Oxyhalogenation of aromatic molecules

In a typical halogenation reaction an aromatic substrate reacts with the elemental halogen in the presence of a catalyst or halogen carrier such as pyridine, iron(III) bromide or elemental iron itself. These reactions proceed well, but there are certain drawbacks bromine and chlorine are difficult to handle in the elemental form, and only half of the halogen 

2ArH + X2 + H2O2 2ArX + 2H2O ArH + HX + H2O2 ArX + 2H2O 

Benzene, toluene, ethylbenzene and chlorobenzene have been shown to be suitable substrates under these conditions, and the reaction rates were 50-70 times faster than for uncatalysed reactions. This reaction can be further enhanced by use of methanol as a cocatalyst [27], which allows bromina-tion of anilines in quantitative yield with complete selectivity for the para-isomer. 

A related system for the bromination of alkenes and alkynes using NaOCl, sodium bromide and a phase transfer agent such as tetra-butylammonium hydrogen sulfate has been reported [28]. In this reaction a third, red coloured phase formed between the aqueous and organic layers, which consisted mainly of tetrabutylammonium tribromide. This brominating system converted cyclohexene to 1,2-dibromocyclohexane (40%) and l-bromo-2-chlorocyclohexane (46%), 1-octyne to 1-bromo-l-octene (88%) and diphenylmethane to benzophenone (65%). 

---