Electmphilic aromatic bmminatbn of phenol ethers in superacki medium can be achieved with sodiim or potassium bromide. The yield and selectivity are lower than wtth bromine, the oxidation of the halide to the electmphilic halogen catbn is obtained by concomitant reduction of antimony per&fluoride. Setectivtty is observed only in methylanisole. The electrophilii aromatic bromtnatbn of aromatic derfvatfves has been achieved wfth bromine activated in a variety of solvent systems such as ltqrtd SO2.l HClO4,2 CF8S08H,8 CF8SO+g in CHQ4 and HF-SbF5.5-1 o Bromine has also been combined wfth bromide bn in ammonium trtbromtdss as mild and effiient brominating reagents.11 a,b
On the basis of our recent finding of the remarkable selecttvity in the superacid catatyzed C-H bond acttvatbn in the presence of bromide ions12, we have investigated the possibility of using alkali bromides as reagents for brominatiin of phenol ethers. We have chosen these substrates especially because they have already been studied in detail with the Br2+tF-SbF5 system.
We compare here the yield and selsctMt&s found tn both systems and disarss the nature of the electrophilii species.
Experimental procedure
Bromine or the akalt bromide and the phenol ether are added tn a KeCF reactor contalntng HF-SbF5 (4-20 mol % SbF5) at -78%. Qenerally the molar ratii was SbF5 : 10 I : 1.4 or eq.Br2 : 0.7 I substrate : 1. The temperature of ths magnetkxilly stirred sokrtbn is then raised to -40" for 15 minutes before neutraffsatton and ether extractbn. ldentifkatbn of the pmducts has been made on the basis of G.C. analysis (FFAP 8 m) and mass spectmmetry.