Investigation of the anodic acetoxylation of p-methylanisole (p-MA) in glacial acetic acid medium using graphite (sp2) and BDD (sp3) electrodes

The electrochemical investigation of carbon fiber (CF) and boron-doped diamond (BDD) ultramicroelectrodes (UME) in glacial acetic acid medium has shown that the overpotential for acetate oxidation is higher on BDD than on CF. Preparative electrolyses have revealed that the main anodic products correspond to the Kolbe reaction. Beside these products small amounts of methane and methyl acetate are formed in different amounts depending on electrode material. This difference has been attributed to the different adsorption properties of CF (sp2) and BDD (sp3). Electrochemical measurements of p-MA in glacial acetic acid media have shown that p-MA is firstly oxidized to the corresponding radical cation. This intermediate, formed at both CF and BDD electrode, can either be attacked by the AcO− nucleophile leading to acetoxylated product or undergo dimerization ending up in polymeric material. The obtained results show clearly that on graphite acetoxylation is favored contrary to BDD where the dimerization step also takes place. Selectivity up to 93% monoacetoxylated product can be achieved on graphite for more than 90% conversion of p-MA using a bipolar capillary gap cell.