Ligand-induced Selective Oxidation Of Sulfides With Molecular Oxygen

Sulfoxides and sulfones are a class of widely used organic compounds,which not only functionalize as chiral ligands in the catalyzed asymmetric synthesis,but also exist in various chemical substances,such as pharmaceuticals,agrochemicals and functional materials and so on.Selective oxidation of sulfides is one of the most direct and common methods for the synthesis of sulfoxides and sulfones,and it is also applied in the removal of sulfur compounds in fossil fuel or industrial waste.Oxygen,as the highly abundant,cheap and clean oxidant,has always been a centered research.At present,there are many problems still existed in the study of selective oxidation of sulfides employed oxygen as an oxidant,such as harsh reaction conditions,poor conversion and selectivity,and poor universality.Moreover,there are few reports on the selective oxidation of sulfides to sulfones with oxygen as an oxidant.In this paper,we present a highly efficient and applicable process for the ligand-dependent selective synthesis of sulfoxides and sulfones through oxidation of sulfides with O₂ catalyzed by the cheap and readily available CuSO₄/TEMPO.Firstly,we developed a simple,green,highly efficient,recyclable and highly selective method of the selective oxidation of sulfides to sulfoxides.And the significant contribution to this work is the excellent product yielding up to 99%of sulfoxides,selectively oxidized from various aromatic and aliphatic sulfides.In addition,catalyst/product separation is quite straightfoward through the precipitation and filtration.It was demonstrated that the as-obtained solid could be reused without considerable loss of activity during the oxidation reaction which is CuSO₄/pyridine complex verified by single crystal diffraction.Based on the above work,we found that the substituents on pyridine have a great influence on the selectivity for the oxidation of sulfides.Using 4-methoxyisoquinoline or 3,5-dimethylpyridine as a ligand,sulfides can be oxidized to sulfones with high efficiency and selectivity.Similarly,the copper catalyst can be recycled.Finally,the reaction kinetics and possible catalytic mechanism was proposed.