulfide (BBOD). Owing to its low solubility, the oxidation pro duct remains at the electrode surface. This product has been identified by ex situ FTIR and XPS analysis. During the reduction of BBOD, mainly MBO is formed. The remarkable lower solubility of BBOD in aqueous solutions compar ed to MBO allows preparation of layers of BBOD in situ and to control the a mount of deposited BBOD via the MBO solution concentration and electrolysis time. The peak potential and peak shape of the reduction signals change re markably as the amount of BBOD increases from submonolayer coverage to cove rages that correspond to multilayers. The behavior can be explained by assu ming an electrochemical conversion of BBOD microcrystals, which are deposit ed on the electrode surface, if the amount of BBOD formed during the MBO ox idation exceeds one monolayer.