Polymeric reagents. IX Use of a polysterene-based amine oxide as a regenerable oxidizing agent for alkyl halides

Abstract

A new polymeric reagent based on a crosslinked polysterene matrix modified to incorporate tertiary amine oxide residues is useful in the oxidation of primary alkyl bromides, alkyl iodides or benzylic halides into aldehydes. In all cases the yields are excellent and no overoxidation to form carboxylic acid is observed. The polymeric reagent can also be used to oxidize secondary alkyl bromides and iodides to the corresponding ketones, but these reactions are accompanied by significant side reactions which produce undersired alkenes. Unlike the corresponding low-molecular-weight reagents such as trimethylamine N-oxide, the polymer can be easily freed from impurities which cause significant side-reactions and does not require the use of scrupulously anhydrous reaction conditions for oxidation to occur. As expected, the use of the polymeric reagent also results in a simpler processing of the reaction mixtures, with filtration and evaporation of solvent as the isolation steps. The polymeric by-product of the reaction can be recovered quantitatively and be regenerated after washing, by treatment with hydrogen peroxide. The regenerated reagent is as effective an oxidizing agent as the starting polymer, and no significant loss of activity is observed after five reaction cycles.