Electrogenerated superoxide anion induced oxidative amidation of benzoin

Amide function is very important in both organic and medicinal chemistry. Benzamides can be obtained in good to high yields by reaction of benzoin, primary or secondary amines, molecular oxygen and electrogenerated superoxide anion (obtained with galvanostatic method). The advantage of using electrogenerated superoxide anion is related to its counterion, the tetraethylammonium cation, which is not tightly bound to the anion and thus renders superoxide highly reactive also in the absence of additives (necessary when using KO2). The reaction conditions are very mild and only 0.5 F/mol are necessary to obtain good yields in benzamides. This work points out that benzamides can be obtained also starting from deoxybenzoin and benzil, via CC bond cleavage, with yields which depend on the charge amount. A mechanistic hypothesis (in part supported by the literature and by voltammetric studies) is reported, which allows to explain the formation of byproducts and to define the role of oxygen and superoxide anion.