An Iodine Catalyzed Protocol For The Synthesis Of Aryl Carboxylic Acids From Alkyl Aryl Ketones

As a useful intermediate,the carboxylic acids moiety is one of the most important functional groups in organic chemistry and can be easily converted into corresponding esters,acid halides,amides and anhydrides.Consequently,the development of efficient methods for the synthesis of aryl carboxylic acids has stimulated considerable interest.Part 1.A metal-free and one-pot two-step synthesis of aryl carboxylic acids from aryl alkyl ketones has been achieved.Acetophenone was selected as a model substrate to identify the optimal reaction conditions.Acetophenone can easily be converted into phenylglyoxal in high yields in the presence of iodine and DMSO.Then the green oxidant tert-butyl hydroperoxide?TBHP?is added to oxidize the intermediate to aryl carboxylic acids.The catalyst,solvent,temperature,the amount of I₂ and oxidant were sceened.On the basis of these experimental,we concluded that I₂?10 mol%?with DMSO?6 equiv.?in the first step,TBHP?2 equiv.?in the second-step and chlorobenzene as the solvent at 130 ^oC,after reacted for 3 h,86%isolated yield of benzoic acid could be obtained.The reaction tolerated various aryl alkyl ketones bearing electrondonating and withdrawing groups in ortho,meta and para positions of aromatic ring.This catalytic oxidation system displayed high reaction efficiency,and numerous aryl carboxylic acids and could be obtained in good to excellent yields?66%-94%?.Part 2.The I₂/DMSO+Fe?NO₃?₃.9H₂O/O₂ catalytic system was developed for synthesis of aryl carboxylic acids from aryl alkyl ketones.With acetophenone as the model substrate,the reaction conditions,including the amount of iron catalysts,the effect of solvent,and the reaction temperationwere screened.Under the optimized conditions?DMSO as the reaction solvent and oxidant,10 mol%Fe?NO₃?₃.9H₂O,10mol%I₂,O₂ as terminal oxidants,reaction for 12 h?,a variety of aryl alkyl ketones could be converted with good yields to products?51%-92%?.In summary,our group has developed two highly efficient and environmentally friendly catalytic oxidation systems for the oxidation of aryl alkyl ketones to produce aryl formate compounds.