Baeyer-Villiger oxidation of ketones in ionic liquids using molecular oxygen in the presence of benzaldehyde

A new and efficient method for the synthesis of lactones involving the application of an oxygen/benzaldehyde system as the oxidant and ionic liquids as solvents is reported. A significant rate enhancement was observed at 90 °C when the oxidation of ketones was carried out in the presence of a free radical initiator. The oxidation of model cyclic ketones, such as cyclopentanone, cyclohexanone, 2-methylcyclohexanone, 2-norbornone, 2-adamantanone and cycloheptanone gave lactones in high yields (84-90%) within relatively short periods of time, with the possibility of effective ionic liquids recycling. Additionally, discussion of the free radical mechanism of this reaction is proposed.