Understanding the Photo- and Electro-Carboxylation of o-Methylbenzophenone with Carbon Dioxide

The lack of understanding of the radical reaction mechanism of Carbon dioxide (CO2) in photo- and electro-catalysis results in the development of such applications far behind the traditional synthesis methods. Using methylbenzophenone as the model, we clarify and compare the photo-enolization/Diels−Alder (PEDA) mechanism for photo-carboxylation and the two-step single-electron reduction pathway for electro-carboxylation with CO2 through careful control experiments. The regioselective carboxylation products, o-acylphenylacetic acid and α-hydroxycarboxylic acid are obtained, respectively, in photo- and electro-chemistry systems. On the basis of understanding the mechanism, a one-pot step-by-step dicarboxylation of o-methylbenzophenone is designed and conducted. Both the experimental results and related density functional theory (DFT) calculation verify the feasibility of the possible pathway in which electro-carboxylation is conducted right after photo-carboxylation in one vessel. This synthesis approach may provide a mild, eco-friendly strategy for the production of polycarboxylic acids in industry.