Jm. Tanko et Jf. Blackert, FREE-RADICAL SIDE-CHAIN BROMINATION OF ALKYLAROMATICS IN SUPERCRITICAL CARBON-DIOXIDE, Science, 263(5144), 1994, pp. 203-205
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.