Influence of magnesium(II) ions on cathodic reactions in aprotic solvents—carboxylation of methyl aryl ketones

Abstract

The presence in the medium of free Mg^II leads to a complete change in the voltammetry for the reduction of 2-acetylnaphthalene in DMF–Bu₄NBF₄ saturated with carbon dioxide. The mechanism for these changes has been investigated and it is confirmed that the Mg^II interacts with the radical anions formed in the initial electron transfer reaction. The relevance of these conclusions to electrocarboxylations carried out in undivided cells with a sacrificial Mg anode is discussed. It is concluded that all the Mg^II formed at the anode is complexed strongly by the final carboxylated products from the cathode reaction and therefore the cathode reaction occurs in an environment where no free Mg^II ions are available. On the other hand, the complexation of the carboxylated products stabilises them to unwanted further reactions, thereby improving the selectivity of the electrosynthesis.