Selective Air Oxidation Of Sulfides Catalyzed By Br₃^-resin

Sulfoxide is one of the most important fine chemical intermediates,which has been widely used in pharmaceuticals,agriculture and other fields.Usually,the sulfoxides are obtained by the selective oxidation of sulfides.Among various catalytic systems,using oxygen or air as green oxidant has received increasing attention in recent years.Hence,the development of a highly effective catalytic system is of crucial significance.Here,for the first time,Br₃^-resins were used as catlysts and TBN or NO_x^-ion exchange resins as cocatalysts for the selective oxidation of sulfides with air as oxidant.Three efficient catalytic systems,Br₃^-ion exchange resin/TBN/air,chloromethylated bead resin-supported Br₃^-ionic liquid/TBN/air and Br₃^-ion exchange resin/NO_x^-ion exchange resin/air,were constructed for the selective oxidation of sulfides.Br₃^-ion exchange resin/TBN/air catalytic system:five kinds of Br₃^-ion exchange resin?IRA-900-Br₃,IRA-402-Br₃,717-Br₃,719-Br₃,D301-Br₃?were prepared based on commercial anion exchange resins and characterized by elemental analysis and Raman spectroscopy.The complete conversion of thioanisole and 96%yield of methyl phenyl sulfoxide with more than 99%selectivity can be obtained in the optimized conditions:1 mmol TBN,0.4 mL H₂O,and 20 m L acetonitrile as solvent at room temperature for 2 h.IRA-900anion exchange resin can be reused 4 times with no significant reduction in catalytic activity.IRA-900-Br₃ and IRA-402-Br₃ had better catalytic performances among 5 different types and sizes of Br₃^-anion exchange resins.And the applicability of the IRA-900-Br₃ catalyst was examined.It has excellent selective oxidation effect for 18 kinds of sulfides with different functional groups,and the yields were all above 90%.Chloromethylated bead resin-supported Br₃^-ionic liquid/TBN/air catalytic system:pyridine-type,alkylimidazole-type,tributylamine-type and tributylphosphine-type Br₃^-ionic liquids have been successfully immobilized on chloromethylated bead resin and characterized by FT-IR,Raman,elemental analysis,scanning electron microscope,and TGA.The optimal reaction conditions of pyridine-type ionic liquids catalyst were obtained:cat.0.1 g,TBN 1mmol,H₂O 0.5 mL.Comparative studies had shown that the pyridine and N-alkylimidazole type catalysts had better catalytic performance in different types of ionic liquid catalysts supported by chloromethylated bead resins.Catalytic oxidation test for 28 kinds of sulfide substrates using Br₃^-pyridine-type ionic liquids catalyst was carried out,the yield for the major were above 99%.Br₃^-ion exchange resin/NO_x^-ion exchange resin/air catalytic system:for the first time,six different catalytic systems were prepared using NO₃^-and NO₂^-anion exchange resins instead of homogeneous TBN.The conversion of thioanisole can be over 96%within 4 h.Finally,the applicability of the IRA-900-Br₃/IRA-900-NO₃ catalytic system was examined and oxidation of 10 sulfide substrates,and all sulfoxide yields were above 90%.