Organic Synthesis in Water/Carbon Dioxide Emulsions

Abstract

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.

Selective Oxidations on Recoverable Catalysts Assembled in Emulsions

“…The emulsion catalysis functions as highly dispersed nanoreactors and behaves like homogeneous catalysis. The biphasic catalytic systems are different from those reported by other groups [14][15][16], the amphiphilic catalyst can be assembled in the interface of emulsion, droplets in the reaction system, not in the continuous phase or inside the emulsion droplet. In addition, the emulsion droplets can be demulsified by centrifugation and easily separated and recycled.…”

“…One of the most general and efficient methods that can overcome this disadvantage is to use surfactants, which solubilize the reactants or form colloidal dispersion in reaction systems. The biphase systems thus obtained include phase-transfer catalysis [4][5][6][7][8], micellar catalysis [9][10], and microemulsion [11][12][13] or emulsion [14][15][16][17][18] according to the different reaction circumstances.…”

“…With the exception of the emulsion polymerization in chemical manufacturing [19], however, only a limited number of practical examples have been reported for catalytic reactions to date [11][12][13][14][15][16]. For the reactions in the emulsions, colloidal particles are formed with surfactant molecules that provide a high interfacial surface area and intensify the reaction.…”

“…However, one major shortcoming is that the emulsion droplet is usually difficult to demulsify after the reaction. Thus it is uneasy to separate the catalyst, surfactant and products from the reaction system [2,[13][14][15][16].…”

Spectroscopic Investigations of Intermolecular Interactions in Supercritical Fluids

“…Over the past few years several key aspects of the PFPE/scC0 2/H 2 0 system have been investigated, including their phase equilibria, water pool and micelle shape, and internal dynamics [38], the pH within an unbuffered PFPE water pool [39] and a means to control the water pool pH within PFPE micelles [40]. Several researchers have also shown that one can use the PFPE/C0 2 /H 2 0 system to perform inorganic [41] and organic [42,43] reactions directly within the micelle water pool. Researchers have also used these micelles to prepare tailored, uniform CdS nanoparticles [44].…”