FREE-RADICAL SIDE-CHAIN BROMINATION OF ALKYLAROMATICS IN SUPERCRITICAL CARBON-DIOXIDE

Free-radical side-chain brominations of alkylaromatics in supercritica l carbon dioxide (SC-CO2) are reported. Direct bromination of toluene and ethylbenzene form the corresponding benzyl bromides in high yield. The observed selectivity in SC-CO2 is similar to that observed in con ventional organic solvents. Also, SC-CO2 is an effective alternative t o carbon tetrachloride for use in the classical Ziegler bromination wi th N-bromosuccinimide. Reaction yields are high, side products are min imized, and bromine-atom selectivities are observed. Thus, SC-CO2 must be useful as a viable, environmentally benign substitute for many of the solvents typically used for free-radical reactions.