L-L-L-S Top layer = organic Middle layer = catalyst-

philic + catalyst Bottom layer = aqueous

Top layer = organic Bottom layer — catalyst-philic + catalyst

L-L-L-S Top layer = organic Middle layer = catalyst-

philic + catalyst Bottom layer = aqueous

liquid film. The perspective depends on the amount of this phase: if the catalytic amount of liquid quat (or ionic liquid) is used, it forms a membrane that adheres to the catalyst; while if an excess is present, it forms a third—catalyst-philic— liquid phase.

The nature of this ionic/hydrophilic liquid phase can be quite diverse: it can be made by an onium salt (e.g., ammonium or phosphonium), by an ionic liquid (e.g., imidazolium salts), by polyethyleneglycols, and even water. What is required is that the catalyst-philic phase is not miscible with the other phases (organic or aqueous phases).

Interest in multiphasic systems with a catalyst-philic phase derives from the following nine factors:

1. The ability to form three separate stable liquid phases is intriguing and peculiar.

2. The catalyst can be "immobilized."

3. The catalyst can be stabilized.

4. The catalytic activity can be modified.

5. Separation of products can be simplified.

6. Phase transfer (catalysis) becomes an issue.

7. The solvents used can be advantageous from an environmental standpoint.

8. There may be process advantages (intensification, separation, environmental, energy requirements, etc.).

9. Both homogeneous and heterogeneous catalysts can benefit from the new conditions.

Each multiphasic system is discussed separately, by first describing its composition and behavior, then by describing the reactions its has been used for, and finally by rating its efficiency, advantages, drawbacks, and so forth.

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