Free-radical side-chain brominations of alkylaromatics in supercritical 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-CO (2) is similar to that observed in conventional organic solvents. Also, SC-CO2 is an effective alternative to carbon tetrachloride for use in the classical Ziegler bromination with N-bromosuccinimide. Reaction yields are high, side products are minimized, and bromine-atom selectivities are observed. Thus, SC-CO (2) must be useful as a viable, environmentally benign substitute for many of the solvents typically used for free-radical reactions.