Use of Biphasing in Organic Synthesis

The theoretical developments presented previously are quite general and are equally applicable to organic reactions without enzymes. However, in such cases, biphasing is only one of a number of strategies in which reaction is combined with a variety of separative techniques, for example, extraction, distillation, and crystallization. Therefore, it will be considered along with other strategies in Chapter 25 and will be concerned largely with methods based on the principles of acid-base reactions. 

In this section we describe a strategy generally called chemical protection by biphasing and another in which biphasing is used to dramatically enhance the scope of homogeneous catalysis through development and use of novel catalysts characterized by their water solubility. The potential of the latter appears to be enormous. 

By chemical protection we mean protecting a chemical species produced by a reaction from undergoing further conversion to an unwanted product by removing it from the scene of the reaction. For example, in the reaction 

There are essentially two methods of protecting a desired product by biphasing  

An example of category I is the preparation of optically active epibromohydrin by base-catalyzed hydrolysis and dehydrogenation of the monoester of phthalic acid, as shown in reaction 18.15. 

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