Activation of C(SP3)–H Bonds Promoted Oxidation of Sulfides by O2 Under Catalyst-Free Conditions

Oxidation of organic sulfides is a significant reaction due to its application in many fields. Herein, we have developed a novel catalyst-free oxidation of organic sulfides by O2 under relatively mild conditions. The choice of the procedure was based on the well-acknowledged reactivity of the active C(sp3)-H bond of organic compounds to form the corresponding alkyl carbon free radicals (R·) in the presence of O2. The results showed that hydrocarbons such as tetrahydronaphthalene (THN) and cumene possessing the active C(sp3)-H bonds due to their lower bond dissociation energy (BDE), as a solvent, markedly promoted this catalyst-free sulfoxidation. It has been proved that reactive oxygen species (ROS) in this reaction are alkyl-peroxide radicals that are produced from R·, which is derived from the homolytic cleavage of the active C(sp3)-H bond with the help of heating and dioxygen, and further its activation of molecular oxygen. On this basis, combined with the DFT calculation of the activation energy of two reaction pathways, a possible reaction mechanism is proposed. The work provided a green synthesis approach of sulfoxide and sulfone compounds, and a scientific basis for a green process of ultra-deep desulfurization of fuel oils.

Zufeng Wang, Hongyi Wang, Zhiying Zhao, Yu Zhu, Youer Deng, Xiaolong Li, Dan Zeng, Yachun Liu, Chao Zhang and Zaihui Fu