Nitrate radicals generated by TiO2 heterogeneous photocatalysis: Application to the cleavage of C=C double bond to carbonyl compounds

The oxidative cleavage of alkenes represents a relevant chemical process with immense potential for the synthesis of partially oxidized compounds. Several methodologies have been proposed for achieving oxidative cleavage of alkenes, aiming to obtain carbonyl products. However, none of these approaches have been successfully scaled up for industrial applications beyond the laboratory scale. In this study, we report the selective photocatalytic oxidative cleavage of limonene to limononaldehyde using irradiated TiO2 suspensions in the presence of silver nitrate under ambient conditions. Results demonstrate that within one hour of irradiation, a notable conversion and selectivity of 60% towards limononaldehyde can be achieved. The investigation reveals that the oxidation process is primarily driven by nitrate radicals, generated through hole-induced oxidation of nitrate ions. Notably, this selective photocatalytic approach shows potentials that bode well for its application to other olefinic substrates in addition to limonene. These results present a promising pathway for the scalable industrial synthesis of partially oxidized compounds through selective photocatalytic oxidation of alkenes.