Organic synthesis in water carbon dioxide emulsions

The synthetic reaction between a hydrophobe, benzyl chloride, and a hydrophilic nucleophile, KBr, is reported in water-in-carbon dioxide (w/c) and carbon dioxide-in-water (c/w) emulsions. Emulsions containing equal amounts of water and CO2 were formed with both anionic perfluoropolyether ammonium carboxylate (PFPE COO-NH4+) and nonionic poly( dimethylsiloxane)-g-poly(ethylene oxide) and poly(butylene oxide)-b-poly(ethylene oxide) surfactants, without the need for any added cosolvent. Higher yields of benzyl bromide were obtained in w/c and c/w emulsions (41-47%) as compared to water-in-octane emulsions (33%). Yields were much higher than in a previous study of the same reaction in a w/c microemulsion (Jacobson et al. J. Org. Chem., following paper in this issue), since the much larger amount of water in the emulsion allowed for a greater excess of KBr.