An Introduction to Multiphasic Chemistry

There are numerous types of multiphasic chemical processes. The most common are biphasic although triphasic, tetraphasic and even higher number of phases can also be used to conduct chemical synthesis. All the multiphasic methods aim to overcome the major problem of homogeneous catalysis, which is catalyst recovery and product separation. The simplest systems are biphasic ones that involve immobilizing a catalyst in one solvent, which is immiscible with a second solvent in which the substrates/products are dissolved. If a gas is required as a substrate then the system could be regarded as triphasic (i.e. liquid-liquid-gas), although for the purposes of this book (and as is most commonly defined elsewhere) such as system will be referred to as biphasic. In other words, only the number of different liquid solvent phases will be used to define the phasicity of a system. 

Chemistry in Alternative Reaction Media D. Adams, P. Dyson and S. Tavener 2004 John Wiley Sons, Ltd ISBNs 0-471-49848-3 (Cloth) 0-471-49849-1 (Paper) 

Should a third solvent be added which is immiscible with the other two, then a triphasic system results. The purpose of a third solvent may be, for example, as a built in cleaning step (see below). 

In general, there are four main types of biphasic processes, and they are generally used for catalysed reactions rather than stoichiometric ones. These four main processes are summarized below. 

---