'Green' Halogenation Reactions: Oxidative Aerobic Halogenation and 'On Water' Bromination with Hydrobromic Acid and Hydrogen Peroxide

摘要

1.Introduction Halogenation of organic compounds is one of the most important transformations in organic synthesis. Molecular bromine, as the classical reagent for achieving this conversion, is both toxic and corrosive and its high reactivity resulting in highly exothermic reactions makes performing bromination in a selective manner difficult. Furthermore, by using molecular bromine only half of the bromine atoms are utilized while the other half ends up as HBr -a potentially hazardous pollutant. Alternative brominating agents, such as tetraikylammonium tribromides[1] and N-bromosuccinimide[2], have been used increasingly for bromination of organic compounds resulting in an easier handling and higher selectivity of reaction. Nevertheless, the use of these brominating agents has some limitations including low atom efficiency, need for removal of the reagent residue and finally, molecular bromine is needed for their preparation. On the other hand, nature has developed a molecular halogen-free strategy for halogenation using hydrogen peroxide (haloperoxidase) or oxygen (flavin dependent halogenase) and X-to produce "X+" in the enzymes active site[3].