The fluorous phase: Organic chemistry with highly fluorinated reagents andsolvents

Perfluorinated hydrocarbons and related ethers and amines have emerged only recently as unique solvents with interesting applications in organic synth esis. Since they are immiscible with water and with many common organic sol vents, they represent a third liquid phase commonly called the fluorous pha se. Their high solubility for oxygen allows some efficient and selective ae robic oxidation reactions under mild conditions. Individual components of a reaction mixture (products and by-products, excess of substrates and reage nts), which bear perfluoralkyl substituents of sufficient size and number, can be selectively extracted into the fluorous phase. This is the basis of the so-called fluorous synthesis, a new separation and purification techniq ue taking advantage of organic/fluorous and fluorous/organic phase switches . A technique called fluorous biphase catalysis exploits not only this prin ciple but also the ability of certain perfluorocarbon/hydrocarbon (aromatic s) biphase mixtures to form a homogeneous solution at elevated temperature. A highly fluorinated catalyst can thus be applied under homogeneous condit ions and can be recovered from the fluorous phase after phase separation at lower temperatures.