Selective Photo‐Oxygenation of Light Alkanes Using Iodine Oxides and Chloride

Partial oxidation of light alkanes to generate alkyl esters has been achieved under photochemical conditions using mixtures of iodine oxides and chloride salts in trifluoroacetic acid (HTFA). The reactions are catalytic in chloride and are successful using compact fluorescent light, but higher yields are obtained using a mercury lamp. In this photo‐initiated oxyesterification process, the robust alkyl ester products are resistant to over‐oxidation, and under optimized conditions yields for alkyl ester production of ∼50 % based on methane, ∼60 % based on ethane (with a total functionalized yield of EtX (X=TFA or Cl) of 80 %) and ∼30 % based on propane have been demonstrated. The reaction also proceeds in aqueous HTFA and dichloroacetic acid with lower yields. Mechanistic studies indicate that the process likely operates by a chlorine hydrogen atom ion pathway wherein alkyl radicals are generated, trapped by iodine, and converted to alkyl trifluoroacetates in situ. Partial oxidation: A new photo‐driven oxygenation of light alkanes using iodine oxides and catalytic chloride providing alkyl esters in high conversion and yield is reported. The new photo‐OxE process provides a substantial increase in the yield of alkyl ester products. Furthermore, mechanistic studies provide insight into the reaction pathway. Here, cyclohexane is used as a model substrate and it is found that the kinetic isotope effects for the thermal and photolytic processes differ significantly, indicating that the processes occur through distinct mechanisms.