What is Required from Alternative Solvent Strategies

What is Required from Alternative Solvent Strategies  

6 WHAT IS REQUIRED FROM ALTERNATIVE SOLVENT STRATEGIES  

Exceptions to this rule of high recovery may be made for CO2 and water, which are non-toxic and may be returned to the environment providing that 

If nonvolatile liquids are to be used to avoid the problems associated with volatile organic solvents, then it is very desirable that there is some convenient way of recovering the reaction products from the liquid. This approach is used in the biphasic systems described in Chapters 2-5. In the fluorons biphase (Chapter 3), reagents and catalysts are fine-tuned by adding perfluoroaUcyl chains, known as ponytails , to ensure that only those chemicals will mix with the fluorons layer. Pnriflcation is simply a matter of separating the two phases. Transition metal catalysts with fluorous ligands will remain in the fluorous phase, and the whole catalyst-solvent mixture may be reused for another batch of reactions, as shown schematically in Fignre 1.20b. 

Ionic liquids may be used in a similar fashion, bnt in contrast to the extremely nonpolar fluorous solvents, ionic liqnids are polar. They are completely nonvolatile and so cannot be lost to the atmosphere. A range of ionic compounds that are liquid at room temperature and their nse in synthetic chemistry are described in Chapter 4. 

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