Phase-transfer catalyst

By using a PTC process, one can achieve faster reactions, obtain higher conversions or yields, make fewer byproducts, eliminate the need for expensive or dangerous solvents that will dissolve all the reactants in one phase, eliminate the need for expensive raw materials and/or minimize waste problems.

The catalyst for PBC has been designed in which the external part of the zeolite is hydrophobic, internally it is usually hydrophilic, notwithstanding to polar nature of some reactants.

[10] Subsequent work demonstrated that many such reactions can be performed rapidly at around room temperature using catalysts such as tetra-n-butylammonium bromide and methyltrioctylammonium chloride in benzene/water systems.

One of the more complex applications of PTC involves asymmetric alkylations, which are catalyzed by chiral quaternary ammonium salts derived from cinchona alkaloids.

[4][5][6][7][8] Stirring and mass transfer from the organic to the aqueous phase and vice versa are required for conventional catalytic system.

Conversely, in PBC, stirring is not required because the mass transfer is not the rate determining step in this catalytic system.

It is already demonstrated that this system works for alkene epoxidation without stirring or the addition of a co-solvent to drive liquid–liquid phase transfer.

[4][5][6] The active site located on the external surface of the zeolite particle were dominantly effective for the observed phase boundary catalytic system.

[7] [14] Modified zeolite on which the external surface was partly covered with alkylsilane, called phase-boundary catalyst was prepared in two steps.

Fully modified Ti-NaY (o-Ti-NaY), prepared without the addition of water in the above second step, is readily suspended in an organic solvent as expected.