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4711182 
Journal Article 
Environmentally benign electrophilic and radical bromination 'on water': H2O2-HBr system versus N-bromosuccinimide 
Podgorsek, A; Stavber, S; Zupan, M; Iskra, J 
2009 
1 
Tetrahedron
ISSN: 0040-4020 
PERGAMON-ELSEVIER SCIENCE LTD 
OXFORD 
65 
22 
4429-4439 
English 
WOS:000266296100023 
A H2O2-HBr system and N-bromosuccinimide in an aqueous medium were used as a 'green' approach to electrophilic and radical bromination. Several activated and less activated aromatic molecules, phenyl-substituted ketones and styrene were efficiently brominated 'on water' using both systems at ambient temperature and without an added metal or acid catalyst, whereas various non-activated toluenes were functionalized at the benzyl position in the presence of visible light as a radical activator. A comparison of reactivity and selectivity of both brominating systems reveals the H2O2-HBr system to be more reactive than NBS for benzyl bromination and for the bromination of ketones, while for electrophilic aromatic substitution of methoxy-substituted tetralone it was higher for NBS. Also, higher yields of brominated aromatics were observed when using H2O2-HBr 'on water'. Bromination of styrene reveals that not just the structure of the brominating reagent but the reaction conditions: amount of water, organic solvent, stirring rate and interface structure, play a key role in defining the outcome of bromination (dibromination vs bromohydroxylation). In addition, mild reaction conditions, a straightforward isolation procedure, inexpensive reagents and a lower environment impact make aqueous brominating methods a possible alternative to other reported brominating protocols. (C) 2009 Elsevier Ltd. All rights reserved.