Perfluorocarbon compounds phase

On the heels of work by Zhu and Horvath and Rabai, perfluorocarbon solvents and fluorous reagents have been used increasingly in organic syntheses. Ruorous compounds often partition preferentially into a fluorous phase in organic/fluorous liquid-liquid extraction, thus providing easy separation of the compounds. Tris[(2-perfluorohexyl)ethyl]tin hydride combines the favorable radical reaction chemistry of trialkyltin hydrides with the favorable separation features of fluorous compounds. 

The system is presently limited to the treatment of vapor-phase waste streams. The process is not suitable for the disposal of solids, sludges, or liquids that cannot be readily vaporized. Tests have shown that the present design is not capable of destroying perfluorocarbon (PEC) compounds as efficiently as it destroys halogenated solvents. 

Curran and co-workers have introduced a promising approach to separation and purification procedures by using fluorocarbon-coated solid phases for liquid-phase chromatography. This approach depends on attaching a variety of perfluorocarbon tags to functional compounds which render the eventual substrate mixture separable over the perfluorinated stationary phase [27, 28] (Figure 7.8). 

Carbonyl compounds are more polar than olefins and therefore much less soluble in perfluorocarbons, so the aldehyde products were expelled from the fluorous phase and efficiently taken up in the organic phase. Most catalytic FBS reactions developed to date likewise have involved substrates of low polarity that are converted to more polar products. Some exceptions to this rule of thumb are known, however, as exempli lied by an efficient FBS process for the esterification of equimolar amounts of an alcohol and a carboxylic acid [7]. 

As an alternative to the use of fluorous tag, fluorous aqueous biphasic systems have also been explored. Recently, fluorous biphasic system composed of fluorous Lewis acid ytterbium perfluorooctanesulfonate [Yb(OPf)3], fluorous solvent perfluorocarbon has been used in the synthesis of benzodiazepines from OPD and carbonyl compounds [127]. Conceptually, the fluorous catalyst with perfluoroalkylated tails can dissolve into the fluorous phase containing the product after the reaction. The study has been extended later to the use of fluorous aqueous emulsion expecting that the organic substrate will remain in the interfacial area between a fluorous phase and aqueous media. Thus another synthesis of benzodiazepines has been reported by the same group by carrying out the reaction in a fluorous aqueous emulsion system composed of perfluorooctane and potassium perfluorooctanesulfonate at room temperature (Scheme 38) [128]. Moreover, the emulsion could be recovered and recycled without significant loss of activity. 

The high oxygen-carrying capacity of some perfluorocarbons makes them viable as artificial blood components (23), and yet to date the mechanism of oxygen binding to fluoro ethers is not well understood. Thus, it was of considerable interest to probe the ability of perfluoro macrocycles to bind molecular oxygen and other small molecules in the gas phase in order to obtain new information about the binding afflnities of these compounds (11). For these studies, each perfluoro macrocycle was admitted into the source of a triple... 

---